Change in the effect of constant photoperiods on the rate of sexual maturation in modern genotypes of domestic pullet

Abstract

1.	Data for modern egg-type hybrids reared on constant daylengths show that, as expected, they mature more quickly than earlier genotypes. However, the constant photoperiod which gives earliest sexual maturity has not changed as a result of selection and is 10 h for both early and modern genotypes.
2.	Further analysis showed that the rate of delay in sexual maturity for constant photoperiods above 10 h is similar for modern and for early hybrids (+0·29 d for each incremental one hour of photoperiod), the response of modern hybrids below 10 h (+4·22 d for each one-hour reduction in photoperiod) is more than double that of early hybrids (+1·71 d/h).