Effects of varying the degree of synchrony ofenergy and nitrogen release in the rumen on thesynthesis of microbial protein in lactating dairycows consuming a diet of grass silage and acereal-based concentrateKyoung H Kim, Jai-Jun Choung and David G Chamberlain*Hannah Research Institute, Ayr, KA6 5HL, UK

Abstract: The object of the experiment was to test the hypothesis that altering the degree of synchrony

in the ruminal release of available energy and nitrogen would affect microbial protein synthesis (MPS)

when the diet contained a high proportion of readily fermentable carbohydrate. Four lactating dairy

cows were given a basal diet of (kg DM dayÿ1) 8.0 grass silage, 4.2 barley and 1.8 groundnut meal

containing 31.4g Nkgÿ1 DM. The experiment was designed as a 4�4 Latin square with periods lasting

14 days. The treatments were (1) the basal diet given in two equal meals at 10:00 and 22:00h (BASAL),

supplemented with (2) 2.0kg maltodextrin given as a continous intraruminal infusion (CONT), (3)

2.0kg maltodextrin as two 6-h infusions starting at 10:00 and 22:00h (SYNC) and (4) 2.0kg maltodextrin

given as two 6-h infusions starting at 16:00 and 04:00h (ASYNC). All three infusion treatments reduced

(P<0.05) the concentration of ruminal ammonia relative to BASAL but only the CONT and SYNC

treatments increased (P<0.05) MPS over the level with BASAL; the value for ASYNC was the same as

that for BASAL. Lactic acid was a minor product of the ruminal fermentation with all treatments. All

three infusions reduced (P<0.05) the plasma concentration of urea and the urinary output of nitrogen

but there were no differences among the infusion treatments. It is concluded that with this diet,

containing about 30% of DM as fermentable carbohydrate, altering the degree of synchrony in the rates

of ruminal release of energy and nitrogen had a marked effect on MPS.

# 1999 Society of Chemical Industry

Keywords: grass silage; carbohydrate supplements; rumen synchrony; dairy cow

INTRODUCTIONThe current interest in synchrony of release of

available energy and nitrogen in the rumen derives

from the assumption that a lack of synchrony leads to

inef®cient microbial capture of nitrogen and hence to a

reduced ef®ciency of microbial protein synthesis

(MPS). However, there is little experimental evidence

to support the case for close synchrony of energy and

nitrogen release; indeed, owing to a compounding of

effects of changes in dietary ingredients with effects of

synchrony itself, the design and interpretation of some

experiments reported in the literature are ¯awed (see

Ref 1). The need for synchrony has been considered

specially important with diets based on grass silage, in

which markedly asynchronous rates of release of

energy and nitrogen in the rumen are held responsible,

at least in part, for the low rates of MPS that can occur

with these diets.2 However, even with a diet containing

a high proportion of grass silage, Kim et al3 failed to

show any effects of the degree of synchrony on MPS in

a controlled experiment in which sucrose was infused

direct into the rumen in different patterns.

Presumably, the apparent lack of effect of the degree

of synchrony on MPS derives from the ability of rumen

bacteria to buffer themselves against the effects of

¯uctuating supplies of available energy and nitrogen

by synthesizing intracellular storage polysaccharide

when fermentable carbohydrate is in relative excess,4

to be used as a source of ATP later in the feeding cycle

when fermentable carbohydrate is in short supply.5

However, the capacity of ruminal bacteria for storage

of intracellular polysaccharide must be limited.6 This

would imply that synchrony of energy and nitrogen

release could have more pronounced effects on MPS

with diets rich in fermentable carbohydrate because, in

these conditions, bacteria might not be able to buffer

themselves completely from marked ¯uctuations of

energy supply without exceeding their cellular capacity

Journal of the Science of Food and Agriculture J Sci Food Agric 79:1441±1447 (1999)

* Correspondence to: DG Chamberlain, Hannah Research Institute, Ayr, KA6 5HL, UKContract/grant sponsor: Scottish Office Agriculture, Environment and Fisheries DepartmentContract/grant sponsor: Rural Development Administration of Korea(Received 30 October 1998; revised version received 4 March 1999; accepted 16 April 1999)

# 1999 Society of Chemical Industry. J Sci Food Agric 0022±5142/99/$17.50 1441

for storage of polysaccharide. The lack of effect in the

previous experiment3 would then be explained by the

relatively modest level (about 15% of dry matter) of

fermentable carbohydrate in the experimental diet.

