EARLY GROWTH RATES OF CHICKENS WITH SPECIAL REFERENCE TO ULTRA-VIOLET LIGHT

Abstract

Early growth rates in excess of those reported as "normal" may be obtained. Chicks hatched in the early part of the season grow more rapidly than those hatched later. Chicks from hens 2 yrs. old and upwards are heavier at 30 days than those from hens 1 yr. old. Non-irradiated chicks penned with irradiated ones reacted as when penned separately. Forced feeding non-irradiated chicks with droppings of irradiated ones as a further test of the presence of a growth-promoting substance in the excreta was ineffective. Irradiating the dry mash for 10 minutes appeared to favor growth, but did not wholly prevent leg weakness. Sunning the food for half an hour did not favor growth. The addition of semi-solid buttermilk to the basic ration was very effective in promoting growth. Daily exposures of 5 and 15 sec. to the mercury vapor lamp were ineffective; 30 sec. were not completely adequate but 1 minute gave as good results as exposures up to 3 hrs. There were slight indications that prolonged or very intense radiations from the mercury vapor lamp retarded growth. Radiations for 1 and 10 min., twice weekly, at 3 ft. gave normal growth; less frequent radiations were inadequate. The natural covering of chicks is not penetrated by effective wave lengths of ultra-violet light; the usual receptive areas are those parts normally exposed. Effective ultra-violet light under some conditions penetrates muslin or celo-glass. Winter sunlight both promotes growth and prevents leg weakness.