also called animal feed, foodstuff grown or developed for livestock and poultry, selected and prepared to provide highly nutritional diets that both maintain the health of the animals and increase the quality of such end products as meat, milk, or eggs. Many of the feeds produced today are the result of research, experimentation, and chemical analysis and are the subject of continuing study by agricultural scientists. Animals in general require the same nutrients as humans. Some feeds, such as pasture grasses, hay and silage crops, and certain cereal grains, are grown specifically for animals. Other feeds, such as sugar-beet pulp, brewers' grains, and pineapple bran, are by-products remaining after a food crop has been processed for human use. Surplus food crops, such as wheat, other cereals, fruits, vegetables, and roots, may also be fed to animals. History does not record when dried roughage or other stored feeds were first given to animals. Most early records refer to nomadic peoples who, with their herds and flocks, followed the natural feed supplies. When animals were domesticated and used for work in crop production, some of the residues were doubtless fed to them. Preservation of green forages such as beet leaves and corn (maize) plants by packing them in pits in the earth has long been practiced in northern Europe. The idea of making silage as a means of preserving and utilizing more of the corn plant was gradually developed in Europe and taken from France to the United States in the 1870s. When the mature, dried corn plant was fed to cattle in the winter, much of the coarse stem was wasted, but when it was chopped and ensiled (made into silage), everything was eaten. The first effort to evaluate feeds for animals on a comparative basis was apparently made by Albrecht Thaer (1752–1828), in Germany, who developed “hay values” as measures of nutritive value of feeds. Tables of the value of feeds and of the requirements of animals in Germany followed and were later used in other countries. Present-day knowledge represents an expansion and improvement of these early efforts. Basic nutrients and additivesThe basic nutrients that animals require for growth, reproduction, and good health include carbohydrates, protein, fat, minerals, and vitamins. The energy needed for growth and activity is derived primarily from carbohydrates and fats. Protein may also supply energy, however, if other sources are not adequate or if it is supplied in great excess above the needs of the body. Animals need a source of energy to sustain life processes within the body and for muscular activity. When the energy intake of an animal exceeds its requirements, the surplus is stored as body fat, which can be utilized later if the energy consumed in food is not adequate. ProteinsAll animals require a small amount of protein for the daily repair of muscles, internal organs, and other body tissues. For immature animals, protein is also needed for growth of the muscles and other parts of the body. Since milk, eggs, and wool contain much protein, additional amounts are needed in the food of animals producing these. Proteins are composed of more than 20 different amino acids, which are liberated during digestion. Animals with simple stomachs, including humans, monkeys, swine, poultry, rabbits, and mink, require correct amounts of the following 10 essential amino acids daily: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, trytophan, and valine. In addition to these, poultry need glycine and glutamic acid for growth. High-quality protein supplied by eggs, milk, fish meal, meat by-products, and soybean meal contains correct amounts of the essential amino acids. Poor-quality protein, such as that in corn grain (maize), contains too little of one or more essential amino acids. Feeds having poor-quality proteins are made useful by blending them with other feeds that supply the lacking amino acids. The quality of the protein in the food is of little importance to ruminants, including cattle, sheep, goats, and the other animals that have four stomachs, because the bacteria that aid in the digestion of food in the rumen (first stomach) use simple nitrogen compounds to build proteins in their cells. Further on in the digestive tract the animals digest the bacteria. By this indirect means, ruminants produce high-quality protein from a food that might originally have contained poor protein, or from urea (a nitrogen compound). Very young ruminants, such as calves, lambs, and kids, however, need good-quality protein until the rumen develops sufficiently for this bacterial process to become established. Carbohydrates and fatsMost animals get energy from carbohydrates and fats, which are oxidized in the body. These yield heat, which maintains body temperature, furnishes energy for growth and muscle activity, and sustains vital functions. Animals need much more energy (and more total feed) for growth, fattening, work, or milk production than simply for maintenance. The less complex carbohydrates (sugars and starches) are readily digested by all animals. The complex carbohydrates (cellulose, hemicelluloses) that make up the fibrous stems of plants are broken down by bacterial action in the rumen of cattle and sheep or in the cecum of rabbits and horses. Such complex carbohydrates cannot be digested by men, or, to any appreciable extent, by dogs, cats, birds, or laboratory animals. Thus, ruminants and some herbivorous animals obtain much more of the energy-giving nutrients from the carbohydrates of plants than the simple-stomached carnivores and omnivores, for which fibrous materials have little or no energy value. Fat in feeds has a high nutritive value because