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

Previous studies indicate that responsiveness to photoperiod (PR) has deter iorated in White Rock heavy breed females and males, and that selection for increased PR in females has a positive effect on egg production. Ln order to determine whether PII can be affected by selection in males, a two-way s election experiment for high and low PR, as expressed through early and lat e onset of mature semen production under suboptimal photoperiod, was implem ented 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 selecti on lines did not differ significantly in 6-wk body weight. Males of the hig h-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 < 0.0 1) 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 male s, with parallel effects on female PR and reproductive performance. This re sult carries the potential of improving reproductive performance of male an d female broiler chickens through mass selection for early sexual maturity among males.