Treating Straw for Animal Feeding

7/30/2019 Treating Straw for Animal Feeding

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III. ASSESSMENT OF TECHNICAL FEASIBILITY

12. The objective of straw treatment is to increase the digestibility of straw and/or the amountof it voluntarily consumed so that digestible energy intake by animals from straw isincreased. Methods of treating straw may be classified broadly into physical, chemicaland biological categories. Among physical methods of significance are grinding andpressure cooking. Very fine grinding in ball mills and irradiation, while effective inimproving digestibility, are so expensive that they are unlikely ever to become

commercially significant. Chemical methods currently being developed all employ alkalis.Other chemicals like chlorine can also be used to improve digestibility but are moreexpensive and more difficult to handle than the alkalis and no technology involving theiruse has yet been developed. The alkali treatment methods may be classified as follows.

Wet methods

1. Beckmann (NaOH)

2. Modified Beckmann (Torgrimsby) (NaOH)

Dry methods

1. Industrial process (NaOH)

2. Farm scale treatment

a. Daily treatment (NaOH, Ca(OH)2, NH3)

b. Bulk treatment

i. followed by stacking (NaOH)

ii. followed by ensiling (NaOH, Ca(OH)2)

iii. of stacks under plastic sheet (NH3)

Wet methods involve soaking straw in 10 litres of chemical solution per kg of dry straw. Indry methods straw is sprayed with 0.1 to 3 1 of chemical solution per kg of dry straw orexposed to ammonia vapour. Wet methods employ a higher ratio of chemical to strawthan do the dry methods. In biological methods the aim is to increase digestibility of strawby culturing certain specific types of fungi on it. Each of these methods will be describedand its effectiveness assessed.

13. An essential preliminary, however, will be to describe the factors affecting the digestibilityof straw per se. Much new information, some unpublished, is now available on this
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subject. This information is indispensable to a correct assessment of straw treatment.

Factors affecting the digestibility of straw

14. The causes of variability in the digestibility of straw when fed to animals are:

1. intrinsic causes (specie, variety, environment, methods of harvesting and handling)

2. the way the straw is fed to animals (diet composition and level of feeding)

If the straw is treated then a third factor is the efficiency of treatment. This will bediscussed separately for each of the methods dealt with later in this section. The first andsecond are discussed in the following paragraphs.

Initial digestibility of straw

15. Some digestibility and energy values for straws are presented in table 1. Variability islarge both among species of straw and within species and there are few clear-cutconsistent differences. In Europe wheat and rye straws are considered by scientists andfarmers alike to be poorer than barley and oats straw. This is in a general way borne outby the data in table 1, but the variability within species (see D value, column 4) makes itpossible to get samples of wheat straw which are better than some samples of barleystraw in the same year from the same area. Much of this is due to varietal differences asevidenced by the data for the T.D.N. values of Canadian straws (column 7); the cropswere all grown in a single, replicated field experiment. Similar varietal variability has alsobeen reported from India by Kharat (1974) for wheat and by Saleem and Jackson (1975)for paddy. There was no difference between older, long-strawed varieties and newer,short, stiff-strawed varieties in these two studies. In Britain it is commonly believed thatspring barley straw is more digestible than winter barley straw and the Ministry ofAgriculture, Food and Fisheries tables (column 9) give metabolisable energy values of 7.3and 5.8/kg, respectively. Recent British data (column 4) does not, however, support thiscontention, nor does recent French data (column 2). Maize stover seems to be superiorto other straws.

16. Straws also vary in the amounts in which they are voluntarily consumed by animals.Mulholland et al. (1974) fed oat, wheat and barley straws ad libitum to sheep andrecorded dry matter intakes of 600, 400 and 300 g/day, respectively. Intake was positivelycorrelated with organic matter digestibility in vitro. Urea supplementation increased theintakes of all three straws, but the relative differences among them remained.

17. The digestibility of straw is affected by how it is harvested and subsequently handled.Leaves are more digestible than stems in all straws (except paddy, in which the reverseis true; Saleem and Jackson, 1975) and thus the height of cutting the crop at harvestinfluences digestibility. Xande (1977) found that straw picked up from the fieldimmediately after combining had a higher digestibility by about 2 units than straw that wasleft in the field for some time. This is presumably due to leaf loss and possibly to leachinglosses where rain falls on the combined straw before it is picked up.

Table 1. The digestibility/energy values of straws

Straw Organic-matter

digestibility

D

value

Enzyme

digestibility T.D.N. M.E. S.E.


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(1) (2) (3) (4) (5a) (5b) (6) (7) (8) (9) (10)

Barley,spring

45 4445(4049)

7.3 23

winter 43 5046

(4449)21 47

39

(3741)5.8

Wheat 36 42 4938

(3643)14 19 43

37

(3440)

46

(4254)5.7 13

Oat 45 49 5541(3648)

23 5042(3944)

6.8 21

Rye 44 16 45 6.3

Rice 22 4542

(3551)

Maize 57 7.3

Millet 20 4752

(4856)

Sorghum 19

(1) Norw ay. %. Homb, 1947.

(2) France. %. Xande, 1977.

(3) Denmark. Organic-matter digestibility in vitro, %. Rexen, Isrealsen, Busk andWaagepetersen, 1975.

(4) U.K. Digestible organic matter in dry matter. A lderman, 1976.

(5a) Denmark. Danish straw s. % of dry matter digested. Rexen et al., 1976.

(5b) Denmark. Indian straw s. % of dry matter digested. Rexen et al., 1976.

(6) U.S.A. kg/100 kg dry matter. Morrison, 1959.

(7) Canada. kg/100 kg dry matter. Kernan et al., 1977.

(8) India. kg/100 kg dry matter. Sen and Ray, 1971.

(9) U.K. Metabolisable energy. MJ/kg dry matter. MAFF, 1975.

(10) U.K. Starch equivalent. Watson, 1941.

18. Busk and Kristensen (1977) sampled a large number of bales from one field anddetermined the enzyme digestibility of each sample. The average was 28 with a range of 19to 32.

19. The significance of the differences in initial digestibility is that they remain after alkalitreatment. This has been most clearly shown by the experiment of Rexen, Isrealsen, Buskand Waagepetersen (1975). Nine lots (each of 500 kg) of each of 4 types of straw-winterbarley, wheat, oats and rye-with initial average values for organic matter digestibility in vitro of

50, 49, 55 and 44, respectively (see column 3 of table 1) were chemically treated withdifferent amounts of NaOH (08 kg/100 kg straw) and pelleted. All the straws were improvedby increasing amounts of alkali at about the same rate and initial differences remained at alllevels of treatment. Similar results have been reported by Piatkowski et al. (1974a). It istherefore likely that differences in the digestibility of treated straw of as much as 10 unitscould be caused by differences in initial digestibility alone. Differences of this magnitudemight occasionally even occur among samples of treated straw of the same specie.

20. Wherever government extension services provide a feed testing service to farmers, thetesting of treated straw by an in vitro or enzyme solubility technique could be instituted. Suchtest values would indicate initial digestibility plus treatment effect and could be used toformulate specific feeding recommendations for individual farmers. In this connection the

enzyme solubility method developed in Denmark (B.Rexen, 1977) would appear to be useful.
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Diet composition

21. It is widely recognised that the supplementation of roughage with starchy feeds reducesthe digestibility of the roughage. The rate as well as the extent of digestion is affected.The results of an experiment done by Chimwano et al. (1976) with dried grass and

concentrates demonstrate this (table 2). The voluntary intake of a roughage is alsoreduced. Lonsdale et al. (1971) added barley to a dried-grass diet to the extent of 50%and found that for every 1 kg of barley consumed dried-grass consumption decreased by1 kg. Thus dry-matter intake did not increase by adding barley to the diet. They also foundthat the retention time of cellulose was increased as well as the dry-matter content of theentire alimentary tract. These changes seem to account for the lower intake of the driedgrass observed. Straw digestibility and intake have likewise been shown to be reduced byconcentrate supplementation (table 3 and 4). A further conclusion which can be drawnfrom the data shown in table 3 is that a roughage supplement, even a high-quality one likedried grass, does not depress straw digestibility as a concentrate supplement does.

22. In two recent experiments (Piatkowski et al., 1973; Rexen et al., 1975b) the digestibility oftreated straw was not found to be depressed by high levels (50%) of concentrates in thediet. Straw was treated with 45 kg NaOH/100 kg. These results are not incompatiblewith the conclusion arrived at in the preceeding paragraph. In the experiments of thesetwo groups of workers, treated straw was fed at restricted levels. It is widely recognisedthat the level of feeding a roughage affects its digestibility (review by Blaxter, 1961).Increasing level of intake depresses digestibility and the depression is greater with lessdigestible roughages like straw than with more digestible ones. The results of a recentexperiment done by Dulphy et al. (1977) (table 5) show how important level of feeding iswith treated straw. At a restricted level of feeding digestibility was not only higher but alsodid not decrease when increasing levels of concentrates were included in the diet. Thisfinding clearly shows why Piatkowski et al. (1973) and Rexen, Stigsen and Kristensen(1975) did not find any decrease in the digestibility of straw when they increased

concentrate levels.Table 2. Effect of proportion of barley-based concentrate and dried grass in the diet on the

disappearance of dried grass and cotton threads from dacron bags incubated in the rumen ofsheep

Proportion of concentrate in the

diet,%

Dried grass: loss in

weight,

(g/100 g) after:

Cotton thread: loss in

weight,

g/100 g after

6 h 12 h 18 h 24 h 24 h

100 27 40 43 46 075 35 42 48 55 3

50 37 43 57 66 13

25 40 54 68 75 26

0 46 64 74 78 33

SE of treatment means 3 3 3 3 5

Source: Chimw ano et al., 1976.

