The Role of Vitamins in Animal Feed

Known vitamins include the fat-soluble vitamins A, D, E, and K, and the water-soluble B group of thiamin, riboflavin, niacin, pantothenic acid, choline, biotin, folic acid, and vitamins B₆ and B₁₂ and vitamin C.

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 diets to ensure a supply when livestock are not fed green forages and 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; pigs, poultry, and laboratory animals that are raised indoors will 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 their rumen synthesize these vitamins. Very young calves, however, and poultry, swine, and other monogastric 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 the 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 most other animals and need not be supplied in their food. Vitamin K is synthesized by bacteria in the intestinal tract and can be absorbed, and, if livestock can ingest feces, a dietary supply is usually not important. Today many animals are raised without fecal contact, though, so vitamin K is often added to their diets as a safety factor.