Change in the effect of constant photoperiods on the rate of sexual maturation in modern genotypes of domestic pullet.
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).
Lewis
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PD
Animal and Poultry Science, University of KwaZulu-Natal, Pietermaritzburg, South Africa. peter.lewis@dsl.pipex.com
Morris
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TR
D000822:Animal Husbandry; D000818:Animals; D002645:Chickens / Q000235:genetics* / Q000502:physiology*; D005260:Female; D005838:Genotype; D017440:Photoperiod; D012189:Retrospective Studies; D012741:Sexual Maturation / Q000502:physiology / Q000528:radiation effects*; D013997:Time Factors