Table 3. The effect of the type of supplement on the organic-matter digestibility and intake ofwheat straw by sheep


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Type of

Supplement

Amount of

supplement, %of diet

Organic-matter

digestibility of straw, %

Dry-matter intake,

g

Straw Supplement

Concentrate 20 41 1143 287

(soyabea n meal andmaize)

Concentrate 45 30 829 638

(soyabean meal andmaize)

Dried grass 45 41 715 559

(high-quality)

Source: Dulphy, private communication-1977.

23. Blaxter et al. (1961) showed that the depression in the intake of roughage varied with thequality of the roughage; with a high-quality dried grass, 1 kg of concentrates reducedintake by 1 kg, but with a lower quality (i.e., lower digestibility) dried grass 1 kgconcentrate caused a reduction in intake by only 0.49 kg. Presumably the digestibility ofthe high-quality dried grass was depressed more than that of the low-quality one. Apractical implication of this finding is that the difference in digestibility and overall feedingvalue between a high-and a low-quality grass hay or s ilage is less in a production dietcontaining a high level of concentrates than is indicated by the results of digestibility trials.The data from a recent experiment with straw shows that this does, in fact happen; withconcentrate supplementation the digestibility of treated straw is depressed more than thatof untreated straw (table 4). Due to this differential rate of depression in digestibility, theapparent difference between treated and untreated straw in digestibility is reduced as thelevel of concentrate supplementation is increased; it can be decreased to zero with4050% concentrates. This is a likely explanation for at least some of the observationsmade from time to time that the alkali treatment of straw did not apparently improve itsdigestibility, or improved it only a little (see review by Jackson 1977). Similarly, in someexperiments where liveweight gains have not improved by the treatment of the straw inthe diet, the differential effect of concentratesin depressing straw digestibility may beresponsible. A further systematic study of this phenomenon should be given the highestpriority in research programmes on s traw utilisation; it should be given a high priority evenin programmes of research on conventional roughages like hay and silage.

24. The amount of nitrogen in the diet also affects the degree of improvement in digestibilitythat occurs as a result of alkali treatment. Donefer et al. (1968) measured the effect ofurea supplementation (2.5%) on the response of alkali treatment (8 kg/100 kg neutralisedwith acetic acid) of ground oat straw fed to sheep. Energy digestibility increased by 13.5units when no urea was given and 18.3 units when it was. Voluntary intake of straw was

depressed by 19 g/kg W0.75 on alkali treatment when urea was not fed, but increased by31 g when urea was added. rskov (private communication--1977) measured the effectof increasing levels of urea on the digestibility of treated and untreated straw. Themaximum digestibility for treated straw was obtained when 1.21.8% urea was added;the digestibility of untreated straw, on the other hand, did not increase with the addition ofurea. Kategile (1977) fed a diet of ground, NaOH-treated, maize cobs (90%) and

molasses (10%) to heifers and varied the amount of urea added from 0 to 1.25%.Digestibility of dry-matter increased linearly from 3960%.


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Table 4. The effect of level of concentrate supplementation on the organic-matter digestibility of

untreated and treated * wheat straw with diets given ad libitum to sheep

Level of supplementaryconcentrate, % of diet Organic-matter digestibilityof straw, %

Dry-matter intake, g/day (60

kg sheep)Straw Concentrates

Untreated straw

15 46 700 138

30 49 690 290

45 41 570 472

Treated straw

15 57 1102 216

30 52 1062 485

45 43 921 802

*4 kg NaOH/100 kg straw

Source: Breton, private communication fromDulphy--1977.

Table 5. The effect of level of intake and concentrate supplementation on the organic matter

digestibility of treated * wheat straw-based diets

Level of supplementary

concentrate, % of diet

Organic-matter digestibility of

straw, %

Dry-matter intake,

g/day

Straw Concentrates

Intake ad libitum

7.5 49 983 80

15 50 1322 233

30 43 1270 545

Intake restricted

7.5 57 875 71

15 59 851 142

30 58 680 281

* 4 kg NaOH/100 kg straw

Source: Dulphy et al., 1977.

25. To assess the effectiveness of any straw treatment technique, the difference betweenthe digestibility of the untreated and treated straw must be determined. From theforegoing discussion it is clear that if this difference is measured by digestibility trials withanimals it will be influenced by the following factors.

a. The effectiveness of the treatment

b. Any difference in the level of feeding between the untreated and treated straws. If theanimals are fed ad libitum, the voluntary intake of the treated straw will usually behigher than that of the untreated straw. This may decrease the difference indigestibility obtained.

c. The type and amount of other feeds/supplements in the diet. Too much


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easily-fermentable carbohydrate or too little protein/nitrogen will decrease thedifference in digestibility obtained.

It is apparent that if the objective is to assess the effectiveness of a treatment techniqueper se,the best way to determine the difference in digestibility is by an in vitro method.

Such values are not influenced by the animal at all, and are reasonably reproducible(Sundstol et al., 1977). Considerable reliance is therefore placed on in vitro values in thisreport. At the same time, treatment techniques must be assessed for their effectivenessin improving the feeding value of straw in the types of diets in which the straw is to beused in practice. The only completely adequate way to do this is by conducting feedingtrials in which the performance of animals is measured. Changes in digestibility andintake can be determined at the same time. If full-scale feeding trials are not feasible forpreliminary investigations, simpler digestibility and intake trials may be done, but the dietsshould be those that would be used in a feeding trial. Where an untreated straw diet is thelocal practice, such a diet should be compared with a similar diet in which the straw hasbeen treated. If the objective is to determine whether treated straw can replace anotherfeed in the local diet, then three diets must be included in the trial. The first is the local

diet. In the second and third diets untreated and treated straw, respectively, aresubstituted for one of the components of the local diet. Examples of this type of trial arethose conducted by Pirie and Greenhalgh (1977) (on beef steers) (paragraph 62) and byBergner et al. (1976) (on milking cows) (paragraph 56). Many trials conducted to datehave either been digestibility trials comparing untreated and treated straws in a diet that isirrelevant to the prevailing local feeding practices, or feeding trials in which treated straw,but not untreated straw, has been substituted for another feed in a local diet. In thesecond type of trial it is assumed that the treated straw is better than untreated straw,but, in view of the evidence presented earlier in this section, this assumption may notalways be valid.

Physical treatment

26. The subject of grinding of roughages was critically reviewed by Greenhalgh andWainman in 1972. With all-roughage diets, grinding causes an increase in intake andweight gain. These effects are greater for roughages with lower digestibility; however,nitrogen can be a limiting factor to improvement by grinding for very poor roughages likestraw. Grinding usually decreases digestibility, but at the same time increases the netenergy value of the straw somewhat because the nutrients that are digested are utilisedmore efficiently by the animal. This improvement in net energy value may be moremarked with poor quality roughages.

27. The grinding of straw appears to give much less improvement in feeding value than alkali

treatment, at least in terms of digestible organic-matter intake. This is evident from thedata in table 6. In general terms also, grinding does not increase digestible organic matterintake by more than about 30% (review by Greenhalgh and Wainman, 1972), whereasalkali treatment increases it by up to 100%(e.g., table 19).. The improvement in thenetenergy value of straw by grinding might narrow the difference in terms of net-energyintake, but is unlikely to alter the conclusion that alkali treatment is about twice aseffective as grinding in increasing the feeding value of straw. The effect of grinding is alsomuch less or even nil when straw comprises 50% or less of the diet. What remains to beconsidered is the effect of grinding in conjunction with alkali treatment. The results of anexperiment conducted by Fernandez Carmona and Greenhalgh (1972) indicate anadditive effect of grinding and alkali treatment (table 6). The digestible-energy intake bysheep on a ground and alkali-treated straw diet was 15% greater than on a diet ofchopped alkali-treated straw. Feeding trial data are needed to determine if grinding inaddition to alkali-treatement is economically worthwhile. The grinding of straws before


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alkali treatment in some straw-processing plants is done to facilitate the subsequentmixing of the treated straw in commercial concentrate mixtures (paragraph 51).

Table 6. The effect of milling and alkali treatment of barley straw on digestibility and intake by

sheep *

Untreated straw Treated straw+

Chopped straw**

Organic-matter digestibility, % 45 61

Dry-matter intake, g/kg W0.75 27 48

Digestible energy intake, Kcal/kg W0.75 46 114

Milled straw***

Organic-matter digestibility, % 45 64

Dry-matter intake, g/kg W0.75 36 54

Digestible energy intake, Kcal/kg W0.75 60 132

* The straw w as supplemented w ith purified soyaprotein at the rate of 8 g/100 g straw . Thedigestibility of this supplement

w as assumed tobe 100%--data are for straw only.

** Straw chopped into 23 mm lengths

*** Straw milled in a hammer mill through a 2 mm sieve

+ Straw spray-treated w ith 8 kg NaOH/100 kg andneutralised w ith 7.4 kg propionic acid

Source : Fernandez Carmona and Greenhalgh, 1972.