The experiment reported here was designed to test

this hypothesis. Lactating dairy cows receiving a high-

protein diet of grass silage and a barley-based

concentrate were given a supplement of maltodextrin

infused into the rumen in three different patterns

chosen to induce varying degrees of synchrony with

the ruminal release of ammonia. The results show that

with this diet, containing around 30% of readily

fermentable carbohydrate in the dry matter, altering

the degree of synchrony markedly affected MPS in the

rumen.

EXPERIMENTALAnimals and their managementFour Friesian cows in their third or fourth lactations

and each ®tted with a large rubber cannula into the

rumen were used. The cows were 9±12 weeks into

their current lactations and were housed individually

in metabolism stalls and milked each day at 08:00 and

16:00h. Food was provided in two equal meals each

day at 10:00 and 22:00h and water was freely available

at all times.

Experimental diet and treatmentsThe basal diet was 40kg grass silage, 5kg rolled barley

and 2kg groundnut meal dayÿ1, corresponding to 8.0,

4.2 and 1.8kg DM dayÿ1 from silage, barley and

groundnut meal respectively. The food offered was

completely consumed on all occasions. The metabo-

lizable energy (ME) supplied from the basal diet was

calculated to be suf®cient to support a milk production

of around 23kg dayÿ1.7 The silage was made from

perennial ryegrass (Lolium perenne) cut at an early stage

of growth and ensiled, with the addition of a

commercial inoculant (Ecosyl, Ecosyl Products Ltd,

Billingham, Cleveland, UK) at the manufacturer's

recommended rate, in a bunker silo of 60tons

capacity. The chemical composition of the silage is

shown in Table 1. The silage was reasonably well

preserved, had a low pH and an absence of butyric acid

and moderately low levels of ammonia, but it showed

signs of secondary fermentation with low concentra-

tions of lactic acid and high concentrations of acetic

acid and ethanol. The rolled barley contained (gkgÿ1

DM): total-N, 19.4; NDF, 192; ADF, 57; and starch,

622. The groundnut meal contained (gkgÿ1 DM):

total-N, 85.2; NDF, 210; ADF, 111; sugars, 93; and

starch, 64. The total diet contained 31.4g Nkgÿ1 DM.

The four experimental treatments were (1) the basal

diet (BASAL), supplemented with (2) 2.0kg malto-

dextrin (Cerestar UK Ltd, Manchester, UK) given as

a continuous intraruminal infusion (CONT), (3)

2.0kg maltodextrin given as two 6-h intraruminal

infusions starting at 10:00 and 22:00h each day

(SYNC), and (4) 2.0kg maltodextrin given as two

6-h intraruminal infusions starting at 16:00 and

04:00h each day (ASYNC). According to information

provided by the suppliers, the maltodextrin contained

a wide distribution of polymers (number average

molecular weight, 1931; weight average molecular

weight, 38650) with around 80% of the mixture

having a degree of polymerization between 6 and

450. All infusions were given in 6 litres of aqueous

solution dayÿ1 using a peristaltic pump (Watson

Marlow Ltd, Falmouth, Cornwall UK).

Experimental plan and proceduresThe experiment was designed as a 4�4 Latin square

Table 1. Chemical composition (gkgÿ1 DM unlessstated otherwise) of the silage

Dry matter (gkgÿ1)a 199

Organic matter 908

Total-N 26.5

NPN (gkgÿ1 N) 854

Ammonia-N (gkgÿ1 N) 146

Water-soluble carbohydrate 6

Neutral-detergent ®bre 544

Acid-detergent ®bre 361

PH 4.24

Lactic acid 41

Acetic acid 60

Propionic acid 5

Butyric acid 0

Ethanol 20

a By toluene distillation.

