Another discovery is that cow manure is a valuable source of vitamins for chickens and turkeys. This subject was first investigated because it had been shown that bacteria in the rumen (the first and largest stomach of cattle) can synthesize thiamine, riboflavin, and several other vitamins. Our experiments showed that the addition of cow manure (dried at 45° C.) to a low-grade diet enhanced the growth of chicks and stimulated comb growth. Its addition to a low-grade diet for laying hens decreased egg production but increased hatchability. Drying the cow manure at 80° C. destroyed the factor that stimulated comb growth and decreased egg production, but did not destroy the factor that improved the growth of chicks and increased hatchability. We did not find these favorable effects when we added the manure to an already adequate diet. The low-grade diets contained no animal protein supplements. They were improved to about the same extent by adding either dried cow manure or fish meal as 5 percent of the diet.

This new knowledge interested us tremendously. Besides its own basic, practical value, the discovery exemplifies a truth about the nature of modern science : Farmers had no need to give it thought during the centuries that chickens ran freely in barnyards, eating what manure they wanted; now, when countless broilers are raised in batteries and never even touch the ground, we see the merit of an old practice.

We went on experimenting. We learned that the growth-promoting effect of cow manure was due to an unknown factor in it, not to the presence of any of the known vitamins. We also demonstrated that this mysterious factor is synthesized in the digestive tract of mature chickens and is present in their excrement in about the same concentration as in cow manure. Hence, the rumen is not essential to its synthesis.

Cow manure was used as a starting material for the preparation of concentrates of the growth-promoting factor. The most potent concentrates thus far prepared were effective when fed as 0.004 percent of the diet, and thus were about 1,000 times as effective as dried cow manure or fish meal. Tests on both the white and dark meat of chickens whose feed was up to 10 percent dried manure failed to disclose any undesirable odors or flavors. Notwithstanding the encouraging results obtained, the use of cow manure as a source of vitamins is not yet advised by the Department, pending further research. We must know more about the possibility of spreading diseases.

To go back to soybean meal : In studies of hatchability, we found that, without animal protein, the hatchability and viability of chicks go down as the level of soybean meal in the hens' diet goes up. This effect of soybean meal is overcome by feeding the hens animal protein of high quality, such as fish meal and dried-milk products, and also by feeding dried cow manure. When adequately supplemented with these materials, the total diet of breeding birds may contain 10-percent soybean meal.

We wanted to know how the amount of feed a hen eats affects the number of eggs she lays. When we cut the quantity of feed to 87.5 and 75 percent of the normal consumption, the hens cut their production 25 and 50 percent, respectively. Cutting down on feed this way, however, did not affect the size of eggs or the live weight of the birds. But since efficiency of egg production depends so largely on rate of production, it follows that reducing the feed for laying hens cuts their efficiency.

Other experiments indicate that increasing the fiber content of diets of laying hens from about 2.5 percent to about 6 percent decreases by about 16 percent the efficiency with which hens utilize feed.

Artificial incubation and brooding, increasingly popular systems that keep large numbers of chicks together, are apt to cause more feather picking, toe picking, and cannibalism, vices that sometimes cause heavy losses. They can usually be stopped by giving the chicks more salt in their feed. Adding 2 percent of salt to an all-mash diet or 4 percent to a mash fed with a grain or grain mixture for 2 or 3 days is recommended.

A high proportion of corn in the diet increases the chicken's need for nicotinic acid. That seems true also of human diets, since pellagra, the disease due to deficiency of nicotinic acid, is likely to occur among people who subsist largely on corn. Meats are good sources of nicotinic acid; chicken meat has been found to be outstanding in this respect. The light meat and liver contain as much nicotinic acid as beef and pork liver, which are often recommended as the best sources of the vitamin; dark chicken meat contains slightly more nicotinic acid than beef and pork.

In feeding turkeys, fish oils of all kinds should be omitted from the diet after the birds reach 8 weeks of age. When such oils appear to be necessary in the diet of turkeys older than 8 weeks, the quantity should not exceed one-eighth of 1 percent. The quality of the oil should be high and it must not be rancid. Fish meals also should be omitted or sharply restricted in the diet of turkeys older than 8 weeks.

Color has little bearing on the nutritive value of poultry products. But it does affect their appearance and must be considered as a quality factor. The yellow pigments of egg yolk and of the shanks and skin of chickens are related chemically to vitamin A, but the pigments present in greatest quantity have no vitamin A potency. It was demonstrated some time ago at Beltsville and the University of Maryland that some feedstuffs contain substances that interfere with the laying down of yellow pigment. More recent work showed that vitamin A itself produces such an interfering effect when present in large quantities. Vitamin A is practically always present in poultry feeds and in egg yolk, but whether it interacts with the yellow pigments when present in the usual quantities remains to be investigated.

In the case of feather pigmentation, researchers at the University of California and in industrial laboratories found that pantothenic acid and folic acid are needed for the development of black pigment; scientists at the University of Maryland learned that deficiency of vitamin D increases the production of black pigment.

THE AUTHOR

H. R. Bird is a biochemist in charge of Poultry Nutrition Investigation at the Bureau of Animal Industry. For approximately 5 years prior to 1944 he was associate professor of poultry nutrition at the University of Maryland. Dr. Bird is a graduate of the University of Wisconsin.