28. The pressure cooking of sugarcane bagasse and wood chips has been found to increasedigestibility. Donefer and pathirana (1976) treated samples of bagasse with 4% NaOH

and with high pressure steam (8 kg/cm2 at 170) and found increases in cellulose

digestibility in vitro of 15 and 17 percentage units, respectively (initial digestibility 25%).Higher pressures and temperatures than these give still greater increases in digestibility.A company in Canada has developed equipment for pressure-cooking wood chips.Increases in digestibility in vitro are reported to be from 1520% to 5060% for aspen treechips (Stake Technology Ltd., Canada, private communication--1978). Treated materialhas a dry-matter content of 55% and a pH of 3.53.8. The low pH is due to the release oforganic acids during treatment. Guggolz et al. (1971) pressure cooked grass straws at a

pressure of 30 kg/cm2 and found an increase in digestibility in vitro of 20 percentageunits. When they added 3 g NaOH/100 g straw before pressure cooking the increase was40 units. When the same group (Garrett et al., 1974) treated rice straw in this way andfed it to sheep, digestibility and intake were reduced when NaOH was not added, but

were increased when it was. Even then pressure cooking with NaOH was no better thanNaOH treatment and heating for 15 min to 100. Possibly the temperature was too high,causing charing of the pressure-cooked straw. When they treated bagasse in this waythey found a large increase in phenolic-like compounds (Campbell, 1973). Somewhatlower temperatures might give useful results. If this method (without NaOH) is aseffective on straws as the best NaOH treatment methods, it merits further study. Oneadvantage it has over alkali treatment is that it contains no residual solium. Thedisadvantages are its high moisture content and the fact that capital investment might betoo high for small farms.

Chemical treatment--wet methods

29. Interest in the chemical treatment of straw revived in the 1960s with the introduction of


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the dry treatment method in which straw is simply sprayed with a limited volume of analkali solution. This development overcame the obvious disadvantages of the olderBeckmann method of high water requirement and high dry-matter losses, and made theindustrialisation of straw treatment possible. The fact remains, however, that the qualityof Beckmann-treated straw is higher than that of spray-treated straw. It is therefore a

welcome development that modified Beckmann methods have been devised whichreduce or eliminate dry-matter loss and hence environmental pollution. Waterrequirement is also drastically reduced. To obtain a proper perspective on these modifiedBeckmann processes, the original method will first be described and commented upon.

Beckmann method

30. A very interesting review of the early research on the alkali treatment of straw and thedevelopment of the Beckmann method has been presented by Homb et al. (1977). Theearlier reviews by Homb (1947 and 1956) are also recommended. There has been atendency to overlook the results of this valuable earlier work. The chemistry of strawtreatment was reviewed recently by Jackson (1977).

31. The scale of operation and the degree of mechanisation of the Beckmann treatmentprocess vary widely, but in all installations two tanks are employed. The straw isimmersed in a 1.5% solution of NaOH for 1820 hours. The volume of solution is 810 l.per kg of dry straw, which is enough to cover the straw, and provides 1215 kgNaOH/100 kg straw. After 1820 hours, the treatment solution is pumped to the othertank and fresh water is pumped in. The wash water overflows into a drain when the tankis full. This washing continues for 1820 hours after which the tank is drained. The strawis then ready to be fed. Straw is treated in a loose or baled form and chaffing isunnecessary for treatment or for subsequent feeding; on the other hand long baled strawis easier to handle during treatment than chaffed straw. The used NaOH treatmentsolution, after being transferred to the second tank, is made up to volume (by addingabout 300 1 water/100 kg straw) and NaOH strength (by adding approximately 8 kg

NaOH/100 kg straw). In most plants the volume of the treatment solution is made up withthe first wash water from the first tank to economise on alkali. In this way netconsumption of alkali is about 6 kg/100 kg straw. The next day, the treatment solution ispumped back to the first tank again and thus one batch of treated and washed straw isproduced every day. In the Norwegian installations, both cooperative and farm-scale, thestraw is lifted into and out of the tanks with travelling, electric chain hosts. Some furtherdetails of the operation of the Norwegian co-operative straw-treatment plants are given inparagraph 131.

32. The Beckmann treatment may also be done manually on small farms, as wasrecommended before the mechanised versions came into use in the 1950's (eg.,Watson, 1941). The treatment solution remains in the same tank and the straw is

transferred to the second tank which is used for washing only.33. Treated straw contains about 20% dry matter and is limp. The nodes should be soft; in

fact the softness of the nodes is a simple hand test applied to straw to determine theeffectiveness of treatment. Well-washed straw should not feel slippery or soapy. Thesodium content is 0.50.6% on a dry-matter basis (0.07-0.16% in original straw); the legallimit is 0.3%. Dry-matter losses are 2025 kg per 100 kg original dry-matter. Thedigestibility and feeding value of Beckmann-treated straw are discussed later inparagraphs 3740.

34. The effectiveness of the treatment depends upon time, temperature, pressure andamount of alkali. The effect of amount of alkali used on the digestibility of treated straw isshown by the results of an experiment done by Fingerling et al. (1923) (table 7). Twelvekg NaOH/100 kg straw may be near the amount needed to achieve maximum increase indigestibility. In the spray-treatment process maximum increase in digestibility in vitro isachieved with about 10 kg NaOH/100 kg straw. Fernandez Carmona and Greenhalgh


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(1972) found that the digestibility in vitro of treated straw increased linearly upto a level of14 kg/100 kg straw (2% solution) and levelled off thereafter. Piatkowski et al. (1977) havefound a large additional increase in digestibility when the amount of alkali was increasedfrom 10 to 20 kg/100 kg straw by increasing concentra tion from 0.5 to 1.0 (20 volumes ofsolution used;soaking for 24 hours). In many of the cooperative plants in Norway 20 kg or

more of NaOH/100 kg straw is routinely used (1518 volumes of a 1.5% solution), themanagers feeling that these quantities of NaOH are needed to give the soft texture theyaim at in treated straw. The exact amount of alkali needed in any situation wil dependupon the length of time the straw is soaked, the environmental temperature and thenature of the starting material. The influence of time and temperature are discussed inthe following paragraphs. No experimental data is available on the relative alkali needs ofdifferent types of straws for maximum increases in digestibility, but cooperative treatmentplant managers in Norway use a greater amount of alkali to treat wheat straw than to treatother types to get comparable texture in the finished products. Fortunately, the use of asizeable excess of alkali is feasible since all but about 6 kg NaOH/100 kg straw isrecovered in each treatment cycle whatever the amount present in the treatment solution.

Table 7. The effect of amount of NaOH used on the digestibility of

Beckmann-treated straw

Organic matter digestibility, %

Untreated straw 46

Treated straw, 2 kg NaOH/100 kg 46

Treated straw, 4 kg NaOH/100 kg 50

6 kg 61

8 kg 66

10 kg 66

12 kg 71

Source: Fingerling et al., 1923.

35. The effect of time on treatment effectiveness is revealed by the results of an experimentdone by Fingerling and Schmidt in 1919 (table 8). As a result of this experiment a soakingperiod of about 20 h became the recommended practice. Ferguson (1943) later foundthat this period could be reduced to 7 h in the summer in England without reducing theeffectiveness of treatment, but not in the winter. He also found that 4 h soaking and 19 hdraining were not as good as 23 h of soaking (the starch equivalent values calculatedfrom digestibility trial data were 47.6 and 51.2, respectively).

Table 8. The effect of duration of soaking on the digestibility ofBeckmann-treated straw

Organic matter digestibility, %

Untreated straw 46

Treated straw, 1.5 h 59

3 h 68

6 h 70

12 h 71

3 days 73

Source: Fingerling and Schmidt, 1919.

36. An effect of environmental temperature was also found by Ferguson (1943) (table 9). The

results of the extensive study done by Ololade et al. (1970) (table 10, right-hand column)indicate that still further increases in digestibility can be obtained if the treatment solution


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is heated upto the boiling point. Boiling was a feature of various pre-Beckmann methods,a feature that was dropped because it added unduly to the treatment cost.Table 9. The effect of environmental temperature on the digestibility of

Beckmann-treated straw

Temperature, degrees Digestibility coefficient,%

Crude fibre N.F.E.

0 69 50

7 73 49

3040 74 56

Source: Ferguson, 1943.

37. The advantage of the Beckmann method is that it gives a finished product of highdigestibility. Some organic-matter digestibility values have been presented in table 11.Increases on treatment range from 1427 percentage units. The range for straw treatedby dry methods is much lower (see paragraph 67). The main reason for the effectivenessof the Beckmann method is the high ratio of alkali to straw it employs, a ratio of 12 ormore kg NaOH to 100 kg straw, and the fact that the excess is washed out. When strawis treated by the dry methods not more than about 5 kg NaOH per 100 kg straw can beused, at least when straw constitutes a major part of the diet (70% or more). This isbecause excess alkali is not washed out. Somewhat more alkali can be used if the strawconstitutes 50% or less of the diet, but even then the increase in digestibility of dry treatedstraw does not go beyond the range 1520 units. The disadvantages of the Beckmannmethod are, of course, the high water requirement, dry-matter loss and river pollution.The treated straw is heavy (80% water) and must be prepared every day.

Table 10. Effect of temperature, duration of treatment and concentration of

sodium hydroxide on dry-matter digestibility in vitro (%) of barley straw*

(Source: Ololade et al., 1970).

