Classification of Feedstuffs

Classification of Feedstuffs

A feedstuff may be defined as any component of a ration that serves some useful function. Most feedstuffs provide a source of one or more nutrients, but ingredients may also be included to provide bulk, reduce oxidation of readily oxidized nutrients, to emulsify fats, provide flavor, color, or other factors related to acceptability, rather than serving strictly as a source of nutrients. Generally speaking, medicinal compounds are usually excluded. The usual classification of feedstuffs, essentially as given by NRC (30) but with a number of added items, is as follows:Roughages

Pasture, range plants, and plants fed green

Grazing plants

Growing

Dormant

Soilage or green crop

Cannery and food crop residues

Dry forages and roughages

Hay

Legume

Nonlegume

Straw

Fodder

Other products with > 18% crude fiber

Corn cobs

Hulls

Shells

Sugar-cane bagasse

Paper and wood

Silages

Corn

Sorghum

Grass

Legume

Miscellaneous

Concentrates

Energy feeds

Cereal grains

Milling by-products (primarily from cereal grains)

Molasses

Seed and mill screenings

Animal and vegetable fats

Miscellaneous

Brewery by-products

Waste from food processing plants

Garbage, manures, and sewage

Roots and tubers

Fruits and nuts

Protein concentrates Animal

Marine

Avian

Seeds from plants

Dehydrated legumes

Single-cell sources (bacteria, yeast, algae)

Nonprotein nitrogen (urea, etc.)

Mineral supplements

Vitamin supplements

Nonnutritive additives

Antibiotics

Antioxidants

Buffers

Colors & flavors

Emulsifying agents

Enzymes

Hormones

Medicines

Roughages

Roughages are the natural feeds for all herbivorous animals existing under natural conditions and such food provides the major portion of their diet for most if not all of the year. Harvested and stored roughages (hays, silages and other forms) are utilized by man to increase animal productivity under conditions that would not allow it otherwise in nature. Thus, roughages are of primary interest for domestic ruminants, horses, and other herbivores. Although other species such as swine can survive on roughage, productivity with no other source of feed would be too low to be economical in our current economy.Nature of Roughages

To most livestock feeders, a roughage is a bulky feed that has a low weight/unit of volume. This is probably the best means of classifying a feedstuff as a roughage, but any means of classifying roughages has its limitations since, due to the nature of the products we are dealing with, there is a great variability in physical and chemical composition. Most feedstuffs classed as roughages have a high crude fiber (CF) content and a low digestibility of nutrients such as crude protein and energy. If we attempt, as does NRC (30), to classify all feedstuffs as roughages that have >18% CF and/or with low digestibility, we immediately find exceptions. Corn silage is a good example; it nearly always has >18% CF, but the TDN content of well-eared corn silage is about 70% on a dry basis. Lush young grass is another example. Although its weight/unit volume may be relatively low and fiber content relatively high, its digestibility is quite high. Soybean hulls are another exception for ruminants.

Most roughages have a high content of cell-wall material (see Ch.2). The cell-wall fraction may have a highly variable composition, but contains appreciable amounts of lignin, cellulose, and other components. In contrast, roughages are generally low in readily available carbohydrates as compared to cereal grains.

The amount of lignin is a critical factor with respect to digestibility. Lignin is an amorphous material which is closely associated with the fibrous carbohydrates of the cell wall of plant tissue. It greatly limits fiber digestibility, probably because of the physical barrier between digestive enzymes and the carbohydrate in question. Removal of lignin with chemical methods greatly increases digestibility by rumen microorganisms and, probably, by cecal organisms. Lignin content of plant tissue gradually increases with maturity of the plant and a high negative correlation exists between lignin content and digestibility, particularly for grasses, although somewhat less for legumes (see Ch.2 of Church et al, 8). There is also evidence that the silica content of plant tissue is negatively related to fiber digestibility.

The protein, mineral and vitamin contents of roughages are highly variable. Legumes may have 20% or more crude protein content, although a third or more may be in the form of nonprotein N. Other roughages, such as straw, may have only 3-4% crude protein. Most others fall between these two extremes.