Table 2. Ruminal pH, theconcentrations of ammonia-N, lacticacid, total VFA and the molarproportions of individual VFA in therumen in dairy cows consuming a dietof silage and concentrate without(BASAL) or with intraruminal infusionsof maltodextrin given continuously(CONT), synchronously (SYNC) orasynchronously (ASYNC)a

BASAL CONT SYNC ASYNC SED P valueb

pH 6.60 6.29 6.17 6.15 0.09 0.011

NH3-N (mg litreÿ1) 211 136 162 172 8.8 <0.001

Lactic acid (mmol litreÿ1) 1.5 1.0 2.0 1.4 0.79 0.692

VFA (mmol litreÿ1) 119 125 130 131 5.8 0.246

Acetic (mmol molÿ1) 660 658 650 643 13.4 0.599

Propionic (mmol molÿ1) 184 169 189 191 15.7 0.531

Isobutyric (mmol molÿ1) 10 4 4 4 2.4 0.127

Butyric (mmol molÿ1) 119 143 132 134 4.4 0.009

Isovaleric (mmol molÿ1) 14 12 12 14 1.2 0.121

Valeric (mmol molÿ1) 13 16 13 14 0.4 0.007

a Values are means of six samples during the day in each of four cows.b Statistical signi®cance by F-test.

1442 J Sci Food Agric 79:1441±1447 (1999)

KH Kim, J-J Choung, DG Chamberlain

with 14-day periods. Samples of blood, obtained from

an indwelling jugular catheter, and rumen contents,

obtained by suction through the ruminal cannula,

were taken on day 11 at 09:30 (before feeding); 11:00;

12:30; 15:30; 18:30 and 21:30h. Samples of milk were

taken from four consecutive milkings on days 10 and

Figure 1. Variation during the 12h between the morning and evening meals in (a) ruminal pH and (b) ruminal concentrations of ammonia-N and (c) bloodconcentrations of urea-N in dairy cows consuming a diet of silage and concentrate (*) without, or with intraruminal infusions of maltodextrin given (*)continuously, (&) synchronously on (&) asynchronously.

J Sci Food Agric 79:1441±1447 (1999) 1443

Synchrony of energy and N release in synthesis of microbial protein in cows

11 and bulked to give a representative subsample. The

complete output of urine was collected into 500ml of

4M H2SO4 on days 12, 13 and 14. Urine was collected

via a bladder catheter implanted on day 11.

Chemical analysisChemical analysis of feeds, rumen contents and urine

was as described by Chamberlain et al8 and of blood as

described by Chamberlain et al.9

Statistical analysisThe results were analysed using the ANOVA directives

of Genstat 5.10 The mean values for the yield of milk

for the last ®ve days of each experimental period were

used for statistical analysis.

RESULTSDaily mean values for ruminal variables are shown in

Table 2. Ruminal pH was reduced (P<0.05) by all

infusion treatments relative to BASAL but differences

between infusion treatments were not statistically

signi®cant. Compared with BASAL, all infusion

treatments reduced (P<0.01) the concentration of

ammonia-N, the CONT treatment being associated

with a greater (P<0.05) reduction than the SYNC

and ASYNC treatments. The daily mean concentra-

tion of lactic acid was similar for all treatments.

Examination of the concentrations in samples taken

during the day (not shown) also showed a broadly

similar pattern for all treatments, with maximum

values (on average, around 5mmol litreÿ1) being

reached at 1h after feeding. The only difference

among the treatments in the ruminal concentration

Table 3. Daily output of total nitrogen and purinederivatives (PD) in urine and the calculated amountof microbial N entering the small intestine in dairycows consuming a diet of silage and concentratewithout (BASAL) or with intraruminal infusions ofmaltodextrin given continuously (CONT),synchronously (SYNC) or asynchronously(ASYNC)

BASAL CONT SYNC ASYNC SED P valuea

Total-N (g dayÿ1) 189 129 133 136 7.7 <0.001

PD output (mmol dayÿ1) 245 281 273 241 11.1 0.025

Microbial Nb (g dayÿ1) 173 204 197 169 9.5 0.025

a Statistical signi®cance of treatment effects by F-test.b Calculated using the equation of Susmel et al .23