Temperature Processing durationSodium hydroxide (% of dry matter)

0 2 4 6 8 12

(hours)

23 0 38 39 42 41 42 39

24 38 44 54 63 68 68

(minutes)

60 5 38 43 52 60 64 67

15 36 45 54 62 67 68

45 38 45 55 65 68 68

90 38 45 56 65 68 68

80 5 36 45 56 66 73 73

15 37 46 60 69 72 70

45 37 49 63 70 73 76

90 38 51 64 72 76 76

100 5 38 47 59 70 74 77

15 37 46 60 70 74 75

45 38 49 63 72 77 79

90 38 51 65 73 78 80

130 5 37 48 63 74 78 8015 38 49 65 75 78 81


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45 40 51 66 74 79 82

90 41 52 67 75 78 81* Each value is a mean of 3 replicates; for processing at 23 thepooled SE is 0.57 and HSD 3.24 at the 5% level of

probability,w hile f or processing at elevated temperatures these values are0.63 and 3.31, respectively.

38. Considerable variability is evident in table 11 in the degree of improvement in digestibility

obtained with the Beckmann method. This variability is even found among different trialsreported by an individual author. In Norway an increase in digestibility of 18 units wasobtained on an average in 4 trials (42 to 60--see table 11).

Table 11. The digestibility of untreated and Beckmanntreated straw

CountryType of

straw

Organic matter

digestibility, % Reference

Untreated Treated

Norway 42 60 Homb(1956)

Germany 46 71 Fingerling and Schmidt (1919)

46 73 Fingerling et al (1923)U.K. Oat 53 68 Watson (1941)

Wheat 47 65 -"-

Barley 46 60 -"-

Barley 45 71Fernandez Carmona andGreenhalgh (1972)

Later farm trials gave average treated straw digestibilities of 66 (for unchopped straw in 5trials) and 68 (for chopped straw in 10 trials). The average value for treated straws from all19 trials was 66, but the range was from 5676 (Homb, 1947). Some further data on thevariability in the digestibility of treated straws has been given by Ferguson (1943) (table 12).

Table 12. The digestibility of Beckmann-treated straw

Type of

straw

Number of digestibility

trials

Organic matter digestibility,

%

Average Range

Oat 11 68 6178

Barley 4 65 6069

Wheat 22 67 6470

Source: Ferguson, 1943.

39. Two production experiments in which treated and untreated straw were fed are known to

have been conducted. One was done on Indian village heifers by Kehar and is describedin paragraph 88. The other was done by Saxena et al. (1971). They fed growing lambsdiets containing 78% straw and 22% of a concentrate supplement. The results are shownin Table 13.

Table 13. The effect of treatment of straw (by the Beckmann method) on theperformance of growing lambs

Diet

Untreated

strawTreated straw

Untreated

straw

Treated

straw

+ + + +Soyabean Soyabean urea urea


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meal meal

Feed intake, g

DM870 1290 820 1110

Daily gain, g 62 177 53 125

g feed/g gain 14.6 7.3 15.3 8.8

Source: Saxena et al., 1971.

40. Beckmann-treated straw has been prepared and fed to livestock on farms in Norway forthe past 40 years. The usual amount of treated straw fed to milking cows is 1520 kg perday or 1/3 to 1/2 of the roughage offered. Heifers, bulls and s teers are fed 816 andoccasionally even 24 kg straw per day. In feeding trials with milking cows, treated strawwas found to be equivalent to good quality grass silage in calculated net-energy value(Homb et al., 1977).

41. Several experiments have been done to compare the use of Ca(OH)2 and NaOH for the

treatment of straw by the Beckmann method (Abou-Raya et al., 1964; Abou-El-Hassan etal., 1971). Though Ca(OH)2 is a strong alkali like NaOH, it has been found to be less

effective in increasing digestibility (table 14). This is probably because it is only sparinglysoluble in water. Its use has also been investigated with dry treatments and the findingswill be referred to later (paragraphs 63 and 75).

Modified Beckmann method-Torgrimsby method

42. The most immediate problem with the Beckmann method was that of river pollution. Ifwash water could not be discharged, it would have to be recycled. Torgrimsby (1971)suggested a closed system in which the amount of water added to the system is equal tothe amount removed in the treated straw. The method was further developed by Wethje(1975) and is being successfully used on his farm in Sweden. Preliminary experimentshave been conducted at the Agricultural University of Norway in which the system hasbeen run for 6 months continuously, producing a batch of treated straw every day.Evaluation of the straw is being done. This method is described in detail in paragraphs4448 below.

Table 14. The digestibility of NaOH and Ca(OH)2 of Beckmann-treated straw,

%

Alkali usedMaize stover Sorghum stover

Crude fibre N.F.E. Crude fibre N.F.E.

Untreated 52 59 50 51

Ca(OH)2 77 65 84 59

NaOH 92 61 94 69Source: Abou-Raya et al., 1964.

43. At the same time, several experiments have been done at various places with theBeckmann method modified only in that less wash water was used. Piatkowski et al.(1977), for example, treated straw with 20 l of a 1.5% NaOH solution per kg straw for 24hours in the usual way. The straw was then washed with only 4 l water/kg straw. Organicmatter digestibility increased from 46 to 72% (restricted intake, limited supplement). Thesodium content of the treated straw was 2% and dry matter losses 13%. Obviously only apartial solution to the problems associated with the Beckmann method is achieved; waterrequirement is reduced, but dry matter loss and river pollution are not eliminatedaltogether. The prospect of this modified method developing into an environmentally

acceptable and economically viable proposition is therefore poor.44. The Torgrimsby method, on the other hand, though still not extensively tested, hold much


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more promise. The easiest way to visualise the operation of this process is to considerhow it would work on a small, unmechanised scale. Three tanks are needed, each withan attached drain board (figure 1). Tank A contains 1000 l of a 1.5% NaOH solution inwhich 100 kg straw in bundles or bales is soaked. The first rinsing tank B contains 2000 lof water and the second rinsing tank C also contains water (1000 l). Tank B is twice as

long as tanks A and C (see top view). To the right of each tank in the diagram is asloped drainboard (a, b and c). The straw could be lifted in and out of the tanks by handor with a hand block-and-tackle on an overhead rail. The daily sequence of operations isas follows:

Figure 1. Arrangement of treatment tanks for treatment by the modified Beckmann

(Torgrimsby) method. Straw is moved from tank to tank--refer to paragraph 44.Time Operation

07:00Remove treated straw from A and place on a to drain (the straw was placed in A the day before at12:00).

08:00Remove drained treated straw from a and place in B. Place fresh (dry) straw (100 kg) in B aswell.

12:00 Make up NaOH concentration of A by adding about 4 kg NaOH. Remove fresh straw from B and

place in A. Remove treated straw from B and place on b to drain.13:00 Remove treated straw from b and place in C.

16:00 Remove treated straw from C and place on c to drain.17:00 Transfer 300 l of water from C to B to make up the volume of the latter (the 100 kg fresh straw

removed 300 l water earlier).

18:00 Wash treated straw on drainboard C with 300 l fresh water by pouring the water over the straw(This runs into C, thus making up its volume). After this final washing, treated straw is ready to


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feed.

45. The foregoing is intended as an example; numerous variations are possible. Theessential features are:

1. Soaking for 19 hours in a treatment solution containing 15 kg of NaOH/100 kg straw

as in the Beckmann method

2. the alkali washed out of the treated straw in tank B reacts with the fresh straw in thesame tank, thus pre-treating it while at the same time increasing the removal ofexcess NaOH from the treated S raw

3. a final washing with 300 l of fresh water

4. the only outgo of material from the system is 300 l water and about 4 kg NaOH/100 kgin the straw every day.

These amounts of water and NaOH are added daily. There is no loss of dry matter fromthe straw and no straw dry matter accumulates in the system.

46. The treated straw has a dry-matter content of about 20% and a sodium content on adry-matter basis of about 2% (Sundstl, 1977, personal communication). Dry matterdigestibility in vitro increased on treatment from 38 to 70. This increase in digestibility of32 units may be compared with an increase of about 17 units in the dry industrial processwhen 4 kg NaOH are used per 100 kg straw (paragraph 53).

47. It will be seen that this method retains the advantages of the Beckmann method, exceptthat the removal of excess alkali is not quite so complete, while at the same timeovercoming all the disadvantages. The increase in digestibility in vitro of 32 units and the

fact that there is only about 2% sodium present suggest that the treated straw is as highin quality as Beckmann straw, but digestibility and feeding trials must be conducted todetermine if this is so.

48. The Torgrimsby treatment process may be mechanised, as indeed the pilot plant at theUniversity of Norway is. The following description is only an example of the possibilities.Four tanks are needed, two treatment tanks and two auxillary tanks (figure 2). The strawremains in one of the two treatment tanks throughout the process, the treatment solutionand washing water being moved from tank to tank by gravity and by pumping. Onethousand litres of treatment solution (1.5% NaOH per 100 kg straw) and two lots of washwater, also in a proportion of 10:1 are employed. The daily sequence of operations is:

Treatment solution is drained from tank A to tank C.


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Figure 2. Arrangement of treatment tanks for treatment by the modified Beckmann(Torgrimsby) method. NaOH solution and wash waters are transferred from tank totank-refer to paragraph 48.

07:00 Starting position: Straw is soaking in treatment solution in tank A, having been placed there theprevious day. Wash water I (first wash water) is in tank B and wash water II (second wash water)

is in tank D. Tank C is empty.08:00 Fresh straw is put into tank B. Wash water I in B is then pumped to tank A where it is

continuously sprayed over the treated straw and recycled back to B.12:00 Wash water I is retained in tank B. Wash Water II is pumped from tank D to tank A. Wash water

I is drained from tank B to tank D. Treatment solution is pumped from tank C to tank B and its

strength made up by adding fresh NaOH.15:00 Some of wash water II in tank A is drained into tank D to make up the volume of wash water I,

and the remainder is drained into tank C. Sufficient fresh water to make up the volume of washwater II is sprayed on the treated straw in tank A and allowed to drain into tank C. The treatedand washed straw in tank A is now ready to feed.