it is highly digestible, and because it supplies about two and one-quarter times as much energy as starch or sugar. While fat has high nutritive value, it can be replaced by an equivalent amount of digestible carbohydrates in the food, except for small amounts of essential fatty acids. Very small amounts of the unsaturated fatty acid linoleic, contained in some fats, are necessary for growth and health. Usual animal feeds, however, supply ample amounts of this acid unless it has been removed by processing. MineralsMinerals essential for animal life include common salt (sodium chloride), calcium, phosphorus, sulfur, potassium, magnesium, manganese, iron, copper, cobalt, iodine, zinc, molybdenum, and selenium. The last six of these are poisonous to animals if excessive amounts are eaten. All farm animals generally need more common salt than is contained in their feeds, and they are supplied with it regularly. Of the other essential minerals, phosphorus and calcium are most apt to be lacking, because they are heavily drawn upon to produce bones, milk, and egg shells. Good phosphorus supplements are bone meal, dicalcium phosphate, and defluorinated phosphates. Egg shells are nearly pure calcium carbonate. Calcium may readily be supplied by ground limestone, ground shells, or marl that is high in calcium. Small amounts of iodine are needed by animals for the formation of thyroxine, a compound containing iodine, secreted by the thyroid gland. A serious deficiency of iodine may cause goitre, a disease in which the thyroid gland enlarges greatly. In certain regions goitre has caused heavy losses of newborn pigs, lambs, kids, calves, and foals. Goitre can be prevented by supplying small amounts of iodized salt to the mother before the young are born. In some areas, soil and forage are deficient in copper and cobalt, which are needed along with iron for the formation of hemoglobin, the oxygen-carrying pigment of the red blood cells. In these areas, farm animals may suffer from anemia unless the deficiency is corrected by means of a suitable mineral supplement. Iron, used in hemoglobin formation, is amply supplied in most animal feeds, except milk. The only practical problem with iron deficiency occurs in young suckling pigs before they start to consume other feeds in addition to milk. Though manganese is essential for animals, the usual rations for all farm animals, except poultry, supply sufficient quantities. A lack of manganese may cause the nutritional disease of chicks and young turkeys called slipped tendon (perosis) and also may cause failure of eggs to hatch. Normal rations for swine are often deficient in zinc, especially in the presence of excess calcium. Adding 100 parts per million of zinc carbonate cures zinc-deficiency symptoms, which include retarded growth rate and severe scaliness and cracking of the skin (parakeratosis). A trace of selenium is necessary for normal health of animals; excessive amounts found in forages in some regions poison animals and may cause death. To furnish both calcium and phosphorus, livestock may be allowed free access to such a mixture as 60 percent dicalcium phosphate and 40 percent common salt. Trace mineralized salt is used when copper or cobalt may be deficient. Animals are given access to common salt separately, so they will not be forced to eat more of the other minerals than they require to get the amount of salt they need. VitaminsKnown vitamins include A, C, D, E, and K, and the B group: thiamine, riboflavin, niacin, pantothenic acid, choline, biotin, folic acid, and vitamins B6 and B12. Vitamin A, the one most apt to be lacking in livestock feeds, is required for growth, reproduction, milk production, and the maintenance of normal resistance to respiratory infections. All green-growing crops are rich in carotene, which animals can convert into vitamin A. Vitamin A supplement is added to animal rations to ensure a supply when they are not on good pasture. Vitamin D enables animals to use calcium and phosphorus; a deficiency causes rickets in young growing animals. The ultraviolet rays of sunlight produce vitamin D from the provitamin in the skin. Field curing of hay develops vitamin D through the action of the sunlight on ergosterol in the hay crops. Certain fish oils are very rich in vitamin D. Livestock that are outdoors in the sunlight much of the time have a plentiful supply of vitamin D. Under winter conditions in cold regions, cattle, sheep, and horses ordinarily get ample amounts from the hay they are fed; laboratory animals may be deficient unless a supplement is added. The vitamin B group is not important in the feeding of cattle, sheep, and other ruminants because the bacteria in the rumen synthesize these vitamins. Very young calves, poultry, swine, and other simple-stomached animals require the B vitamins in their diets. Of these, riboflavin, niacin, pantothenic acid, and vitamin B12 are most likely to be deficient in ordinary feeds; special supplements are needed by pigs, poultry, and laboratory animals. Choline may also be deficient in poultry feeds. Vitamin E is necessary for normal hatching of eggs. It plays a role along with selenium in preventing muscle stiffness and paralysis (dystrophy) in lambs, calves, and chicks under certain conditions. Vitamin C, which prevents scurvy in humans and guinea pigs, can be synthesized in the bodies of other animals and need not be supplied in their food. Vitamin K is synthesized by bacteria in the intestinal tract; a dietary supply is usually not important. Antibiotics and other growth stimulantsSince about 1950, antibiotics have been added to diets of growing animals because they increase the rate of growth and decrease