Table 4. Concentrations of urea-N,ammonia-N, glucose and insulin inblood plasma of dairy cows consuminga diet of silage and concentrate without(BASAL) or with intraruminal infusionsof maltodextrin given continuously(CONT), synchronously (SYNC) orasynchronously (ASYNC)a

BASAL CONT SYNC ASYNC SED P valueb

Urea-N (mg litreÿ1) 211 164 174 163 11.9 0.070

Ammonia-N (mg litreÿ1) 1.4 1.3 1.4 1.3 0.13 0.452

Glucose (mg litreÿ1) 673 698 676 660 18.8 0.388

Insulin (ngmlÿ1) 0.556 0.805 0.800 0.694 0.051 0.041

a Values are means of six samples during the day in each of four cows.b Statistical signi®cance of treatment effects by F-test.

Table 5. Concentrations (mmol litreÿ1)of amino acids in the blood plasma ofdairy cows consuming a diet of silageand concentrate without (BASAL) orwith intraruminal infusions ofmaltodextrin given continuously(CONT), synchronously (SYNC) orasynchronously (ASYNC)a

BASAL CONT SYNC ASYNC SED P valueb

Histidine 13 20 18 20 4.1 0.385

Threonine 77 64 82 89 7.7 0.073

Arginine 73 54 67 61 10.0 0.369

Tryptophan 41 28 44 39 8.8 0.384

Methionine 12 10 13 13 1.3 0.150

Valine 138 123 147 138 18.8 0.673

Phenylalanine 49 40 45 43 5.0 0.395

Isoleucine 80 70 78 72 12.8 0.855

Leucine 66 53 69 64 9.1 0.431

Lysine 50 43 54 47 8.4 0.602

Aspartic acid 7 5 6 4 1.7 0.240

Glutamic acid 48 41 45 42 5.5 0.640

Asparagine 35 29 36 34 3.6 0.284

Serine 105 71 82 84 6.6 0.010

Glutamine 189 206 186 198 22.8 0.823

Glycine 377 330 366 345 48.9 0.780

Alanine 146 104 128 125 23.8 0.430

Tyrosine 52 41 56 54 8.5 0.383

Taurine 14 12 24 26 7.0 0.241

Ornithine 32 28 35 30 3.8 0.366

Total amino acids 1593 1320 1569 1520 169.0 0.428

a A composite sample from six sampling times during the day in each of four cows.b Statistical signi®cance of treatment means by F-test.

1444 J Sci Food Agric 79:1441±1447 (1999)

KH Kim, J-J Choung, DG Chamberlain

of lactic acid occurred at 8.5h after feeding, when the

concentration for the ASYNC treatment was greater

(P<0.01) than for all other treatments; respective

values (mmol litreÿ1) were 0.26, 0.25, 0.37 and 1.54

for BASAL, CONT, SYNC and ASYNC. For the

molar proportions of ruminal VFA, only butyric and

valeric acids were affected by treatment, with butyric

acid being increased (P<0.05) by all treatments

relative to BASAL and valeric acid being greater

(P<0.01) for CONT than for all other treatments.

Variations with time of sampling in ruminal pH and

ammonia concentration are shown in Fig 1. The

overall pattern of variation was similar across the

treatments for both variables but there were statisti-

cally signi®cant differences among the treatments in

the values observed at some of the sampling times. For

the prefeed (zero time) samples, pH for BASAL was

higher (P<0.05) than for ASYNC but none of the

other differences between treatments was signi®cant.

The lowest pH values were observed at 2.5 and 5.5h

after feeding and, from 5.5h onwards, pH for BASAL

was higher (P<0.05) than for all other treatments. At

5.5 and 8.5h, differences among the infusion treat-

ments also reached statistical signi®cance, SYNC

being associated with a lower pH (P<0.05) than

either CONT or ASYNC at 5.5h and ASYNC giving a

lower pH (P<0.05) than the other two infusions at 8h

after feeding. For ammonia concentrations, the pre-

feed sample showed a higher (P<0.05) value for

BASAL than for either CONT or ASYNC treatments.