07:00(next day)

The starting position is: Straw is soaking in treatment solution in tank B, wash water I is in tankD and wash water II is in tank C. Tank A is empty. The day's operations begin by pumping wash

water I from tank D to tank A and draining the treatment solution from tank B to tank D. Freshstraw is then placed in tank A and the sequence of operations of the previous day proceeds.

With such mechanisation the process could be scaled up to almost any size, or at least tothe size of the present-day co-operative Beckmann treatment plants.

Chemical treatment-dry methods

49. The development of dry chemical methods of straw treatment was also approached frompoint of view of improving upon the Beckmann method. The improvement was that thetreated straw is not washed. Consequently only as much NaOH can be used as will notunduly disturb the animal system. This level of NaOH has been found to be about 5kg/100 kg straw. Thus, while, the problems of dry-matter loss and river pollution aresolved by the dry method, the benefit from the use of a high alkali: straw ratio (i.e., a largeincrease in digestibility) had to be foregone. By applying heat and pressure some of thisloss in the degree of improvement in digestibility can be recovered, but the most

efficiently dry-treated straw under the best circumstances is still inferior to the bestwet-treated straw in digestibility. Moreover, sodium pollution is not eliminated, but only


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occurs in a more diffuse form when straw is treated by the dry method. On the otherhand, a very great advantage of the dry method is that it can be industrialised, as indeed ithas been. The wet methods can only be used on a farm or local community scale, andeven then the labour requirement to treat and feed wet-treated straw is a distinctdisadvantage in Europe and North America where labour is expensive.

50. The subject of the health of livestock fed on dry-treated straw has been discussed byJackson (1977). In general, animals suffer no stress if the diet contains less than 4% ofNaOH on a drymatter basis. This corresponds to 2.5% sodium in the diet.

Industrial process

51. Scientists at the Biotechnical Institute at Kolding in Denmark have developed a factorymethod for the treatment of straws and have built a successful pilot plant. Thisdevelopment work has been described by Rexen et al. (1975a) and by Rexen et al.(1975b). These publications are recommended for a detailed understanding of the factorymethod. Only a brief description will be given here.

52. A simple process-flow diagram of a straw processing factory is given in figure 3. It is acomposite of the designs of the several commercial plants visited by the consultant. Thecapacity of these plants is 45 tonnes of straw treatment per hour. Straw is delivered tothe plant as bales which are unloaded on to a concrete apron. They are then pushed by atractor with a front-mounted loader on to a conveyer leading to a tub grinder, or lifted andplaced directly into the grinder. Bale strings (sisal or plastic) are not removed but areprocessed with the straw. From the tub grinder, the straw is elevated to an intermediateholding bin. This bin acts as a buffer to even out variations in rate of intake. In someplants and automatic switch stops the intake conveyor when this bin fills to a certain level;the conveyor is again switched on when the level falls. Again in some plants, but not all,

the straw is dried to about 13% moisture content, if necessary, by electric heating coils inthe elevator between the tub grinder and the intermediate holding bin. The heating coilsare operated automatically by a sampler and moisture tester in the system at a point justbefore the treater mixer. By drying the straw the throughput of the plant is kept uniformand near maximum. In those plants which do not dry the straw, throughput fluctuateswidely with the moisture content of the straw. In the moist climate of Northern Europe,straw delivered to the factory usually has a moisture content of about 20%, if not rainedon, but there is a wide variation and plant output can be reduced considerably at highermoisture contents. Against this loss is, of course, the saving in heating costs. Aside fromthe question of throughput, straw with a moisture content of more than about 23% heatsup less in the pellet press and forms poorlycompacted pellets. From the intermediate bin

the straw goes to a hammer mill for milling in some plants, or directly to the alkali treaterin others. While there is a lack of evidence for a significant nutritional or economic benefitfrom grinding (paragraph 27), ground straw may be preferred if the treated straw issubsequently to be used in commercial concentrate mixes. Equally dense pellets can bemade from milled as from chopped straw, though more power is needed to make a givensize pellet from chopped than from milled straw; 8 mm diameter pellets are commonlymade from milled straw and 1625 mm pellets from chopped straw. If the straw hasbeen milled it is blown into a cyclone and from there it passes into the alkali treater;otherwise it passes directly to the alkali treater from the intermediate holding bin. Justbefore entering the treater, the straw passes over a band weigher which regulates therate of addition of the alkali solution. Alternatively, the weigh band is placed after thepelleter. The treater in most factories is of the type developed at the Biotechnical Institute,

Kolding and has been described by Rexen et al. (1975a). It has been designed to ensurea uniform application of the alkali solution to the straw when the rate of application is only


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1015 l (of a 3045% solution of NaOH) per 100 kg straw. Simpler ways of applying thealkali are in use in some plants-for example, the alkali solution is dribbled on the strawpassing through a screw conveyor--but mixing of lye and straw is less uniform andefficiency of alkali usage is poorer. Further, a black gum-like cake develops on the innerwalls of the conveyor and on the screw thus reducing throughput. From the treater, the

straw is conveyed to the pellet mill. Pelleting increases the density of the straw fromabout 50 to 500 kg/m3. It also causes heating (due to friction) of the straw to about 90.The heating and pressure to which the straw is subjected increases the effectiveness ofthe treatment (see figure 4). Aside from a simple effect on the rate of chemical reactionsoccuring in straw, pressure in the press probably also causes an immediate andcomplete penetration of the alkali into the straw particles. Heating the alkali solution andadding steam in the pellet mill give a small further increase in digestibility, but are notapparently worthwhile in practice. A very firm pellet is obtained as the cohesiveness ofthe straw particles is increased by NaOH; molasses is not needed as a binder. Thepellets are finally cooled and stored. In some factories the pellets are left hot for 1520minutes after coming from the press before being cooled in the pellet cooler becauseexperience has shown that they sometimes heat up again in the store if cooledimmediately; apparently the reaction between NaOH and straw is not always completewhen the pellets leave the press. Factories which produce pure, treated-straw pellets,sell them to feed compounders who grind them up and include them in conventionalconcentrate mixtures. A limited amount of these pellets are sold to farmers. In otherplants, however, the treated straw is used as only one ingredient in a complete pelletedfeed. In these plants, therefore, molasses and other feedstuffs (cereals, brans, oilcakes,etc.) are added to the treated straw before it is pelleted. Where this is done, effectivenessof the treatment of the straw is reduced (Rexen, personal communication--1977), but thisadverse effect can be counteracted to some extent if the alkali solution is heated to 90before being applied and steam is injected into the mixture when pelleting.

Figure 3. Process flow diagram of straw treatment by the industrial process (refer toparagraph 52)

53. The digestibility in vitro of 88 samples of straw processed in the Kolding pilot plant usingdifferent amounts of NaOH from 0 to 7 kg/100 kg of straw has been determined. Simple

linear regression analysis of this data has yielded the following equation: Y= 49.27 + 4.28X, where Y is digestibility in vitro and X is the kg of NaOH used per 100 kg straw (Rexen


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et al., 1975a). Thus the use of 7 kg of NaOH increases potential digestibility by about 30percentage units. Higher levels of NaOH than 7 kg may not give further increases judgingby the results of the experiment of Ololade et al. (1970) (table 10--compare figures for 8and 12 kg NaOH for 80 and 5 minutes). In digestibility trials with animals in whichfactory-treated straw has formed 70% or more of the test diets, digestibility has increased

with increasing levels of alkali upto only 45 kg NaOH (Rexen and Thomsen, 1976; Ali etal., 1977), presumably because the high sodium content and alkalinity begin to impairphysiological function of the animal. At a level of 4.5 kg alkali, which has beensubsequently adopted in most commercial plants, digestibility in vitro is increases by 20percentage units. In vivo increases were 16 units in the two experiments referred toabove. Factory-treated straw has a sodium content of about 2.7%. pH is above 10 andtitratable alkalinity is equivalent to 12 kg NaOH.

54. A number of feeding trials have been conducted with factorytreated straw (Rexen et al..1975a: Andersen. 1977: Bowerman, 1977; Wilson and Brigstock; 1977). In many of themonly one diet containing a proportion of treated straw was fed. In two, treated straw wassubstituted for other components of the diet. One of these trials was with milking cows,

but the data on actual milk yields is not given. In another, with beef animals, feed intakewas not measured. These substitution trials thus provide little concrete information whichcould be used to assess the usefulness of factory-treated straw. In only two trials weretreated and untreated straw compared. In one, a trial with growing bulls fed 30% strawdiets, no difference in weight gain was found. Because of the high proportion ofconcentrates in the diets in this trial, there may not have been any difference indigestibility between treated and untreated straw. In another trial, one with growing heifersfed diets containing 60% straw, the untreated-straw group gained at a rate of 0.67 kg/dayand the treated straw group at a rate of 0.79 kg/day. This data gives an indication of thevalue of treatment, but does not provide any information that will help in deciding whetheror not farmers could use treated straw in a conventional hay/silage and concentrate diet

for heifers. A large proportion of the production of straw-treatment plants in Europe ispresently being used as an ingredient in commercial concentrate mixtures at rates ofbetween 5 and 20% of the mixtures. There is no information to date on the value oftreated straw used in this way.