death loss. Those most commonly used are chlortetracycline, oxytetracycline, bacitracin, and penicillin. An antibiotic helps to overcome the growth-depressing effects of an inadequate diet or of imperfect management practices, but its effectiveness differs among animal species. Diethylstilbestrol, testosterone, progesterone, estradiol, and dienestrol in various combinations are administered orally or subcutaneously to stimulate growth of cattle and sheep for meat production. Composition and valuation of feedsThe usual chemical analyses of feeds provide information on the amount of dry matter, protein, fat, fibre, and ash contained in the feed. Energy value, mineral elements, and vitamins are also determined; these values are included in complete tables of feed composition. DeterminationDigestion and balance experiments measure the degree to which the various components of a feed are absorbed and retained by the animal body. Protein requirements are expressed as the amounts of digestible protein needed for growth or other body functions. The amounts of energy needed are measured as digestible energy (DE), metabolizable energy (ME), net energy (NE), or total digestible nutrients (TDN). The total gross energy value of a feed is the amount of heat liberated when it is burned in a bomb calorimeter. Only a part of this energy is available to the animal because some passes through the body without being digested. Furthermore, some of the DE is not utilized but is excreted in the urine as urea. There is a further energy loss from the ME as heat of fermentation and as gas produced by bacteria in the digestive tract. This loss is appreciably greater in ruminants than in pigs, chickens, or other nonruminants. The work of eating, digesting, and metabolizing food may also be subtracted from the food energy, resulting in the NE, or useful energy value of a food. The TDN value of a feed represents the sum of the digestible protein, digestible fat × 2.25, digestible nitrogen-free extract, and digestible fibre. This measure is less useful than NE because it considers neither the fermentation and heat losses during digestion and metabolism nor the fact that energy is utilized more efficiently for maintenance or milk production than for growth and fattening. Optimization of nutrient-cost ratioFeed costs vary widely from season to season; it is often possible for producers to realize substantial savings by wise selection of the feed ingredients used to formulate complete rations. It is much easier for large commercial feed companies with operations in different regions to take advantage of low costs than it is for individual relatively small-scale livestock producers. Least-cost programming of feed mixtures makes it possible to use electronic computers for selecting the correct amounts of the lowest-cost feed ingredients that will fully satisfy the nutrient requirements of a specific type of animal at a particular stage of development. The system has successfully formulated highly palatable rations that yield maximum production at lowest cost. As in other areas of agriculture, the large-scale producer, with the ability to purchase and operate advanced systems, has an economic advantage. Basic types of feedsAnimal feeds are classified as follows: (1) concentrates, high in energy value, including (a) cereal grains and their by-products (barley, corn [maize], oats, rye, wheat), (b) high-protein oil meals or cakes (soybean, cottonseed, peanut [groundnut]), (c) by-products from processing of sugar beets, sugarcane, and (d) animal and fish by-products; (2) roughages, including (a) pasture grasses, (b) hays, (c) silage, (d) root crops, and (e) straw, stover (stalks). The composition of a few of the most commonly used feeds is shown in Tables 1 and 2. Concentrate foodsCereal grains and their by-productsIn the agricultural practices of North America and northern Europe, barley, corn (maize), oats, rye, and sorghums are grown almost entirely as animal feed, although small quantities are processed for human consumption as well. These grains are fed, whole or ground, either singly or mixed with high-protein oil meals or other by-products, minerals, and vitamins, to form a complete feed for pigs and poultry or an adequate dietary supplement for ruminants and horses. The production of grains is seasonal because of temperature or moisture conditions or a combination of both. It is necessary to produce a full year's supply during the limited growing season. The grain is dried to prevent sprouting or molding; the grain is then stored in containers or buildings where insects and rodents cannot destroy it. It is generally desirable to store more than a year's supply of the grains to be used as feed, because crop failures sometimes occur. High-protein mealsVegetable seeds produced primarily as a source of oil for human food and industrial uses include soybeans, peanuts (groundnuts), flaxseed, cottonseed, coconuts, oil palm, and sunflower seeds. After these seeds are processed to remove the oil, the residues, which may contain from 5 percent to less than 1 percent of fat and 20 to 50 percent of protein, are marketed as animal feeds. Cottonseed and peanuts have woody hulls or shells, which are generally removed before processing—if the hulls or shells are left intact, the resulting by-product is higher in fibre and appreciably lower in protein and energy value. These feeds are used as supplements to roughages or cereal grains and other low-protein feeds to furnish the protein needed for efficient growth or production. The supplement chosen for a particular ration depends largely upon the cost and availability of supply. By-products of sugar beets, sugarcaneFrom