One hour after feeding, ammonia concentrations on

the BASAL treatment were higher (P<0.01) than for

all the other treatments and values for the BASAL

treatment were also higher (P<0.05) than for CONT

and SYNC at 2.5h, higher (P<0.05) than CONT at

5.5h and 7h, and higher (P<0.05) than CONT and

SYNC at 8.5h.

The urinary outputs of nitrogen and purine deriva-

tives are shown in Table 3. The excretion of nitrogen

in urine was reduced (P<0.001) by all the infusion

treatments relative to BASAL but there were no

differences among the infusion treatments. The

calculated amount of microbial N entering the small

intestine was increased (P<0.05) over BASAL for the

CONT and SYNC treatments but no increase was

seen with the ASYNC treatment.

The daily mean concentrations of urea-N, ammo-

nia-N, glucose and insulin in blood plasma are shown

in Table 4. The concentration of urea-N was higher

(P<0.05) for BASAL than for all three infusion

treatments. The concentration of ammonia-N in

plasma varied little during the period between feeds

(not shown) and the mean concentration did not differ

between treatments. There were no differences among

the treatments for glucose concentrations but insulin

levels were increased (P<0.05) by all infusions

relative to BASAL and, amongst the infusion treat-

ments, ASYNC tended (P<0.10) to be associated

with lower concentrations of insulin in blood plasma

than were the other two infusions.

The concentrations of amino acids in the blood

plasma are shown in Table 5. For threonine, the

CONT treatment produced lower (P<0.05) concen-

trations than did ASYNC and values for CONT also

tended (P<0.10) to be lower than for SYNC.

Concentrations of methionine tended (P<0.10) to

be lower for CONT than for SYNC and ASYNC. All

infusion treatments reduced (P<0.05) the concentra-

tion of serine relative to BASAL.

The milk production results are shown in Table 6.

Milk yield was not signi®cantly affected by the

treatments but there were effects on the yield and

concentration of fat and protein in the milk. The

concentration and yield of milk fat were greater

(P<0.05) for SYNC than for the BASAL and CONT

treatments. All infusion treatments increased

(P<0.05) the concentration of protein in the milk

relative to BASAL. The yield of milk protein was

greater (P<0.01) for ASYNC than for BASAL and

CONT treatments.

DISCUSSIONThe object of the experiment was to test the hypothesis

that altering the degree of synchrony of energy and

nitrogen release in the rumen would affect MPS with a

diet rich in readily fermentable carbohydrate. To this

end, the present experiment used a diet containing

around 30% of DM as readily fermentable carbohy-

drate in the form of starch and sugars, double the level

used in the experiment of Kim et al.3 Lactating dairy

cows were used because we considered them more

likely to consume the experimental diet, together with

the relatively high level of infused maltodextrin,

without refusals.

A prerequisite was that the basal diet should contain

Table 6. Yield and composition of milkin cows consuming a diet of silage andconcentrate without (BASAL) or withintraruminal infusions of maltodextringiven continuously (CONT),synchronously (SYNC) orasynchronously (ASYNC)

BASAL CONT SYNC ASYNC SED P valuea

Milk yield (kg dayÿ1) 20.6 19.1 20.1 20.5 0.57 0.125

Milk fat (gkgÿ1) 38.4 39.9 45.3 42.0 2.26 0.090

(g dayÿ1) 785 761 920 892 51.6 0.074

Milk protein (gkgÿ1) 30.1 32.3 32.0 33.1 0.63 0.017

(g dayÿ1) 620 615 643 678 11.9 0.006

Milk lactose (gkgÿ1) 45.8 45.7 45.3 45.6 0.94 0.955

(g dayÿ1) 944 878 918 941 33.1 0.262

a Statistical signi®cance of treatment effects by F-test.