Figure 4. The effects of time and of pelleting on the digestibility of straw treated by theindustrial process (refer to paragraph 52).


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Source: Rexen et al., 1975.

55. Many experiments have been done in which dry-treated straw has been neutralized withacid before feeding it. In most of these experiments this was done only on theassumption that it would improve the feeding value of the treated straw. A few

comparisons have, however, been made between unneutralised and neutralised, treatedstraw. Rexen et al. (1975b) fed cows at restricted levels on factory-made straw pellets(containing only urea and mineral supplements) and similar pellets which had beenneutralised with HCl. The straw pellets were presumably made in two stages in order tospray the HCl on and mix the supplements. Organic-matter digestibility increased by 3percentage units and palatability, assessed by eating behaviour, was improved. Thesame pattern was also observed when the straws were mixed with concentrates in aratio of 1:1. Junker and Pfeffer (1976) found an increase in intake of factory-made treatedstraw (5% NaOH) of about 5% by neutralising with 5 l of propionic acid per 100 kg straw.Greenhalgh et al. (1973) reported, on the other hand, that farm-scale, daily-treated strawneutralised with propionic acid was no better than un-neutralised straw in an experimentwith sheep fed ad libitum. Raine and Owen (1976) fed sheep ad libitum on alkali

spray-treated straw (3.5, 7.0 and 10.5 kg NaOH/100 kg straw) prepared and fed dailywhich was unneutralised or neutralised partly or completely with HCl. Concentratesupplementation amounted to 20% of the diet. Neither intake nor digestibility weresignificantly affected by neutralisation at any level of treatment. Thus there does not seemto be sufficient improvement in feeding value to warrant the extra expense ofneutralisation. It may also be added that the utilisation of treated straw, as it is usually fedin Europe, would likely be improved by making it more alkaline and not less (paragraph62).

56. A variation on the factory process using NaOH has been developed in the GermanDemocratic Republic (Bergner et al., 1976; Bergner et al., 1974a, 1974b and 1976; Muller

and Bergner, 1975; Muller et al., 1976). Sodium hydroxide is not used; urea is mixed withthe straw at a rate of 2% before being pelleted. If the temperature during pelleting isincreased to about 150, the urea is decomposed and the NH3 released reacts with the

straw, increasing its digestibility and nitrogen content. In one experiment (Bergner et al.,1974b) the organic-matter digestibility (by sheep) of chaffed straw was increased from 38to 52 by this process. Organicmatter intake (from the straw part of the diet only)

increased from 10 to 29 g/kg W0.75. In a milking cow experiment (Bergner et al. 1976)untreated straw or straw treated with 2% urea and 2% NH4 CO3 were fed as the sole

roughage and in a third diet hay and roots were fed as roughage. The performance of thecows(yield level 615 kg milk/ day) on the treated straw was as good as that of the cowson the traditional diet of hay and roots. The food intake, milk yield and fat percentage of

milk of cows on untreated straw fell in comparison. Crdinary pellet presses do notdevelop sufficient heat during pelleting to decompose urea. The machines used by theseworkers presumably have smaller openings and/or thicker dies and accordingly, a higherpower requirement. The method looks promising, but the consultant does not haveenough information to assess its practicality or economic feasibility. Ammonia is, ingeneral, less effective than NaOH, being a weak alkali (see paragraph 80), but does addextra nitrogen to treated straw at the same time as the straw is treated and does notcause pollution).

Farm-scale treatment

57. Farm-scale treatment methods are those that can be used on the individual farm. Theyare simple and equipment costs can usually be paid by the individual farmer. These


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costs vary from a few (US) dollars for a garden sprinkling can and a hay fork to about $10,000 for one of the Danish farm machines. The methods vary in their effectiveness andthe reasons for this will be highlighted in the following paragraphs. There appears to begreat opportunity for further improvisation; a few suggestions will be given in this reportitself.

Daily treatment and direct feeding

58. Dry straw is sprinkled or sprayed with a dilute NaOH solution so that it is uniformlywetted. It is desirable to feed the straw the day after it is treated as digestibility increasessignificantly with time over the first 24 h after treatment (Ololade et al., 1970; Owen, 1978;fingerling and Schmidt, 1919). A fresh batch is prepared every day. The operation may bedone by hand where only a few animals are to be fed using a sprinkling can and_a_fork toturn the straw whilst it is being sprinkled. For complete and uniform wetting, experiencesuggests 200 l of solution per 100 kg straw. If a pressure sprayer is used this can bereduced to 100 l. For treating larger batches of straw a horizontal feed mixer or amixer-trailer designed to mix silage and concentrates may be fitted up with a pump and

spray nozzles. In this case uniform wetting can be achieved with 50 l of solution. Otheringredients in the diet can subsequently be mixed with the straw in the same mixer. Otherequipment might be devised. For example, a specially-designed screw auger with spraynozzles inside would give a continuous flow of treated straw.

59. This method is the simplest of all the farm scale methods, but is unfortunately lessefficient. This is clear from the results of in vitro studies. Ololade et al. (1970) treatedstraw with an initial digestibility of 42% with 4 g NaOH/100 g straw (table 10). Digestibilityincreased to 54 when kept at 23 for 24 hours, but to 60 when heated to 80 for only 15minutes. In the industrial process (paragraph 52) and the bulk treatment and stackingmethod on the farm (paragraph 71) both, a similar increase in digestibility in vitro occurs

as a result of the heating the straw is subjected to following spraying with alkali.Straw-treated by the dailytreatment, dry method has never been compared with theseother methods in a single digestibility trial with animals, and comparisons among trialsare difficult. An attempt may however be made. Straw treated daily with 45 kg NaOH/100kg fed ad libitum with limited concentrates has rarely been found to have increased indigestibility by more than 10 percentage units. In the experiments of Rexen andVestergaard Thomsen (1976) and Ali et al. (1977), however, the factory-treatment ofstraw increased digestibility by 16 units when fed ad libitum to sheep in diets containing30% concentrates. To achieve this degree of improvement in digestibility with thedaily-treatment method, much greater amounts of NaOH are apparently needed. In anexperiment by Fernandez Carmona and Greenhalgh (1972) in which sheep were feddiets containing 92% straw treated with 8 kg NaOH/100 kg, digestibility increased by 16units. In a later experiments (Greenhalgh et al., 1976; Pirie and Greenhalgh, 1977) withstraw fed in lamb and beef fattening diets at levels of 50 and 40% the organic-matterdigestibility of the straw was increased by 18 and 20 units, respectively, when treatedwith 8 kg NaOH/100 kg. Even in this latter experiment, however, digestibility increasedonly 2.252.5 units/kg NaOH compared to 3.9 in the experiments of Rexen andVestergaard Thomsen (1976) and Ali et al. (1977).

60. Straw treated by this method is moist, has a pleasing yellow colour and a smell of causticsoda. Animals eat it readily and when fed ad libitum usually eat 1020% more of it than ofuntreated straw. The pH is 10 or above. Sodium content increases approximately 0.6 gpercentage units for every 1 kg NaOH/100 kg added. When treated with 45 kg

NaOH/100 kg, titratable alkalinity will be equivalent to 12 kg NaOH and at 8 kg theamount will be about 4 kg (Chandra and Jackson, 1971; Piatkowski et al., 1974;


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Fernandez Carmona and Greenhalgh, 1972; Rexen, Isrealsen, Busk andWaagepetersen, 1975).

61. The results of a number of experiments have shown that in diets where straw constitutes70% or more of the diet, the least amount of alkali that will give the maximum increase in

digestibility is in the range 36 kg/100 kg (see review by Jackson, 1977). In a more recentexperiment in which treated straw was mixed with berseem forage in a ratio of 1:1 on adry-matter basis, digestibility increased significantly upto a level of 9 kg NaOH/100 kgstraw (Naik and Singh, private communication --1977). It would thus appear that thepotentially higher digestibility of straw treated with more than 6 kg NaOH can be realisedin diets in which the s traw, with its high alkalinity and sodium content, is diluted with otherfeeds. Since even this high level of alkali gave economical increases in growth (ofheifers) (table 16), it is suggested by the consultant that NaOH treatment levels canprofitably be increased to 79 kg where straw constitutes only 50% or so of the diet.

Table 15. The effect of dry treatment of straw (daily treatment method) with 8kg NaOH/100 kg on the performance of lambs, beef steers and milking cows

Dry-matter

intake, kg

Empty body

weight gain,

kg

Milk

yield,

kg

Fat

content,

%

Total

solids, %

LAMBS (36 kg initial weight)

Untreated straw

diet(50%concentrates)

0.56 0.08

Treated strawdiet

(50%concentrates)

0.85 0.14

STEERS (300 kg initial weight)

Untreated strawdiet

(60%concentrates)

8.60 0.78

Treated straw

diet(60%

concentrates)

9.67 1.03

All concentratediet

7.88 1.16

COWS

Untreated straw

diet(50%concentrates)

10.8 17.6 3.54 12.27

Treated strawdiet

(50%concentrates)

13.4 19.0 3.74 12.82

Source: Greenhalgh et al. (1976) for lambs and cow s; Pirie and Greenhalgh (1977) for steers

62. Not only are higher levels of NaOH feasible in mixed straw diets, but may even be


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essential if concentrates constitute an important part of the diet (i.e., more than about40%). Levy et al. (1977) fed high-concentrate diets (6070% concentrates and 3040%straw) to fattening bulls. Straw treated with 4 kg NaOH/100 kg was very little better thanuntreated straw in terms of animal performance, but the straw treated with 8 kg NaOHwas considerably better. Greenhalgh et al. (1976) and Pirie and Greenhalgh (1977) fed

sheep and beef cattle on barley-based concentrate diets containing 5060%concentrates and 4050% straw. Treatment of the straw resulted in a large increase inorganic matter digestibility (18 and 20 units, respectively); intake and weight gain werealso improved markedly (table 15). Earlier it was pointed out that such increases shouldnot always be expected with high-concentrate diets (paragraph 23). The success ofthese experiments appears to be due to the fact that the straw was treated with 8 kgNaOH rather than 45 kg. Depressed straw digestibility is caused by a lowering of rumenpH by the rapid fermentation of starch. It can only be supposed that in these experimentsthe high level of titratable alkalinity (unreacted NaOH) acted decisively to prevent a fall inrumen pH. Rumen fluid pH was not measured in these experiments. Incidentallyexperience has shown that straw treated with 8 kg NaOH should be fed mixed with theother ingredients in the diet and not separately, as it is somewhat unpalatable.

