Litter reduces the danger of coccidiosis. As another protection against it, fill in low places around brooder houses with clean gravel. Also helpful in lowering mortality of chicks is ample light in brooders. Without good light many chicks will not learn to eat and drink, and losses will be high. The color of the light is much less important than the intensity. Studies show, however, that neither color of light nor its intensity during the first 16 weeks has any effect on the final live weight, egg production, or the fertility or hatchability of eggs.

The use of artificial lights to supplement natural daylight, especially in winter, has been the subject of much discussion among poultrymen. Artificial lights have been observed to affect both molting and egg production of mature stock. Most molting hens resume egg production under the stimulus of artificial light. During a 3-month molt period ( December, January, and February) the rate of production of experimental birds receiving artificial light was about 40 percent—signifying an average of four eggs in 10 days. By contrast, the rate for control birds that received only natural winter daylight during the same period was about 15 percent. No known light stimulus, however, affects the normal one-egg-a-day limit to a hen's egg production.

Turkeys also respond well to artificial lighting, and by its use they can be made to produce hatchable eggs during the fall and winter, thus lengthening the egg-producing season.

Poultrymen have learned to hatch chicks in January, February, and March so that they reach sexual maturity in September, October, and November, the period of shortest egg supply. Day length is sufficient to support egg production in well-grown pullets during these months.

Many pullets that start to lay in early fall molt during the short winter days. These pullets and molting hens in good flesh can be kept in production by lengthening the day with artificial light if their feed intake and body weight are normal. Hens that lose weight do not respond readily to increased light.

Regulating the time of hatch is important with respect to egg weight, too. Pullets 5 months old in July sometimes start laying heavily before they are big enough to produce eggs of good market size. There is a negative relation between length of day at sexual maturity and age and body weight at sexual maturity. Pullets that begin to lay in December without artificial light are older, heavier, and lay larger eggs than those that start to lay in September. We do not know whether sexual maturity of early hatched pullets can be delayed by artificially shortening day length during the summer months until they reach a good body weight.

Light is one of the external factors regulating the hen's hormone secretion. Physiological processes involved in egg formation are under direct hormonal control. Thus, the pituitary gland, at the base of the brain, is stimulated by light acting through the eye to produce certain hormones. These hormones are carried by the blood that goes to the ovary or testis, causing them to grow and ripen eggs or sperm. The ovary, or testis, is also stimulated by these pituitary hormones to produce sex hormones, which cause the comb and oviduct to grow and regulate the amount of lime in the blood, so that eggshells may be formed.

Several other organs are involved in the complex hormone relationships necessary to egg and sperm formation. The thyroid, for example, reaches maximum activity in February at about the time maximum body weight is attained. Maximum egg production follows a month or so later. The thyroid and egg production decline together during the summer. Research at the Missouri Experiment Station with iodine-containing proteins fed to laying hens indicates that these may supplement declining thyroid activity in the summer months and thus maintain a high rate of egg production. These proteins are not yet available for farm use.

Several chemicals have been found to act similarly to the female hormone. At the Oklahoma Experiment Station it was learned that certain of these chemicals, added to the feed for a few days, cause males, even old cocks, to assume characteristics of the capon, such as plump, soft flesh. We must postpone practical application of these results until we have removed the remotest possibility that the flesh of such treated birds, when eaten by men, will have a feminizing effect on them.

THE AUTHOR

Theodore C. Byerly is in charge of poultry investigations in the Bureau of Animal Industry. He is a graduate of the University of Iowa.