Mineral content may be exceedingly variable; most roughages are relatively good sources of Ca and Mg, particularly legumes. P content is apt to be moderate to low, and K content high; the trace minerals vary greatly depending on plant species, soil, and fertilization practices.

In overall nutritional terms roughages may range from very good nutrient sources (lush young grass, legumes, high-quality silage) to very poor feeds (straws, hulls, some browse). The nutritional value of the very poor can often be improved considerably by proper supplementation or by some feed preparatory methods. The feeder must, however, use some, wisdom in selecting the appropriate roughage for a given class and species of animal.

Factors Affecting Roughage Composition

A number of factors may affect roughage composition and nutritive value, if we ignore the generally poor-quality roughages. Maturity at harvest (or grazing) has one of the more pronounced effects. One relatively detailed example of stage of maturity on composition and digestibility of orchard grass [Dactylis glomerata] is shown in Table 18-1. Many other examples are available in the literature. In Table 18-1 and Fig. 18-1, note the rapid decline in crude protein, particularly. A gradual decline occurs also in ash and soluble carbohydrates and an increase in lignin, cellulose and CF, all during a 6 wk period. Digestibility declines, also, as these changes occur in plant composition. The changes that occur will depend on the plant species and on the environment in which the plant is grown. For example, if the growing season progresses rather rapidly from cool spring weather to hot summer weather, changes in plant composition will be more rapid than where the weather remains cool during plant maturation, especially in a cool season grass. In plants such as alfalfa [Medicago sativa], which has quite different growing habits than grass, rapid changes take place as the plant matures and blooms. Crude portein contents given by NRC publications indicate the following values (% on dry basis) for second cuttings: immature, 21.5; prebloom, 19.4; early bloom, 18.4; mid-bloom, 17.1; full bloom, 15.9; and mature, 13.6. Corresponding changes in TDN range from 63 to 55%. Part of these differences are due to the

Table 18-1. Effect of maturity on composition and digestibility of orchard grass._______________________________________________Item

Stage of Maturity

____________________________________________

6-7 high 8-10high 10-12high 12-14highComposition,% cut 5/19 cut 5/31 cut 6/14 cut 6/27

pasture late pasture early hay mature hay_________________________________________________________________Composition, %

Crude protein 24.8 15.8 13.0 12.4 Ash 9.3 6.8 7.1 7.2

Ether extract 4.0 3.5 3.9 4.2

Organic acids 6.3 6.0 5.4 5.0

Total carbohydrates* 49.9 63.0 64.4 63.1 Sugars 2.1 9.5 5.4 2.4

Starch 1.2 9.5 0.8 0.9

Alpha cellulose 19.5 19.8 19.1 27.7

Beta & gamma cellulose 3.4 5.4 3.8 2.5 Pentosans 15.1 15.8 16.8 18.1

Nitrogen-free-extract 35.0 45.7 44.2 41.2

Lignin 5.7 5.0 6.2 8.1 Crude fiber 26.9 28.2 31.8 35.0

Digestibility, % Dry matter 73 74 69 66

Crude protein 67 63 59 59

Crude fiber 81 77 71 68

______________________________________________________

From Ely et al (12)

* Total carbohydrates = (crude fiber + organic acids)

fact that the plant loses leaves as it matures, and leaves have higher nutrient value than the remainder of the plant. As plants mature, there is also a decline in concentration of Ca, K, and P and for most of the various trace minerals (33).

For many years, soil fertility and fertilization practices have been known to have a pronounced effect on quality of forage and crops produced. In addition, some alterations in plant composition may occur as a result of these factors, although the differences are much less dramatic than those changes associated with increased maturity, and results given in the literature show many discrepancies in responses to fertilizer. In pastures with mixed plant species, one obvious change that may occur as a result of fertilization is an alternation in the4 vegetative composition as some plants respond more to fertilizer than others. If a grass-legume mixture is fertilized with high levels of N, for instance, this practice is apt to kill out the legume or to stimulate the grass much more than the legume. Fertilization of grasses with N tends to increase total, nonprotein, and nitrate N of the plants. Nitrate levels usually drop off rapidly after fertilization, however. K content and, perhaps, some other minerals may increase in response to N; however, the marked increase in plant growth that may be obtained by high levels of N may be expected to result in some dilution of most mineral elements, particularly during the first few days or weeks or rapid growth after fertilization (33).