63. The use of Ca(OH)2 in treating straw has always been of interest, as already mentioned

(paragraph 41), because it is cheaper than other alkalis. With spray-treated materialCa(OH)2 has consistently be found inferior to NaOH (reviews by Jackson, 1977 and

Klopfenstein, 1976). Gharib et al. (1975b), however, found that when treated popular barkwas ensiled for 150 days Ca(OH)2 was as effective as NaOH. Wilkinson and Gonzalez

Santillana (1977) ensiled treated barley straw for 90 days and found Ca(OH)2 2/3rds as

effective as NaOH (see also paragraph 75). Coming back to the daily treatment andfeeding of straw, mixtures of 1 kg Ca(OH)2 and 3 kg NaOH when used to treat 100 kg

straw have been found in several experiments (review by Klopfenstein, 1976) to be

superior to 4 kg NaOH in terms of the performance of growing lambs and calves. It is notknown whether this is due to the effect of the chemicals on the digestibility of straw or anutritional effect of the added calcium.

64. A variation of the simple spray treatment described above is the Boliden method. Thismethod has been developed by a private company in Sweden, Nid Boliden AB ofHelsingborg. Straw is sprayed with an alkali solution and then with an acid solution in aspecially designed apparatus. The unit seen by the consultant at the AgriculturalUniversity of Norway could treat a 500 kg of baled straw per day. A schematic diagram ofthe apparatus used is given in figure 5. In the morning a fresh batch of baled straw (500kg) is placed in the treatment chamber on the mesh floor. An NaOH solution sufficient to

provide 22.5 kg NaOH (4.5 kg/100 kg straw) is pumped into the funnel under thechamber. The water supply to the funnel is then turned on. As the funnel begins to fill up apump starts and pumps the solution on to the straw through spray nozzles in a travellingoverhead spray boom. The straw becomes saturated in about 1 1/2 hours after whichexcess solution drains back into the funnel and is recirculated. A float value in the funnelcontrols the flow of water into the funnel. About 1800 l of solution is made and atequilibrium all but about 100 l is in the saturated straw. A charge of 22.5 kg of Ca(OH)2 is

also introduced into the system as a suspension in the water. The treatment solution iscirculated for a 4 hours. The saturated straw is then allowed to stand overnight (about 16hours). Seven l of an acid mixture is then pumped into the funnel and circulation resumedfor another 2 hours. The acid mixture is a patented product sold by the company. Itcontains HC1 and H

3PO

4. The pH of the straw is brought down to 89. A further hour or

so is allowed for draining and then the straw can be removed and fed. The apparatus can


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then be loaded with fresh straw.

Figure 5. Chamber for treatment of straw by the Boliden method (refer to paragraphs 64and 65).

65. The treated straw is of course saturated (20% dry-matter approximately) and in thisrespect resembles wet treated straw. Chemically, however, it resembles dry-treatedstraw neutralised with mineral acid. It has sufficient calcium and phosphorus to eliminatethe need for the usual mineral supplements. The straw is being evaluated at theAgricultural University of Norway and at the moment very little is known about its feeding

value. Digestibility in vitro of grab samples from untreated and treated bales has beendetermined; the values are 45 (3950) for untreated and 68 (6575) for treated (Sundstl,private communication-1977). It is not possible to assess the effectiveness of thismethod from this limited data. Feeding trials will have to be done. It is suggested thatsuch trials aim at distinguishing among the effects of NaOH, Ca(OH)2 and acid. The

method should also be compared in a single trial with the simpler daily-treatment methoddescribed in the preceeding paragraphs using 4.5 kg NaOH.

66. Considerable experimentation with ammonia treatment has been done in the last fewyears. The stacking method in which anhydrous ammonia is used is described inparagraphs 7983. Development work on the treatment of straw in air-tight tanks has

been carried out at the Biotechnical Institute at Kolding (Rexen, 1977; Waagepetersenand Vestergaard Thomsen, 1977). A cylinderical tank which can accomodate 80 bales


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has been tested. Anhydrous ammonia (3.5 kg) is introduced and circulated by a fan. Thetank is insulated to conserve the heat produced by the chemical reaction of the ammoniawith the straw, which is considerable. A five-day treatment period has been found to givean increase in enzyme digestibility (of barley straw) of 15 units (27 to 42) whichcorresponds to an increase in in vitro organic matter digestibility of 14 units (5468) (B.

Rexen, 1977). The average temperature inside the tank during the first 24 hours was 38.In another trial with the same tank steam was introduced to raise the temperature to anaverage of 70. The treatment period lasted only one day. Calculated dry-matterdigestibility in vitro increased from 57 to 75. A tank manufactured by a commercial firm inDenmark, which is undergoing testing at the Biotechnical Institute at Kolding, is fitted withelectric heating coils to maintain a uniform temperature of 70 for 24 hours since theearlier test showed that, in order to treat one batch effectively every day, this temperatureis needed. Something will be said about the feeding of ammonia-treated straw in a laterparagraph (81).

67. A great many digestibility and feeding trials have been carried out with straw treated dailywith NaOH and fed directly. The range in increases in digestibility in vitro of published

experimental results from some 3 dozen digestibility trials is 0 to 22 percentage units.Different levels of NaOH and different types of test diets were used; in some ad libitumfeeding was followed and in others restricted feeding; different types and ages of animalswere used; in some cases the treated straw was neutralised; and many more factorscould have contributed to this variability. It is, however, desirable, and reasonably possiblealso, to indicate the expected extent of improvement with ad libitum feeding ofstrawcontaining diets. These would be 10 units for straw treated with 45 kg NaOH/100kg straw, allowed 24 h curing time and fed in diets containing 7080% or more of straw.This 10 units refers to an increase in derived straw digestibility, calculated by assumingthat the digestibility of the other components of the diet are the same for the dietscontaining treated and untreated straw. In diets containing 4060% other feeds

(concentrates and/or forage), straw treated with 79 kg NaOH/100 kg should be expectedto increase in digestibility by 17 units if the diets are fed ad libitum and the s traw is curedfor 24 hours.

Table 16. The effect of dry treatment (daily treatment with NaOH) of wheatstraw on the performance of dairy heifers fed a wheat straw-berseem diet

Untreated straw Treated straw*

Dry matter intake, g/kg W0.75 109 109

Organic matter digestibility, % 59 67

Liveweight gain, kg 0.49 0.64Daily feed cost, Rs./animal 1.70 2.13

Feed cost/kg gain, Rs. 3.47 3.33

Days to gain 100 kg 204 156* Straw spray- treated (farm scale) w ith 9 kgNaOH/100 kg straw and fed immediately.

Source: Naik and Singh, private communication--1977.

68. Examples of the results of some production trials with daily treated (NaOH) are given intables 1517. An economic analysis of some of these diets is taken up in paragraph 88.

Table 17. The performance of calves on untreated and treated straw diets(Source: Singh et al., 1975.


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Untreated straw plus

groundnut cakeTreated* straw plus

groundnut cake

Straw consumption,kg/day

4.5 6.0

Concentr.

consumption, kg/day 0.8 1.0Gain, kg/day 0.25 0.42

Total feed costs,Rs./day

0.95 1.39

Feed cost/kg gain, Rs. 3.80 3.31

Days to gain 100 kg 400 238* Straw spray- treated (farm-scale) w ith 3.3 kg NaOH/100 kgstraw and Ted immediately.

Bulk treatment followed by stacking

69. On many farms there may be reasons why the bulk treatment of straw for a wholeseason or for a month or so is more attractive than daily treatment. If the straw is treatedin bulk with NaOH there can be a bonus of enhanced effectiveness of the added alkali.Capital costs of equipment and structures may be higher however.

70. The Danish farm machines manufactured by Taarup and by J.F. Fabriken produce atreated straw similar to that emerging from the NaOH treater in the industrial process.The bales are shredded, a concentrated NaOH solution (usually 27%) is sprayed on (5 kgNaOH/ 100 kg straw) and then the straw passes through a long mixing chamber in whichthe straw is squeezed or rubbed between an intricate series of rotating and stationaryblades. The penetration of the NaOH is thus facilitated. The treated straw is then blowninto a pile. If the pile is big enough (minimum 34 tonnes) the treated straw will heat up toa temperature of 8090. The heating is caused by the accumulation of the heat liberated

by the chemical reactions between the NaOH and the straw. The temperature reaches apeak during the first 3 days and then declines for a further 15 days or so to ambienttemperature. As a result of this heating, moisture evaporates leaving the straw dryenough to store if the initial moisture content of the straw does not exceed 17% beforetreatment. If initial moisture content is more than 17% there will be less heating andinsufficient drying leaving a material which will go mouldy or which can heat up again dueto bacterial fermentaction; such material appears to behave, in fact, like damp hay. Thestack must be made at a place where it is open on at least one side and at the top toensure adequate drying. Straw treated in this way should not be put in a silo because itwill probably overheat and become a fire hazard.

