Vitamin A for Dairy Cattle

by L. A. MOORE, HENRY T. CONVERSE, and S. R. HALL

TOO LITTLE vitamin A in rations of dairy cattle leads to difficulties that sometimes a farmer cannot readily tell from ailments produced by other causes. Young calves that do not get enough vitamin A the first 3 or 4 months usually die of scours and pneumonia. If they survive early calfhood and their vitamin A intake is exceptionally low, they are apt to show poor condition, grow slowly, become blind, and have diarrhea and convulsions. Even though enough vitamin A is fed to produce good growth and apparently healthy calves, there still may be a partial deficiency; that can be detected only by directly examining the inside of the eye or by determining the vitamin A content of the blood plasma, which will be low. Cows that get too little of the vitamin reproduce poorly, as denoted by premature births, still-born calves, and retention of the afterbirth. The deficiency must be severe, however, to lower potency of bulls. Other symptoms of vitamin A deficiency are quite noticeable before semen quality and sexual urge are affected.

Except for the first few months of life, depending on the length of the whole-milk feeding period, dairy cattle receive most of their vitamin A in the form of carotene, a yellow pigment in plant material. Carotene is the same pigment that gives the yellow color to carrots and the natural color to butter. In hay and other roughages the yellow color is masked by the green pigments in the plant. The yellow pigment, carotene, sometimes called provitamin A, is changed by the animal body to the true vitamin A, which is almost colorless. The vitamin A in cod-liver oil is the same material as that formed from carotene in the animal body. Young calves receive a considerable supply of the colorless form Of vitamin A in the cow's first milk ( the colostrum) , whole milk, or when their ration is supplemented with cod-liver oil.

Quantities of vitamin A and carotene are usually expressed in terms of micrograms, a unit of weight that denotes one-millionth of a gram or about one twenty-eighth of a millionth of an ounce. One can readily appreciate the extremely small quantities of material with which we are dealing when we talk about vitamins. The term "International unit," abbreviated I. U., also is used. One I. U. equals about 0.25 microgram of vitamin A or 0.6 microgram of Beta-carotene in biological activity. A milliliter, another unit used in measuring volumes, equals about one-fifth of a teaspoon.

Calf Diets Have Changed

Present-day methods of raising dairy calves with limited amounts of whole milk have considerably altered the quality and quantity of food that a young calf receives, compared with what calves received in the wild state.

What happens is told in reports from several State agricultural experiment stations.

Maryland: When calves were fed limited amounts of whole milk, the vitamin A content of the blood plasma from birth to 4 months of age was in the deficient range, as judged by blood values of older calves that had too little vitamin A.

Michigan : The vitamin A content of the blood plasma of dairy calves getting limited quantities of whole milk was one-third lower than that of beef calves of the same age that obtained considerable whole milk by suckling.

Ohio : The incidence of pneumonia declined in calves that received 15,000 I. U. of vitamin A concentrate daily.

Minnesota: Less trouble from digestive disturbances was encountered in young calves fed cod-liver oil than in calves not receiving the supplement. Whole milk was fed at the rate of one-eighth of the body weight for the first 30 days, followed by skim milk to 6 months of age. While both groups had scours, some of the calves that had no supplement died.

Wisconsin: The administration of shark-liver oil, of high vitamin A Potency, plus certain of the B vitamins, eliminated diarrhea and lowered the number of deaths from pneumonia.

Michigan : Young calves invariably died of pneumonia and scours when placed on a vitamin-A-deficient ration.

Beltsville: Calves on a low vitamin A intake all died before they were 100 days old.

The reports suggest that vitamin A may have something to do with the building-up of an immunity against bacterial infections in young calves.

H. T. Converse and E. B. Meigs, in studies at Beltsville, used a ration low in vitamin A, consisting of skim milk, grain, and late-cut brown timothy hay. Their results indicate that a minimum intake of between 10 and 25 micrograms of vitamin A per pound of body weight a day is necessary to maintain normal growth.

It is possible that vitamin A is more important to a herd in which the organisms that cause pneumonia and scours are present than to one where the organisms are absent or nonvirulent. In the latter case, a very low intake of the vitamin might cause no difficulty. In evaluating the tests and results, therefore, these points must be kept in mind.