New Knowledge About Feeding

Studies at a number of stations provide new information on the feed horses need. In tests with Percheron geldings, A. L. Harvey, B. H. Thomas, C. C. Culbertson, and E. V. Collins, of the Iowa station, showed that horses weighing about 1,700 pounds at light, medium, or heavy work probably do not receive enough calcium and phosphorus either in a maintenance ration of 3 pounds of oats and 20 pounds of timothy hay, or in the same ration plus sugar and dextrinized starch, which give energy.

At the University of California, C. E. Howell, G. H. Hart, and N. R. Ittner found that rations commonly fed to horses in areas where yellow corn is not available are apt to be deficient in vitamin A, a deficiency that leads to night blindness. Accompanying that condition they also found a joint ailment that causes lameness, which they later discovered is not due to vitamin A deficiency. In speculating on the significance of that finding, Dr. Hart pointed out that green feed may contain a vital dietary factor that helps prevent lameness. He recalls that in the days of horse cars, the car horses had to be taken out of regular service for a rest on summer pasture from 2 to 7 weeks, and that British horse trainers provide green feed near their training stables to prevent lameness, which is so fatal to success in racing.

Tests at the Army Remount Veterinary Research Laboratory at the Front Royal Remount Depot in Virginia showed that the use of riboflavin in rations effectively prevented periodic ophthalmia, or moon blindness, a malady responsible for more blindness in horses than all other causes combined. Forty milligrams of crystalline riboflavin, a member of the vitamin B complex, was fed to each horse daily with the grain ration, at a cost of a cent a day. From November 1943 to June 1944 no cases of moon blindness occurred among 130 horses that received the supplement, but new cases occurred annually at the rate of 109 per thousand horses among those not receiving it. Riboflavin is now given all horses at the depot. Whether ophthalmia is purely a nutritional disease is still an open question, however. Further research is needed.

We have also learned a great deal about reproductive processes in stallions and mares. V. R. Berliner, at the Mississippi station, reported that stallion and jack sperm cells stay alive inside the female for only a day or so, and for only a matter of hours in storage without the addition of some life-prolonging and diluting medium known, as a diluter. Bull sperm survive 2 days or more in the female, and longer outside. The differences in longevity between the stallion or jack sperm cells and bull sperm cells are apparently due to the high glucose content of bull semen that the sperm convert into lactic acid. The acid depresses the life processes of the spermatozoa and brings about a resting stage from which they can later be restored to motility. Semen of stallions has a relatively high salt content, which acts as an overstimulant to the sperm and causes their rapid exhaustion and death.

Dr. Berliner evolved a gelatinized glucose-tartrate egg-yolk diluter with which it was possible to effect pregnancies in mares with 48-hour old semen. However, he advocates the use of semen preferably not more than 6 to 8 hours old. The requirement that semen be fresh would limit the practice of artificial insemination of mares to relatively small areas, or to points having good air-transport connections.

Dr. Berliner points out further that artificial insemination, although sometimes useful, cannot increase pregnancies over the natural capacities of the mare and the stallion, and that the highest percentages of pregnancies are probably obtained by turning stallions and mares together on pasture or range. He found also that sperm production by stallions and jacks declined when the animals became overfat, and that sperm produced by sires fed on corn were of low viability, thus verifying an old saying, "There are no foals in corn." In his experiments, good pasturage overcame the bad effects of an overfattening grain ration, which was also low in vitamin content and in mineral balance.

Experiments at the Michigan station throw light on at least one of the qualities of pasture that make it a valuable feed for breeding animals. It was found that blood ascorbic acid values for good breeders, in mares of both heavy and light breeds, were significantly higher than those of poor breeders, and that the ascorbic acid content of the blood of mares varied directly with their access to good pasturage. In the spring before the mares were turned on pasture, .09 mg. of ascorbic acid was found per 100 ml. of blood plasma. This value rose to. 17 mg. on spring pasture, fell to .11 mg. on summer pasture, rose again to .14 mg. on fall pasture, and fell to. I I mg. during the winter. Injections of ascorbic acid (vitamin C) into a 3-year-old Belgian stallion whose semen- showed almost an absence of sperm and no sperm motility, raised the sperm count to between 2 billion and 4 billion and the motility to approximately 70 percent activity. Later this same stallion was fed ascorbic acid by capsule, at the rate of one gram daily, with equally good results.

Good results were had at the Mississippi station from using the synthetic estrogen stilbestrol in inducing heat in mares that were shy breeders. The treatment induced heat 5 days after injection. Ovulation followed in 4 or 5 days. The treated mares were bred on the second and fourth day of heat, and became pregnant.

Many horse breeders believe that the surest time to get a mare with foal is to breed her during foal heat, which occurs on about the ninth day after foaling, and lasts 1 day. Dr. Berliner strongly advises against this practice on premises where breeding diseases resulting in abortions and losses of newborn foals have occurred. At this time, the mare's uterus usually has not had time to recuperate from parturition, and is much more vulnerable to infection. Records kept at large breeding farms show higher percentages of navel ill, joint ill, and other prenatal diseases in newborn foals when the pregnancies occur during foal heat than when the mares are bred at later heat periods.

Other findings also confirm that only strong, healthy mares should be bred during foal heat. Dr. Hart and his colleagues in California learned that pregnancies that required a large number of services per conception were followed by long gestations and resulted in high percentages of foals born dead—another indication that the mare's sex organs may not be entirely sound for some time after parturition. A competent veterinarian should examine the placenta of each foaling mare to determine the best time to mate her, especially if there are any signs of infection or other abnormal conditions.

Foalings in winter and early spring were found to follow longer gestation periods than did summer and fall foalings, probably because of the lower nutritive value of feed during the seasons of scant pasturage at the time the fetus is at a rapidly growing stage. A healthy foaling mare is one that shows no important necrotic lesions of the placenta, has not retained her placenta longer than 6 hours, has a healthy vigorous foal, and has not carried her foal longer than 340 days when foaling from December to May, nor longer than 334 days for June-to-November foalings.

THE AUTHOR

William Jackson is assistant chief of the Animal Husbandry Division in the Bureau of Animal Industry. Among his more recent publications is a textbook on Livestock Farming prepared specifically for men who chose to study the subject while in the armed forces. He is a graduate of Purdue University.