71. The treated straw is dry, has an attractive golden colour and smells slightly of NaOH. Theincreases in digestibility resulting from this treatment are shown in table 18. These valueswere determined by the staff of the Biotechnical Institute, Kolding and they have beensupplied to the consultant by Mr. Peder Kjeldsen and Mr. Niels Arne Pedersen of J.F.Fabriken, Snderborg. The increase in digestibility in vitro with 5 kg NaOH/100 kg straw isidentical to that of factory-treated straw. It is obvious that the heating that occurs in thestack after treatment is vital to this high efficiency. The digestibility increase is not uniformthroughout the stack but varies with the extent of temperature rise, which is, of course,most in the centre and less near the surface. The values shown in table 18 are weightedaverages. Samples of more than 50 lots of farmer-treated straw have been analysed andhave averaged 68% organic matter digestibility in vitro (Kjeldsen and Pederson, privatecommunication--1977).


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Table 18. The digestibility of untreated and treated straw (5 kg NaOH/100 kgstraw) (J.F. Fabriken machine)

Enzymedigestibility, %

Calculated

organicmatterdigestibility in vitro,

%*

Titratable

alkalinity,g of

NaOH/100 g stras

Untreated straw 18 48 0

Treated straw on

leaving machine35 62 2.3

Treated straw fromstack 15 days

after treatment

43 69 0.4

* Calculated using the regres sion equation :Y = 33.24 + 0.83 X, w here Y is organic matterdigestibility in vitro andX is enzyme

digestibility(B. Rexen, 1977) .

Source: J.F. Fabriken, Snderborg, Denmark--1977.

72. As is the case with factory-treated straw, bulk-treated and stacked straw has rarely beencompared with untreated straw in a feeding experiment. One experiment is known tohave been done with milking cows (Kristensen, private communication--1977) and onewith growing heifers (Andersen, 1977). In the former, straw was fed ad libitum with fixedamounts of molasses (5 kg) and a concentrate mixture (6.4 kg). Treatment increased theintake of straw from 5.5 to 7.6 kg and fat-corrected-milk yield from 20.4 to 22.2 kg. In thelatter trial heifers were fed treated barley straw ad libitum and 3 kg other feeds. Strawintake increased from 3.4 to 3.6 kg and weight gain from 0.70 to 0.78 kg/day. Neither ofthese results is impressive, but the type of diet in which the straw was fed was perhapsnot conducive to a larger response from treated straw. The experiment on milking cowsis commented upon further in paragraph 82.

Bulk treatment followed by ensiling

73. The results of several experiments have shown that straw spray-treated with 60120 1 ofNaOH solution and ensiled can be stored for upto one year. There is no microbialfermentation and the straw remains stable due to its high pH. The digestibility does notincrease due to ensiling (Wilkinson and Gongalaz Santillana, 1977 b). The temperature ofthe ensiled mass rises (Wilkinson, private communication--1978), but probably notenough (due to the high water content of the straw) to reach a temperature of about 80degrees (see table 10) which would increase the effectiveness of the alkali. At ambient or

even somewhat higher temperatures, digestibility does not increase after the first 24 h(Braman and Abe, 1977; Gharib et al., 1975a; Gharib et al., 1975b).

Table 19. Performance of lambs fed wheat straw diets *

DietDry-matter

intake, g

Liveweight

gain, g

Feed:

gain

ratio

Derived

organicmatter

digestibility, %

Untreated

straw908 36 25.0 49

Treated**

straw1226 160 7.6 60


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* 70% straw and 30% concentrate supplement

** straw spray- treated w ith 4 kg NaOH/100 kgstraw

** assuming a constant digestibility of 90%for the concentrate supplement.

Source: Hasimoglu et al., 1969.

74. Treated, ensiled straw has given very good results in several production trials. On dietscontaining 70% or more of treated straw liveweight gains of lambs have been increased4_fold (tables 19 and 20). The results of another feeding experiment with calves (table21) show how treated and ensiled straw can be used to extend good quality grass silagein rearing calves. Although the treated straw in this case was not as digestible as thegrass silage, a diet containing 2/3 rds treated straw still gave weight gains of more than0.5 kg/day. Klopfenstein (1976) summarised the results of 3 experiments with calves inwhich maize silage was compared with treated, ensiled maize husks (table 22). Theresults of these latter two trials as well as those of piatkowski et al. (1974b) (described inparagraph 77) are particularly useful as they indicate the feeding value of treated straw inrelation to other roughages silages in this case--and give an indication of how it could beused in conventional high-roughage diets on which young stock is fed. An economic

analysis of the data in table 22 has been done by the author and will be presented inparagraph 93.

Table 20. Performance of lambs on maize stover diets *

Diet Dry-matter intake, g Liveweight gain, g Feed gain ratio

Untreated stover 950 18 25.3

Treated stover** 1380 89 7.4

* Diets contained 25% of a supplement basedon brew ers ' dried grains and urea

** Straw spray-treated w ith 3 kg NaOH and 1 kgCa(OH)2/100 kg straw and ensiled

Source: Lamm, 1976.

75. The ensilling of treated straw seems to offer a possibility of using Ca(OH)2. Many

experiments have shown that when Ca(OH)2 is sprayed on straw it has very little effect

on digestibility if the straw is fed the same day or the next day (Gharib et al., 1975b;Verma and Jackson, 1975). Gharib et al. (1975 b), however, found it to be as effective asNaOH if the treated material (poplar bark) was ensiled for 150 days. With a 90-dayensilling period Ca(OH)2 was about 2/3rds as effective as NaOH (Wilkinson and

Gonsalez Santillana, 1977 a). The advantage of Ca(OH)2 over NaOH is, of course, its

lower cost.

76. A special situation in which the ensilling of treated straw may be useful is in Italy. Paci(1955) reported that rice straw is still green at harvest in the autumn and that there isinsufficient sunny weather to dry it. He tried ensilling it with mineral acids with goodresults. Alkali treatment and ensiling might be a better alternative. All over Europe muchstraw is rained on before it can be picked up from the field. It could be successfully keptand used as a feed by alkali treating and ensiling.

77. Piatkowski et al. (1974 b) treated barley straw with 5 kg NaOH/100 kg (100 l solution) andafter 2 weeks ensiled it with green maize forage in the following proportions on a drymatter basis: 17:83 and 34:66, respectively. There was a greater acid production from

the maize during the subsequent fermentation and the amounts of residual sugars werereduced. The pH values of pure maize silage and the two mixed silages were 3.8, 4.0 and


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4.3, respectively. The organic-matter digestibility of the three silages was 69%, indicatingthat the digestibility of the treated straw was the same as that of the maize. There doesnot seem to be any advantage of this practice over mixing treated straw with maize silageat the time of feeding. By mixing the treated straw with the fresh maize at the time ofensiling rather than at the time of feeding, the benefit of the treated straw in raising the pH

of the diet was not realised; the alkalinity of the straw increased acid production from thesugars in the maize. Thomas and Wilkinson (1975) found that raising the pH of maizesilage (from 3.95 to 5.45) by adding sodium bicarbonate increased voluntaryconsumption by 12%. Thus there would seem to be a definite advantage of mixing treatedstraw and silage together at the time of feeding.

Table 21. The performance of calves on silage, treated straw andsilage-treated straw diets

Diet *Dry-matter

intake, % of LW

Organic matter

digestibility, %

Liveweight gain,

kg/day

Grass silage 2.44 74.0 0.89

Silage: straw**

(67:33 on adry-matter basis)

2.42 71.4 0.75

Silage straw

(33:67 on adry-matter basis)

2.44 71.3 0.55

Straw 1.94 67.8 0.15

SE of means 0.07 0.8 0.04* In addition to the silage the calves w ere fed ureaprills (46% N) and soyabean meal (7.2% N in the drymatter)at the rates of

2.5% of s ilage/straw drymatter and 0.3% of livew eight, respectively.

** Straw w as spray-treated w ith 7.5 kg NaOH/100 kgand ensiled for 76 days.

Source: Wilkinson and Ganzalez Santillana, 1977 b.

78. A novel approach to treating straw in the silo has been studied by Oji and Mowat (1977).They ensiled maize stover after spraying it with 10 1 of a 50% solution of urea/100 kg.Initial moisture content of the stover was 55%. All the urea was decomposed within 20days. The ammonia released would presumably react with the stover and increase itsdigestibility. This possibility should be investigated.

Table 22. Performance of calves on diets of maize silage and treated * andensiled maize husks

Maize silage diet** Treated maize husks diet***

Liveweight gain, kg 0.75 0.75

Dry-matter intake, kg 7.26 7.17

Feed/gain ratio 9.62 9.60

* Straw treated ith 3 kg NaOH and 1 kgCa(OH)2/100 kg straw

** 90% maize silage and 10% supplementson a dry-matter basis

*** 80% maize

Documents

Treating Straw for Animal Feeding