plant and animal products, as well as mineral matter, used to feed farm animals. Feeds provide animals with the nutrients they need to maintain their vital functions, growth, and productivity. They must contain easily digested nutrients, must be readily eaten, must not have harmful effects, and must be physically and chemically compatible with the anatomical and physiological characteristics of the animals.

The classification of feeds is based on their origin and main properties. Plant feeds, including green and coarse feeds, silage, haylage, roots and tubers, grain, plant by-products, and mixed feed, are the most widely used. Green feed, such as grasses from natural and sown pastures, plants grown for green feed, and tops of roots and tubers, constitutes the major portion of the diet of ruminants in summer. Coarse feed—hay, straw, chaff, and corn cobs—contains a substantial amount of cellulose, which ruminants need for digestion. Good hay is one of the principal feeds for ruminants in winter. Haylage, a preserved feed made from dried grasses, can replace hay and silage in the diet of ruminants. Grass meal, feed made from artificially dried legume grasses and mixtures of legumes and cereals, is used as a protein and vitamin supplement. Silage is a succulent feed given to all animals in winter; in summer it is used as a supplement. Root and tuber crops (beets, carrots, turnips, potatoes, rutabagas) and such succulent feeds as pumpkins and citronmelons are readily eaten by all animals. The dry matter of these feeds is rich in digestible carbohydrates, vitamin C, and carotene (yellow varieties). Grain feeds include cereals (oats, barley, corn) and legumes (peas, beans, lentils). Cereal grains contain a great deal of carbohydrates, chiefly starch, whereas legumes are rich in high-quality protein. The most valuable plant by-products include those of milling (bran, mill grain chops, meal dust), sugar beet processing (bagasse, molasses), oil extraction (oil cake, oil meal), starch production (vegetable pulp), and alcohol distilling and brewing (brewery mash, brewers’ grains, malt sprouts). The nutritive value of these feeds depends on the quality and type of raw material used and on production techniques (grinding, extraction of oil from the seeds of oil-bearing plants).

Plant feeds are divided into bulk and concentrate feeds, de-pending on their chemical composition and their physiological effect on the animals. Bulk feeds contain no more than 0.5 kg of digestible nutrients (0.65 feed unit) per kg of feed and include coarse and succulent feeds, as well as watery by-products of the starch, beet sugar, and fermentation industries. Coarse feeds contain more than 19 percent cellulose and the other bulk feeds more than 40 percent water. Concentrate feeds contain more than 0.5 kg of digestible nutrients (more than 0.65 feed unit) per kg of plant feed.

Animal feeds include whole and skim milk, buttermilk, fish meal, meat-and-bone meal, blood meal, and other animal products used to feed animals. They have a large amount of high-quality protein and are rich in minerals and vitamins. They are used to feed all young animals, as well as adult swine, poultry, and fur-bearing animals.

The most widely used mineral feeds are salt, a source of sodium and chlorine; chalk, limestone, and shells, providing calcium; bone meal and defluorinated phosphates, sources of calcium and phosphorus; and urea, a nitrogen compound.

Mixed feeds are prepared by combining various feeds. Also manufactured are enriching mixtures of biologically active substances formed by biological and chemical synthesis; these take the form of premixes, protein-vitamin-mineral supplements, nutrient yeasts, and amino acids. Whole milk substitutes are feed mixtures used in rearing calves. Skim milk is the basis of these substitutes, and other essential components are fat (animal or vegetable), vitamins, antibiotics and, if necessary, trace elements.

Food wastes, the kitchen wastes of restaurants and urban dwellers, are used to feed swine. Their food value varies with the type of wastes and the way in which they are collected.

The economic value of feeds is determined by their nutritive value, dietetic properties, and the cost of producing a single feed unit. The nutritive value varies with the chemical composition and digestibility of the nutrients and with the mineral and vitamin content.

The amount of protein (protein and nonprotein nitrogen compounds) and its quality and digestibility are important factors in the quality of feed. The quality of protein is determined by the amino acids, primarily the essential ones, that it contains. Feeds with less than 100 g of digestible protein per feed unit have insufficient protein; those containing more than 100 g of digestible protein are high in protein. Feeds rich in protein include legume seeds (20-30 percent), oil cakes (30-40 percent), young pasture grass, good hay from legumes, and feeds of animal origin. Straw, especially from rye, hay from mature grasses, root and tuber crops, and dehydrated bagasse are low in protein.

Plant feeds are low in fat: 4—5 percent in corn and oats grains, 1-2 percent in other cereal grains and in peas and vetch, 0.5-1 percent in green chop, and 2-3.5 percent in oil-seed meal. The richest in fat are the seeds of oil-bearing crops (30-40 percent), soybeans (15-16 percent), and oil cakes (6-9 percent). Fat is especially important in the diet of animals with simple stomachs and of calves in the first months of life.

Nitrogen-free extracts include a variety of substances of which starch and sugar are the most valuable. Starch accumulates in seeds, fruits, and tubers, where it constitutes up to 70 percent of the dry matter. There is little starch in the stems and leaves (about 2 percent). Grain feeds and tuber crops are rich in starch, and cucurbits, root crops (sugar beets about 20 percent), and green grass chop are rich in sugars. The milk of domestic animals contains 3-6 percent lactose.

Cellulose has a considerable effect on the digestibility and nutritive value of feeds. The amount of cellulose and its chemical composition depend on the age of the plant (it is less abundant but more digestible in young plants). As the plant matures its cell walls thicken and become more woody, the amount of lignin increases, and digestibility decreases. The amount of cellulose varies from one part of the plant to another; there is more in the stems and less in the leaves, fruits, and tubers. Straw contains 30-40 percent cellulose, hay 25-30 percent, green feed and silage 5-10 percent, and roots and tubers 0.6-1.5 percent. Cellulose is necessary for all animals, but especially for ruminants.

Among essential minerals in feeds are calcium, phosphorus, sodium, potassium, sulfur, chlorine, and, in areas deficient in trace elements, cobalt, iodine, copper, manganese, zinc, and iron. It is important to know the total amount of alkaline and acid elements in feeds. Legumes exceed grasses in calcium content, and oil cakes and oil-seed meal are rich in phosphorus. The essential vitamins are provitamin A, or carotene (abundant in young grass, good hay, red carrots, some cucurbits), the vitamin B group (abundant in legume grasses and cereal grains), and vitamin D (abundant in irradiated feed yeasts).

The composition and nutritive value of feeds depend on many factors, chiefly the conditions under which the plants are grown (climate, soil, fertilizers, farming practices), plant variety, the age of the plant at the time of harvesting, the method of harvesting, and storage conditions. Feeds are analyzed to determine their nutritive value and quality. On farms they are evaluated by such external characteristics as color, odor, and shape. The suitability of a feed for a particular kind of animal and its effect on the quality of production are also taken into account. Feed must be of good quality. Moldy, rotten, frozen, or contaminated feed causes diseases in animals.

The standards for composition, nutritive value, and external characteristics of feed are set by GOST (All-Union State Standards). Various methods of preservation (drying, ensiling), granulation, and briquetting are used to prolong storage and facilitate machine distribution of feed. On farms feed is treated in various ways to make it more edible and digestible. Tables showing the nutritive value of various feeds are available.