Digestible protein is apt to be increased and, in some instances, palatability and dry matter intake may increase in response to fertilization with N, although not all data agree on some of these points. Fertilization studies have shown, in general, that plant concentration of most of the mineral elements may be increased by fertilization with the element in question. P use may increase palatability when used alone or in combination with N. Thus, results to date indicate that soil fertility and/or fertilization practices may alter nutrient concentration and consumption of forage plants.

Harvesting and storage methods may have some effect on nutritive value of roughages, particularly when forage cut for hay is unduly bleached by the sun or damaged by dew and/or rain. Sun bleaching results in a rapid loss of synthetic vitamin A. Leaching by rain will result in losses in soluble carbohydrates and N, and added handling required may result in loss of leaves. Any harvesting method used for legumes that tends to reduce leaf loss will affect nutritive value. With respect to storage, hays may lose a considerable amount of original nutritive value if stored too wet with resultant heating and mold formation. Otherwise, there is relatively little nutritive loss if the hay is stored in dry conditions over a period of several years. The same comment applies to silages, as well-preserved silages will keep for a number of years without much effect on nutritive value.

Latitude, along with accompanying effects of temperature and light intensity, may have an appreciable effect on plant composition and nutritive value. Not a great deal of information is available on this subject, but data do indicate that nutritive value of forage cut on a given date is apt to be higher as we go away from the equator toward the poles (northern or southern).

Pasture and Grazed Forages

A wide variety of vegetation is utilized by herbivorous animals. With respect to agricultural production, herbage is usually divided into native and cultivated species, the latter being utilized to improve productivity or versatility of crop production. Herbage may also be divided into the following classes:Grasses members of the family

Gramineae (5000 + species)

Cool season grasses grasses that make their best growth

Warm season grasses grasses that grow slowly in the early spring and grow most actively in early summer or fallLegumes members of the family Leguminosae(11000+species)

Forbs primarily broadleaf nonwoody, plants

Browse- woody plants consumed in some degree by ruminants, particulary selective eaters such as deer and antelope

Grasses

Grasses are by far the most important plant that man is concerned with agriculturally, because the grass family not only includes all of the wild and cultivated species used for grazing but also the cultivated cereal grains and sorghum species. In this, however, will be concerned only with grass as a forage, and will not consider it from an agronomic point of view. The discussion will also be very general because of the tremendous numbers of grasses of importance.

As a food for grazing animals, grass has many advantages. Most grass species are quite palatable when immature and only a few are highly toxic for any appreciable part of the grazing season. Grasses of one type or another have the ability to grow in most environments in which ruminants can survive, arctic regions being one notable exception. Furthermore, nutrients supplied in grasses roughly provide needed amounts that more or less parallel animal needs during a yearly life cycle of reproduction and production, except during midwinter in cold climates.

Some more or less typical values for chemical composition are illustrated in Table 18-1. Early in the growing season, grasses- especially cool season species- have a very high water content and an excess of protein for ruminants animals. The result is that animals may have diarrhea and, because of the low dry matter content may have difficulty in obtaining a maximum intake of energy. Grass proteins are usually high in the amino acid, agrinine, and also contain appreciable amounts of Glutamic acid and lysine. If N application is liberal, and particularly if S is deficient there is apt to be a high level of NPN in the form of amino acids and amides and a relative deficiency of the S-containg amino acids. High nitrate may also result from fertilization. Toxic symptoms may occur at levels of about 0.07% nitrate N in dry matter and amounts on the order of 0.22% may be fatal to ruminants; how-ever if ruminants are adapted and fed on high nitrate grasses continuously, toxicity is less likely as rumen microorganisms are capable of reducing nitrate to ammonia which is well utilized.

