The possibility of a relationship between vitamin A intake and ascorbic acid metabolism and reproduction has been suggested. P. H. Phillips and his associates at the Wisconsin Agricultural Experiment Station reported lower blood plasma and urine ascorbic acid values in a calf on a vitamin A-deficient ration than in a check animal that received 100 micrograms of carotene per kilogram of body weight. Later, they found that the feeding of a high potency shark-liver oil to certain dairy herds in a breeding cooperative caused the animals to maintain more nearly normal ascorbic acid values in the blood plasma. In studies conducted at the Maryland station it was found that ascorbic acid excretion was depressed in severe vitamin A deficiency, but not in moderate deficiency. These data raised the question of whether, under practical conditions, the vitamin A intake is not always sufficient to prevent any marked depressing effect on ascorbic acid synthesis. If there were a deficiency it would indirectly affect reproduction. Vitamin A deficiency does affect reproduction; severe deficiency will cause sterility or poor conception rates, but a study of the available scientific data does not lead to the conclusion that this would be true under practical farm conditions. The scientists at the Oklahoma station obtained a satisfactory conception rate when the carotene intake was at the same level as that required for normal calving. Data collected at Beltsville do not indicate that the conception rate was any lower for cows on poor hay than for those on good hay.

The need of bulls for carotene for proper reproductive performance has not been worked out in detail. Experiments with various species of animals, including the bull, have shown that vitamin A deficiency causes a degeneration of the germinal epithelium of the testicles. At Beltsville semen capable of fertilizing cows was produced by young bulls that had developed rather severe symptoms of vitamin A deficiency, such as blindness, incoordination, weakness, or diarrhea. The intake of these bulls was less than 10 micrograms of carotene per pound of body weight. Blindness will usually develop in growing bulls on an intake of 10 micrograms or less of carotene per pound of body weight. Although the semen of the bulls at Beltsville could impregnate cows, it did not maintain motility after storage, was low in concentration of sperm, and was in general of poor quality. Nor did the young bulls kept on these low intakes start to breed at the normal age. This sexual retardation appeared to depend on the age at which the bulls developed vitamin A deficiency. A cow needs an ample supply of carotene to produce normal calves. The amounts given here are double the minimum required, but are recommended for best results.

According to data collected at the Maryland station, young bulls 12 to 14 months old reared on intakes of carotene varying from 10 to 34 micrograms per pound of body weight and kept outside during the heat of the summer showed marked histological alterations in the testicles. Increasing the intake of carotene to 100 micrograms per pound of body weight brought about marked improvement.

It seems unlikely, under practical farm conditions, that vitamin A will be a limiting factor of great importance in affecting the reproductive performance of bulls. It does seem likely that if hay were fed to them in the same quantities as for growing dairy cattle, the intake of carotene would be sufficient to maintain proper reproductivity in bulls.

THE AUTHORS

L. A. Moore, in the Bureau of Dairy Industry, has made several outstanding contributions in dairy cattle nutrition, his greatest being the correlation of increased cerebrospinal fluid pressure with vitamin A deficiency. He has also developed a method for determining the amount of carotene in hay and silage and has studied the effect of maturity on the carotene of some of the common hays and pasture plants.

Henry T. Converse, in the same Bureau, has investigated vitamin A requirements for growth, lactation, and reproduction in dairy cattle; calcium requirements for growth and milk production; and the role of some other vitamins than vitamin A in calf growth.

Among the important investigations made by S. R. Hall in the Bureau of Dairy Industry has been the effect of the low vitamin A in the ration on the anterior pituitary gland and reproduction in cattle.