Effects of exogenous melatonin and photoperiod on sexual maturation in pullets.

Hy-Line Gray commercial pullets were maintained under 8-h photoperiods, 16-h photoperiods and 16-h photoperiods supplemented with a diet containing 20 or 200 mg/kg melatonin (MEL) to investigate the role of MEL in sexual development. A total of 256 Hy-Line Gray commercial pullets were placed, four birds to a cage, in four similar light-proof rooms (8-h photoperiod) at 6 weeks of age. At 70 day, three rooms containing a total of 192 birds were transferred to a 16-h photoperiod, whereas 64 birds were maintained under the 8-h photoperiod. Diets containing MEL at 20 and 200 mg/kg were fed to birds in two of the rooms under 16-h photoperiods. Birds maintained under an 8-h photoperiod matured 11.25 day later than those maintained under a 16-h photoperiod (p < 0.05). The group of birds receiving 20 mg/kg MEL matured 1.19 day later than those maintained under the 16-h photoperiod and 10.06 day earlier than those maintained under the 8-h photoperiod. The group of birds receiving 200 mg/kg MEL matured 3.13 day later than those maintained under a 16-h photoperiod and 8.12 day earlier than those maintained under an 8-h photoperiod. The average body weight of birds maintained under the 8-h photoperiod was greater than that of birds maintained under the 16-h photoperiod (p < 0.05) and was similar between the different MEL groups. The abdominal fat weight was lower in 16L:8D group compared with 8L:16D group (p < 0.05). The concentrations of follicle-stimulating hormone, luteinizing hormone, oestrogen and insulin did not differ significantly among the groups. The melatonin concentration in 200 mg/kg melatonin group was higher than that observed in the other groups; however, this concentration did not differ significantly (p > 0.05). These data suggest that the birds did not perceive the final 8-h photoperiod as being part of the night when they were given the MEL diets; continuously high plasma MEL was not observed in birds that responded as if they were in constant darkness. However, the later maturity of the groups administered MEL diets compared with the groups maintained under a constant 16-h photoperiod clearly indicated that MEL has some influence on the sexual maturity of pullets.

Effects of photoperiod on ovarian morphology and carcass traits at sexual maturity in pullets.

This paper is concerned with the effects of photoperiod on ovarian morphology and carcass traits at sexual maturity in egg-type hens. Two hundred fifty-six commercial egg-type pullets were initially subjected to a photoperiod of 23L:1D, which was reduced to 22L:2D at 1 wk, to 18L:6D at 2 wk, and to 16L:8D at 3 wk. From 4 to 20 wk, the photoperiod was 8L:16D. At 20 wk, 32 pullets were individually caged in individually lit cages, with 8 cages per unit. Two cage units were placed into 4 photoperiods of 17L:7D, 15L:9D, 13L:11D, and 11L:13D, respectively. Each bird was processed when it reached sexual maturity (SM), and carcass and ovarian morphology were assessed. The results showed that photoperiod had an effect on the timing of SM, and the age at first egg was 5.7 d earlier for hens exposed to the 17L:7D photoperiod than the 11L:13D photoperiod. However, photoperiod had no effect on BW at SM. A photoperiod of 11L:13D limited ovarian follicle formation and increased carcass protein and lipid compared with birds on longer photoperiods, whereas the 17L:7D photoperiod restricted ovary and oviduct full development. These results indicated that excessively long and short photoperiods can restrict reproductive development in egg-type hens.