In comparison with legumes such as alfalfa, the protein content of grasses is nearly always lower, particularly in mature plants. Digestible energy is very good in young grass, but declines rapidly with maturity. Mature plants, especially those that are weather leached, will be low in digestible energy and protein, as well as in other solubles such as carbohydrates and some of the mineral and in carotenes; thus, this type of plant material may not meet the animals needs, even when productive requirements are quite low.

Mineral content of grasses may vary considerably depending on species and soil fertility, particularly. Of those elements of concern to ruminants, grasses are usually adequate in Ca, Mg, and K, but are apt to be borderline or deficient in P. Trace minerals also vary considerably; recent evidence from Canada (26) indicates that 80% or more of forage species measured contained less than levels generally considered adequate for ruminants. Ranges and typical values to be expected are shown in Table 18-2.

The desirability of different grasses depends on the local environment and their growing habits and on animal needs. Considerable differences may exist in the composition of grasses that fall into the cool-or warm-season classes. Generally cool-season grasses mature at slower rates and their quality deteriorates less rapidly than do warm-season grasses. Lush, young grass is usually quite palatable, but palatability usually declines as the plants mature, and most animals object to the seed heads of many grass species. Quality differences between species of grasses become more evident with maturity. Furthermore, regrowth of grass in the fall is usually not as nutritious as spring grass, partly due to the Table 18-2. Range and typical mineral concentrations for pasture grasses and alfalfa plants.

Mineral

ElementGrasses Alfalfa

Low Typical High Low Typical High

Major elements, % dry matter

Ca 1.0 2.5

Mg 0.3 0.6

K 3.0 3.0P 0.4 0.7S 0.3 0.7Trace elements, ppm of dry matter

Fe 200 300

Co 0.30 0.3

Cu 10 15Mn 250 100Mo 5 5Se 5 5Zn 100 50

lower concentration of soluble carbohydrates. Cultivated grasses held in high esteem include perennial ryegrass [ Lotium perenne ], Italian ryegrass [ lotium multiforum ], orchard grass [Dactylis glomerata], blue grass [Poa spp], and smooth brome grass [Bromus inermus]. Others considered less desirable include Bermuda grass [Cynodon dactylon], foxtail [Alopecurus pratensis], bent [Agrostis spp] and tall fescue [Fescuta arundinacea].In addition to varying in growth habits, these species may vary in nutrient composition,palatability, and digestibility.

In many regions some of the cereals are used for pasture particularly winter wheat, with lesser use of barley, oats, and rye. These plants can be pastured during the winter and early spring with little or no effect on grain yield, provided soil conditions permit. The forage of these plants is quite high in readily available carbohydrates (50%+) and crude protein is high. Extensive use of such pasture is made in the southwestern states of the USA, particularly for growing calves and lambs.

Several sorghum species are also used for pasture or harvested forage. Sudan grass [Sorghum vulgare sudanense] is one of the more common ones used in the USA, but others, such as Johnson grass [Sorghum halapense] find some use. Sudan-sorghum hybrids have also been developed. These species are often utilized because they can be sown during early summer in temperate areas and will produce late summer and fall pastures. They are prone to have high levels of glycosides which can be converted to prussic acid (hydrocyanic acid), particularly following drought or frost damage, so care must be used if these conditions occur while pasture is in use.Legumes

A wide variety of legumes are utilized by grazing animals, although the cultivated legumes comprise a much smaller group than do cultivated grasses. In overall usage, alfalfa [Medicago sativa] is by far the most common legume used for pasture, hay-crop silage, and hay in most temperate climates. As a point of reference, alfalfa is known a s Lucerne in most English-speaking areas other than in North America.

Other legumes that find extensive usage for pasture or hay include clovers such as ladino or red [Trifolium pretense], white [T.repens] and subterranean [T.subterraneum], as well as common lespedeza [Lespedeza striata], lupines [Lupinus spp] and vetches [Vicia spp].

