THE EFFECT AND AFTER-EFFECT OF VARIED EXPOSURE TO LIGHT ON CHICKEN DEVELOPMENT

¹ Poultry Husbandry Department, University of California, Davis, California

The present experiments were designed to determine the effects of:

a. Total daily amount of light

b. Intensity of light

c. Frequency of light intervals

on the growth and development of Leghorn chickens.

a. Total daily amount of light exposures: The first test dealt with the effect of supplementing natural light with continuous light. Continuous light improved body weight of all birds and testes size of males at 7 weeks, but impaired feather development. Continuous lighting delayed sexual maturity of pullets, and growth in both sexes was retarded until they reached 20 weeks of age.

In the second experiment under suboptimal light intensities, light exposure has no effect on body size after 12 weeks of age. Rate of sexual development was increased by larger daily exposures to light. These effects were more pronounced when treatments were applied to pullets over 90 days old than during earlier stages of development.

b. Intensity of light: Three light intensities were applied to growing birds: 0.0-0.4 foot-candles, 0.4-6.6 foot-candles, and 0.5-30.0 foot-candles. Growth was not affected by lower light intensities, but sexual maturity was delayed.

c. Frequency of light intervals: Body weight was unaffected by lighting frequency. Sexual maturity, however, was significantly advanced when suboptimal light exposure and light intensities were applied in frequent but small doses. Thus, it was found that 12 periods of 7.5 minutes of dim light per day produced a rate of sexual development almost equal to the rate with 14 hours per day of normal lighting. These results are taken as further proof that the after-effects of light on the reproductive mechanisms of chickens are considerable