J Sci Food Agric 79:1441±1447 (1999) 1445

Synchrony of energy and N release in synthesis of microbial protein in cows

a substantial excess of Effective Rumen Degraded

Protein (ERDP)11 relative to the supply of Fermen-

table Metabolizable Energy (FME)11 in order to

ensure a potential response of MPS to the intraruminal

addition of maltodextrin. Calculation of the ERDP to

FME ratio for the basal diet, using the factors in

AFRC11 yields a value of 14.1g ERDP MJÿ1 FME for

the BASAL treatment and 12.1g ERDP MJÿ1 FME

for the treatments in which maltodextrin was infused

into the rumen. The value for BASAL is well in excess

of the requirement of 11g ERDP MJÿ1 FME (AFRC

1992) and even for the infusion treatments the value is

about 10% over requirement.

Maltodextrin was chosen as the water-soluble

substrate to be infused in preference to the sucrose

used by Kim et al3 because it is considered more

relevant to practical diets where the main source of

readily fermentable carbohydrate is usually starch.

The intention was that the maltodextrins would

represent normal intermediates in the ruminal degra-

dation of starch. The arrangement of feeding times

and infusion patterns was as used by Kim et al.3

The present results show that, in contrast to those

reported by Kim et al,3 altering the degree of syn-

chrony markedly in¯uenced MPS to such an extent

that when the maltodextrin was infused asynchro-

nously, MPS was not increased above the BASAL

level. The incremental increase of MPS in response to

the infusion of 2kg maltodextrin on the CONT and

SYNC treatments, at about 6.5g microbial crude

protein kgÿ1 FME, was only about 60% of the

expected response.11 The reasons for the low response

are not clear.

Lactic fermentation of starch and sugars can result

in markedly reduced yields of ATP to rumen

bacteria.12 However, lactic acid appeared to be only

a minor product of the fermentation. Indeed, the

pattern of change of ruminal concentrations of lactic

acid during the interval between meals indicated that

the main source of lactic acid was the silage itself

because the same pattern was seen for all treatments

with a maximum at 1h after feeding. Even when

maltodextrin would be expected to be the main

substrate being fermented, at 8.5h after feeding with

the ASYNC treatment, the concentration was still very

low, at 1.5mmol litreÿ1.

Although the calculations above show a substantial

overall excess of ERDP, this does not rule out the

possibility that ruminal concentrations of ammonia

might have been suboptimal for MPS at times during

the feeding cycle. The minimum concentration

needed to support maximum rates of MPS is not

known but the earlier suggestion of 50mg ammonia-N

litreÿ1 13 has been challenged in later publications.14,15

If we take the value of about 100mg ammonia-N

litreÿ1 suggested by Balcells et al,15 then ammonia

concentrations could have been limiting MPS for 3±

4h of the interval between meals for all the infusion

treatments (Fig 1).

Also to be considered is the possibility of a shortage

of preformed amino acids and peptides in the rumen at

times during the feeding cycle.16 Although the basal

diet contained a high level of supplementary protein as

groundnut meal, the 12-h interval between meals may

have led to de®cient supplies of peptides and amino

acids in the later phases of the feeding cycle.

Furthermore, it has been argued that amylolytic

bacteria, which would be expected to be present in

large numbers on the maltodextrin treatments, need

greater amounts of amino acids and peptides for

maximum growth rates than do their cellulolytic

counterparts.17

It should also be remembered that the infusion of

maltodextrin, as readily fermentable carbohydrate,

might have reduced the ruminal digestion of ®bre on

the basal diet18,19 which would mean that the total

yield of FME on the infusion treatments was less than

assumed in the calculations above. It is dif®cult to

estimate the likely magnitude of effects on the ruminal

digestion of ®bre. However, it is worth noting that, for

all the infusion treatments, ruminal pH was depressed

below the suggested threshold value of 6.1 for

cellulolysis18 for 4±6h of the 12-h interval between

meals. The effect was most marked for the ASYNC

treatment, for which the ruminal pH was less than 5.9

for 4h of the 12-h period.

The effects of synchrony on MPS are consistent

with the hypothesis that the bacteria were unable to

convert maltodextrin to storage polysaccharide when it

was infused asynchronously with the ruminal release of

ammonia. Presumably, the maltodextrins were fer-

mented but the ATP released could not be used to

support MPS on the ASYNC treatment (see Ref 6).