Legumes have higher protein contents than grasses, particularly in more mature plants. Fiber in the stems tends to be particularly high and soluble carbohydrates relatively low. The leaves are rich sources of nutrients but stems are of much less value, especially in mature plants. Changes in plant composition with maturity are largely from lignification and increased fiber in the stems and to reduced leaf:stem ratio. Compared to grasses, legumes have characteristically high concentrations of Ca, Mg, and S (Table 18-2) and, frequently, Cu. They tend to be lower in Mn and Zn than grasses. On the whole, legumes are palatable, although most are bitter and may require some adaptation before they are readily consumed by cattle.Some legumes, particularly alfalfa and white, ladino, and red clover are prone to cause bloat in grazing ruminants, especially cattle. Bloat is caused primarily by foam-producing compounds from plant, of which cytoplasmic proteins and, perhaps, pectins are the most important. Foam in the rumen causes entrapment of normal rumen gases which cannot be gotten rid of, resulting in a gradual increase in rumen pressure and, if not relieved, eventual suffocation of the animal. Recent evidence indicates that alfalfa plants probably can be selected to have a lower content of the proteins that are involved in bloat production.Native Pastures and Range

Pastures and rangeland comprised of uncultivated native forage plants account for many millions of acres of land in areas of the world where the environment, soil, or topography rule out intensive agricultural methods. These areas are apt to contain a wide range of grasses, sedges, forbs, and browse. The nutrient properties of these various plants vary widely and, in addition, there apt to be distinct seasonal patterns of use different grazing animals.

Miscellaneous Forage Plants

In some areas and for some specific seasonal usage, plants such as the cabbage family [Brassica spp] are used extensively. Kale, cabbage, and rape are included in this group. Rape for example is often planted for use as fall pasture by sheep. The tops of root crops such as beets and turnips, are also frequently used as forage. As a part of the total resource, however, these crops account for a very small percentage of the total.Harvested Dry Roughages

Roughages stored in the dried form are the most common type used for feeding during the time of the year when grazing is not available or for feeding of confined animals. Roughages harvested in the form of long hay or bales require a relatively high labor input and present difficulties in mechanical handling, both during harvest and feeding, with the result that the cost of nutrients is increased as compared to cereal grains in intensive livestock operations. Fortunately, machinery currently available allows rather complete mechanization in operations where it is financially feasible, and continual improvement is being made in this respect.

Hay Hay from grasses or legumes is one crop that is grown and harvested almost exclusively for animal usage. Haymaking has been practiced for many centuries and much information has been accumulated on the nutritive value of hays as affected by many different factors too numerous to discuss in detail here. Although haymaking is the most common method of conserving green crops, its relative importance has declined some in recent years with the development of newer methods of forage preservation.

The intent in haymaking is to harvest the crop at a more or less optimum stage of maturity which will provide a maximal yield of nutrients/ unit of land without damage to the next crop. To make good hay, the water content of the plant material must be reduced to a point low enough to allow storage without marked nutritional changes. Moisture content of green herbage may range from 65 to 85% or more, depending on maturity and the plant species. For hay to keep satisfactorily in storage, the water content must be reduced to about 15% or less.

Losses in Haymaking

It is impossible to cut, dry and move hay into storage without losses occurring in the process, although it may be possible to harvest more units of nutrients/unit of land than could be obtained by grazing due to trampling and feed refusal resulting from contamination by dung and urine and to selective grazing of some species of plants. Both the quality and quantity of field-cured hay that can be harvested depends on such factors as maturity when cut, method of handling, moisture content, and weather conditions during harvest; for example, rain on freshly cut hay will cause little damage; however, when hay is partially dried, rain is very damaging. Early cut hay in many areas is often of low quality because of rain and resultant spoilage, leaching, and leaf loss. One report indicates dry matter losses ranging from about 6% for artificially dehydrated hay up to about 33% for rain-damaged field-cured hay. Another report indicated the following losses: plant respiration losses (before plant is dry), 3.5% in 24 hr; leaching by rain, 5-14%; and leaf shattering in legume hays, 3-35%. Thus, very substantial amounts of dry matter may be lost in haymaking under adverse conditions; an average loss of 15-20% is not abnormal for legume hays.

