Abstract
1. Oviposition times were recorded for broiler breeder hens under 8-, 10-, 11-, 12-, 13-, 14- and 16-h photoperiods. 2. Mean oviposition time (MOT) was delayed relative to dawn by approximately 0·5 h for each 1-h increase in photoperiod up to 14 h, but was similar for 14- and 16-h photoperiods. However, the 0·5 h/h regression for the time when half the eggs were laid continued through to 16 h. 3. The rate of change in MOT for each 1-h increase in ≤14-h photoperiod was similar to that reported for early and modern egg-type hybrids, but, compared with modern genotypes, time of lay itself was 1 h later than white-egg and 2·5 h later than brown-egg hybrids. 4. At photoperiods ≤12·25 h, the number of eggs laid before dawn increased by 4·5% for each 1-h reduction in daylength.
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