Two-way selection for high and low responsiveness to photostimulation in broiler strain males.

Previous studies indicate that responsiveness to photoperiod (PR) has deteriorated in White Rock heavy breed females and males, and that selection for increased PR in females has a positive effect on egg production. In order to determine whether PR can be affected by selection in males, a two-way selection experiment for high and low PR, as expressed through early and late onset of mature semen production under suboptimal photoperiod, was implemented in White Rock heavy breed males. In each selection line, the selected males in each generation were mated to unselected females of the same line. After four generations of selection, males and females of the two selection lines did not differ significantly in 6-wk body weight. Males of the high-PR line, however, achieved mature semen production 18.9 d earlier (P < 0.01) and at a body weight 587 g lighter (P < 0.01) than the males of the low-PR line. Females of the high-PR line came into lay 25.9 d earlier (P < 0.01) and at a body weight 375 g lighter (P < 0.01) than females of the low-PR line; they also produced 13.9 more eggs over a 14-wk test period (P < 0.01). These results show that it is possible to affect PR by selection in males, with parallel effects on female PR and reproductive performance. This result carries the potential of improving reproductive performance of male and female broiler chickens through mass selection for early sexual maturity among males.