Changes During drying

Ample evidence shows that rapid drying, provided it is not accompanied by excessively hot temperatures, results in the least changes in chemical components of forage. Machines such as crimpers have been developed to crush the stems of plants like alfalfa and speed up the drying process. If drying is slow in the field, stack, or bale, appreciable changes may occur as a result of plant enzymes, microorganisms, or oxidation. After the plant is cut, the cells continue to function for a time with the result that soluble carbohydrates may be oxidized. Oxidative reactions may continue for some time, depending on the temperature and how the hay is stored. The most obvious change is a loss in pigmentation as plants lose carotenes by oxidation. Proteins may also be modified as some hydrolysis occurs, resulting in relatively greater amounts of NPN, primarily amino acids.Table 18-3. Composition and digestibility of green ryegrass and material from same field which was dried artificially or made into wilted or unwilted silage. aItem Fresh Dried wilted Unwilted

Grass grass silage silage

Composition

of dry matter

Organic matter% 90.8 92.0 92.2 91.7

Total water-soluble 9.2 8.4 trace trace

Carbohydrate, %

Cellulose, % 24.2 24.3 25.0 26.8

Hemicellulose, % 14.0 13.3 12.9 13.1

Total N, % 2.85 2.99 3.09 3.08

Gross energy, Kcal/g 4.59 4.55 4.46 4.89

Digestibility, %

Energy 67.4 68.1 67.5 72.0

Cellulose 75.2 75.5 76.5 80.6

Hemicellulose 59.4 57.7 59.9 63.2 N 75.2 71.0 76.5 76.4

Slow drying is almost always accompanied by excessive mold growth which reduces the palatability and nutritive value of hay.

Hay stored in the stack or bale while too wet to dry rapidly may undergo enough fermentation to result in marked temperature increases, which may cause browning and, sometimes, spontaneous combustion. Newly baled alfalfa hay should have no more than 35% moisture to avoid these problems. Excess heating (25) or molding results in a marked reduction in digestibility of protein and energy.

If drying is not complicated by weather factors, relatively little change in the composition takes place between green plant and hay (5.14) nor is there any pronounced effect on nutrient utilization (see Table 18-3).Animals generally ingest dry matter from fresh herbage at a slower rate than for hay, and some slight differences may occur in rumen fermentation, digestibility, and site of digestion in ruminants, but the differences appear to be inconsequential.

Thus, we see that drying may not have any great effect on forage utilization. In practice, however, we must expect some loss of leaves in legumes and reduced soluble carbohydrates. Hay, if made from moderately mature plants, will have lower protein and digestible energy than young herbage, but is apt to be better than very mature herbage. Nutritive properties of hays, are, then, similar to those of forages, but with slightly to greatly reduced values depending on freedom from weather damage and method of harvesting.

Artificially Dried forage

Rapid drying is required for good haymaking. At one time in the USA, particularly in areas where weather was a problem, considerable interest was shown in barn drying. This is accomplished by circulating air through the hay after storage. Although a very good product can be produced, interest has declined with greater usage of silage and recent developments in bale-handling machinery.

Dehydration of herbage with appropriate machinery is a viable industry both in the USA and some areas of northern Europe. In the USA, alfalfa is the primary crop that is dehydrated, but in Europe, grasses or grass clover mixtures are more commonly used. In making dehydrated alfalfa, the herbage is cut at a prebloom stage, dried quickly at hot temperatures ground, and sometimes pelleted. Because carotene pigments are important, the product is often stored using inert gases such as N2 to reduce oxidation. Herbage so processed is high in crude protein and quite digestible, moderately low in fiber, and has high carotene content. The relatively low fiber content makes such feedstuffs more suitable for monogastric species such as poultry and swine and, in the USA, a high proportion of dehydrated alfalfa goes into commercial rations for these species. For poultry, the carotenes and xanthophylls serve to increase pigmentation of the skin of broilers or the volk of eggs as well as provide protein and other nutrients. For swine, particularly sows, nutrients of interest are the vitamins, Ca and trace minerals. These feeds serve very well for horses or ruminants, but generally are more expensive/unit of nutrients provided as compared to other roughage sources.

