Effect of photoperiod and quantitative feed restriction in a broiler strain on onset of lay in females and onset of semen production in males: A genetic hypothesis

The effects of feed restriction and photoperiod on body weight (WTSXM) and age (ASXM) at onset of mature semen production in males and onset of lay in females of a broiler female line were examined. Feeding treatments were as follows: ad libitum (AL) and quantitative feed restriction (QR). Photoperi od treatments were as follows: open shed (OS), in which the chicks were rea red under naturally increasing daylight with supplemental light; dark room (DR), in which chicks were reared under short days, gradually increasing fr om 6 h of light (L) to 11.5L; and dark room to open shed (DR-OS), in which chicks reared under short days in the dark room were transferred to the ope n shed at 149 d. Treatment effects were similar in direction in males and f emales, suggesting similar control of entry into reproduction of the two se xes, although within a given treatment, males matured earlier than females. Effects of feeding and photoperiod treatments were additive. Relative to Q R, the AL feeding treatment increased WTSXM by 832 g for males and 1,089 g for females; ASXM was decreased by 15.8 d for males and 9.3 d for females. Relative to OS, the DR photoperiod increased WTSXM by 391 g for males and 5 13 g for females; ASW was increased by 17.5 d for males and 26.8 d for fema les. The DR-OS photoperiod increased WTSXM by 86 and 169 g for males and fe males, respectively; ASXM was increased by 6.1 d and 4.9 d, respectively. U nder DR, the delay in onset of sexual maturity caused by QR was not due to failure to reach threshold body weight or age and, hence, appears to have r esulted from the feed restriction itself. A similar delay for QR was found under OS but might have been due to failure to reach threshold body weight. It is speculated that the delay in onset of sexual maturity caused by feed restriction may be an ecological adaptation or, alternatively, a result of nutritional imbalance.