The reduction of the concentration of urea in the

blood with all the infusion treatments relative to

BASAL can be explained by the effective reduction

in the CP content of the diet from 196 to 173g kgÿ1

DM by infusion of 2kg dayÿ1 of maltodextrin.20 The

ASYNC treatment was as effective as the other two

infusion treatments in reducing the blood concentra-

tion of urea and the urinary excretion of nitrogen,

showing that the ef®ciency of capture of nitrogen in the

rumen had little in¯uence on the overall ef®ciency of

nitrogen use. This is not surprising because the

calculated supply of amino acids was about 20% over

requirement11 and hence virtually all the extra amino

acids from the increased yield of microbial protein

would be expected to be deaminated. Some support

for this view comes from the milk production results

(see below) which indicate that protein output in milk

was probably not related to the output of microbial

protein from the rumen, because the highest yield of

milk protein was obtained with the ASYNC treatment,

for which MPS was not increased above that for

BASAL.

The experiment was not designed to examine effects

on milk production, in that the experimental periods

were too short to obtain reliable estimates of effects of

changes in ruminal digestion on milk yield and

composition (see Ref 21). For completeness, the milk

1446 J Sci Food Agric 79:1441±1447 (1999)

KH Kim, J-J Choung, DG Chamberlain

production results are presented and will be discussed

brie¯y below, but it is recognized that no ®rm

conclusions can be drawn; they may, at best, serve as

a pointer for future investigations.

Effects of the treatments on milk production were

seen in the yield and concentration of protein and fat.

The effects on milk fat, particularly the lower

concentration for CONT than for SYNC, are not

easy to explain in the absence of differences in ruminal

fermentation pattern. The increased (P<0.05) con-

centration of milk protein with all the infusion

treatments compared with BASAL is probably due to

the well-established effect of an increased intake of

ME on milk protein content22 but the higher

(P<0.05) yield of milk protein for ASYNC over the

CONT treatment is dif®cult to explain. As mentioned

above, the reliability of the milk production results is

uncertain but they clearly highlight the need for further

research, especially since the infusion treatments had

different effects on some blood metabolites and

insulin.

In conclusion, these results, considered together

with results published previously, suggest that the

degree of synchrony in the ruminal release of energy

and nitrogen is likely to in¯uence MPS only with

certain diets such as those containing high concentra-

tions of readily fermentable carbohydrate. These

®ndings are consistent with the view that ruminal

bacteria have limited capacity to store intracellular

polysaccharide which, in turn, limits their ability to

buffer the effects of severe mismatching of energy and

nitrogen release. The challenge now is to de®ne the

critical level of readily fermentable carbohydrate in the

diet beyond which ruminal synchrony in¯uences

MPS.

ACKNOWLEDGEMENTSWe thank Mrs I Stewart, Mr J Davidson and Miss M

McLelland for skilled technical assistance and Mr JR

Munro and his staff for the care of the animals during

the experiment. This research was funded by The

Scottish Of®ce Agriculture, Environment and Fish-

eries Department and the Rural Development Admin-

istration of Korea.

REFERENCES1 Chamberlain DG and Choung J-J, The importance of rate of

ruminal fermentation of energy sources in diets for dairy cows,

in Recent Advances in Animal Nutrition ±1995, ed Garnsworthy

PC and Cole DJA, Nottingham University Press, Nottingham,

UK. pp 3±27 (1995).

2 Beever DE and Cottrill BR, Protein systems for feeding ruminant

livestock: European assessment. J Dairy Sci 77:2031±2043

(1994).

3 Kim KH, Oh Y-G, Choung J-J and Chamberlain DG, Effects of

varying degrees of synchrony of energy and nitrogen release in

the rumen on the synthesis of microbial protein in cattle

consuming grass silage. J Sci Food Agric 79:833±838 (1999).

4 Cheng KJ, Hironaka R and Roberts DWA, Cytoplasmic

glycogen inclusions in cells of anaerobic Gram-negative rumen

bacteria. Can J Microbiol 19:1501±1506 (1973).