Straws and Chaff An appreciable amount of straw and chaff is available for animal feed in most farming areas, although much less than in the days when stationary threshing machines were used for harvesting cereal grains. Straw consists mainly of the stems and variable amounts of leaves of plants that remain after the removal of the seeds. Chaff consists of the small particles removed from the seed head along with limited amounts of small or broken grains. The primary supply of straw and chaff comes from the small cereal grains wheat, barley, rye, rice, oats but, in some areas, substantial amounts may be available from the grass or legume seed industry and from various miscellaneous crops. As a whole, straws are very low in digestible protein, very high in fiber and, usually, lignin, and are poor feed, although some are4 of less value than others. For example, values given from NRC (30) for winter wheat straw (dry basis) are: crude protein, 3.2%; crude fiber, 40.4%; and digestible energy (cattle), 1.92 Mcal/kg or 47% TDN. Of the various cereal straws, that from oats is regarded as the best, partly because the grain is often harvested before it is fully ripe. As a feedstuff, straws are best used as a diluent in high concentrate rations or as the basal feed for wintering cattle when properly supplemented with deficient nutrients protein, vitamin A, minerals. Even though straws are low in metabolizable energy, the energy derived from that which is digested and from the heat increment provides energy that can be used for animals, such as pregnant cows, which have a low productive requirement.

Miscellaneous

In the USA nearly all of the grain from corn and sorghum is now field harvested and often the cobs or threshed seed head are left in the field, along with a substantial amount of grain at times. The nutritive problems here are the same as with straws, and some supplementary feeding is nearly always required to supply needed minerals, carotene, and protein. Protein may be less critical than with straws.

Harvested High Moisture Roughages Green Chop [Soilage]

Green chop (or soilage) is herbage that has been cut and chopped in the field and then fed to livestock in confinement. Plants used in this manner include the forage grasses, legumes, sudan grass, the corn plant and, at times, residues of food crops used for human consumption.

Although this is one of the simplest means of harvesting herbage, it requires constant attention to animal needs as opposed to other methods of harvesting herbage. A major advantage of use of green chop is that more usable nutrients can be salvaged/unit of land than with other methods such as pasturing, haymaking, or ensiling. Thus, it is often feasible to harvest in this manner rather than using such crops in other ways, provided land productivity is relatively high. When herbage growth outruns daily need, the excess can be made into hay or silage before it becomes too manure for efficient usage. Weather, of course, is less of a factor than in haymaking.

Data, in general, indicate that beef cattle will gain as well as when pastured using intensive systems such as short term rotations or strip grazing and that dairy cows do equally well when fed soilage as when fed alfalfa preserved in other ways. Because harvestable nutrients can be increased, the result in recent years has been a steady increase in use of green chop, particularly for lactating cows. Practical experience has indicated that optimal usage is obtained when green chop is fed along with hay or silage rather than by itself, partly because total intake tends to be greater.

Silage

Silage has been used for feeding animals, primarily ruminants, for many years. It is the material produced by controlled fermentation of high moisture herbage. When such material is stored under anaerobic conditions (in the absence of oxygen) and, if the supply of fermentable carbohydrates is adequate, sufficient lactic acid is produced to stabilize the mass so that no more fermentation occurs. If undisturbed, silage will keep for an indefinite period. Alternate methods, primarily used in Europe, require the addition of strong acids which lower the pH, thus preventing fermentation.

Good silage is a very palatable product which is well utilized (see Table 18-4), and excellent results may be obtained with high-producing animals such as lactating cows. In addition to any advantages in harvesting or in nutritive properties, the fermentation that occurs usually will greatly reduce the nitrate content, if nitrate is present, and other toxic materials, such as prussic acid, will be reduced in amount.

Most silage in the USA is made from the whole corn plant [Zea mays] or from any of a number of sorghum varieties in areas