the sugar-beet industry come beet tops, which are used on the farm either fresh or ensiled, and dried beet pulp and beet molasses, which are produced in the sugar factory. Cane molasses is a residue from cane-sugar manufacture. These are all palatable, high-quality sources of carbohydrates. Sugarcane bagasse (stalk residue) is fibrous, hard to digest, and of very low feed value. In some European countries fodder beets and some other roots are grown as animal feed. Citrus molasses and dried citrus pulp, which are generally available at low cost as by-products of the citrus-juice industry, are often used as high-quality feeds for cattle and sheep. Other by-product feedsBy-products or residues from commercial processing of the cereal grains to produce human food supply large quantities of animal feeds. The largest group of these comprises feeds derived from the milling of wheat in the production of flour including wheat bran, wheat middlings, wheat-germ meal, and wheat-mill feed. In some areas bakery wastes, such as stale and leftover bread, rolls, and various pastry products, are ground and used as filler or feed for pets and farm animals. Rice bran and rice hulls are obtained in similar fashion from the mills that polish rice for human food. Corn gluten feed, corn gluten meal, and hominy feed are produced as by-products from the manufacture of starch for industrial and food uses. Brewers' grains, corn-distillers' grains, and brewers' yeast are useful animal feeds and are collected from the dried residues of the fermentation industries that produce beer and distilled spirits. Waste products from pineapple-canning plants include pineapple bran or pulp and the ensiled leaves from the plant. By-products from the abattoirs and meat-packing plants that process animals into meat include such feeds as meat and bone meal, tankage, meat scraps, blood meal, poultry waste, and feather meal. Dried skim milk, dried whey, and dried buttermilk are feed by-products from the dairy industry. Various types and qualities of fish meals are produced by the fish-processing plants. These feeds contain 50 percent or more of high-quality protein and the mineral elements calcium and phosphorus. Steamed bone meal is particularly high in these important minerals. RoughagesPasturePasture grasses and legumes, both native and cultivated, are the most important single source of feed for cattle, horses, sheep, and goats. During the growing season they furnish most of the feed for these animals at a cost lower than for feeds that need to be harvested, processed, and transported. Hundreds of different grasses, legumes, bushes, and trees are acceptable as feeds for grazing animals. The nutritive value of the cultivated varieties has been studied, but information is incomplete for many of those that occur naturally. The composition of some of the forage crops most widely used is shown in Table 2. HayHay is produced by drying grasses or legumes when they approach the stage of maximum plant growth and before the seed develops. This stage has been shown to give maximum yields of digestible protein and carbohydrates per unit of land area. The moisture content must be reduced to 22 percent or less to prevent molding, heating, and spoilage during storage. Legume hays, such as alfalfa and clovers, are high in protein, while the grasses (such as timothy and Sudan grass) are lower in protein but vary considerably depending upon the stage of maturity and level of nitrogen fertilization applied to the crop. Stored hay is fed to animals when sufficient fresh pasture grass is not available. SilageSilage is made by packing immature plants in a storage container to exclude the air and allow fermentation to develop acetic and other acids, which preserve the moist feed. Storage may be in upright tower silos or in trenches in the ground. Best quality silage results when the forage is ensiled with a moisture content of 50 to 65 percent. Lower moisture levels can cause difficulty in obtaining sufficient packing to exclude air and may result in molding or other spoilage. Too high a moisture content causes nutrient losses by seepage and results in the production of excessively acid, unpalatable silage. Ensiled forage can be stored for a longer period of time with lower loss of nutrients than dry hay. The nutritive value of silage depends upon the type of forage ensiled and how successfully it has been cured. Corn (maize), sorghums, and grasses, and sometimes leguminous forages, are used in making silage. Root cropsThese are used less extensively as animal feed than was true in the past, for economic reasons. Mangels, rutabagas, cassava, and sometimes surplus potatoes are used as feed. As shown in Table 2, they are lower in dry-matter content than are most of the other feeds listed. They are relatively low in protein also and provide mostly energy. Straw and hullsQuantities of straws remaining after wheat, oats, barley, and rice crops have been harvested are used as feed for cattle and other ruminants. The straws are low in protein and very high in fibre; digestibility is low. Straw is useful in maintaining mature animals during periods of shortage of other feeds, but it is too low in quality to be satisfactory for long periods without being supplemented with other feeds to supply the protein, digestible energy, and minerals needed for growth and production. Treatment of straw with alkali markedly increases the digestibility of the cellulose, augmenting its value as a source of energy for animals. Corncobs, corn stalks, cottonseed hulls, and rice hulls can also be used as sources of fibre in ruminant rations. Rice hulls are lower in value, while the others are similar to straw. |