5 van Kessel JS and Russell JB, The endogenous polysaccharide

utilization rate of mixed ruminal bacteria and the effect of

energy starvation on ruminal fermentation rates. J Dairy Sci

80:2442±2448 (1997).

6 Russell JB, Strategies that ruminal bacteria use to handle excess

carbohydrate. J Anim Sci 76:1955±1963 (1998).

7 ARC, The Nutrient Requirements of Ruminant Livestock. Agricul-

tural Research Council, Commonwealth Agricultural Bureaux,

Farnham Royal, Slough, Berkshire, UK (1980).

8 Chamberlain DG, Robertson S and Choung J-J, Sugars versus

starch as supplements to grass silage: effects on ruminal

fermentation and the supply of microbial protein to the small

intestine, estimated from the urinary excretion of purine

derivatives, in sheep. J Sci Food Agric 63:189±194 (1993).

9 Chamberlain DG, Choung J-J and Robertson S, Protein

nutrition of dairy cows receiving grass silage diets: effects of

feeding a protein supplement of unbalanced amino acid

composition. J Sci Food Agric 60:425±430 (1992).

10 Lawes Agricultural Trust, Genstat 5, Rothamsted Experimental

Station, Harpenden, Hertfordshire UK (1990).

11 AFRC, Technical Committee on Responses to Nutrients, Report No.

9, Agricultural and Food Research Council, Commonwealth

Agricultural Bureaux, Wallingford, Oxfordshire, UK (1992).

12 Strobel HJ and Russell JB, Effect of pH and energy spilling on

bacterial protein synthesis by carbohydrate-limited cultures of

mixed rumen bacteria. J Dairy Sci 69:2941±2946 (1986).

13 Satter LD and Slyter LL, Effect of ammonia concentration on

rumen microbial protein production in vitro. Br J Nutr 32:199±

208 (1974).

14 Kang-Meznarich JH and Broderick GA, Effects of incremental

urea supplementation on ruminal ammonia concentrations

and bacterial protein formation. J Anim Sci 51:422±431

(1981).

15 Balcells J, Guada JA, Castrillo C and Gasa DJ, Rumen digestion

and urinary excretion of purine derivatives in response to urea

supplementation of sodium hydroxide-treated straw fed to

sheep. Br J Nutr 69:721±732 (1993).

16 Hespell RB and Bryant MP, Ef®ciency of rumen microbial

growth: in¯uence of some theoretical and experimental factors

on YATP. J Anim Sci 49:1640±1659 (1979).

17 Russell JB, O'Connor JD, Fox DG, van Soest PJ and Sniffen CJ,

A net carbohydrate and protein system for evaluating cattle

diets. J Anim Sci 70:3551±3561 (1992).

18 Mould FL, Orskov ER and Mann SO, Associative effects of

mixed feeds. 1. Effects of type and level of supplementation

and the in¯uence of the ruminal pH on cellulolysis in vivo and

dry matter digestion of various roughages. Anim Feed Sci

Technol 10:15±30 (1983).

19 Khalili H and Huhtanen P, Sucrose supplements in cattle given a

grass silage-based diet. 2. Digestion of cell wall carbohydrates.

Anim Feed Sci Technol 33:263±273 (1991).

20 Oltner R and Wiktorsson H, Urea concentrations in milk and

blood as in¯uenced by feeding varying amounts of protein and

energy to dairy cows. Livestook Prod Sci 10:457±467 (1983).

21 Rook JAF and Thomas PC, Nutritional Physiology of Farm

Animals, Longmans, London, UK, p 573 (1983).

22 Coulon JB and Remond B, Variations in milk output and milk

protein-content in response to level of energy supply to the

dairy cow: a review. Livestock Prod Sci 29:31±47 (1991).

23 Susmel P, Stefanon B, Plazzotta E, Sphanghero M and Mills CF,

The effect of energy and protein intake on the excretion of

purine derivatives. J Agric Sci (Camb) 123:257±265 (1994).

J Sci Food Agric 79:1441±1447 (1999) 1447

Synchrony of energy and N release in synthesis of microbial protein in cows