Plasma prolactin levels were measured in free-living breeding adult and immature pre-breeding macaroni Eudyptes chrysolophus and gentoo Pygoscelis papua penguins at Bird Island, South Georgia 54 degrees S, 38 degrees W. Macaroni and gentoo penguins first breed at and 2 years of age, respectively. This pattern is similar to that seen in other altricial species and is consistent with delayed onset of brood patch development and full incubation efficiency, which has been ly reported in penguins. Adult female macaroni penguins showed a marked, but transient, increase in prolactin concentrations within 24 hr of the first egg being laid from 1.
For each species and sex, half of the animals were either left untreated to serve as controls C or received ear implants females one and males two implants of melatonin MEL in May spring. Each C and MEL group of females was kept separately and away from males for 5 weeks after implantation and then, C and MEL males were ed with the respective groups for 45 sheep and 35 days goats.
Animals not conceiving during the early June—July breeding season, were mated again in September natural breeding season. The reproductive performance and the day milk yield of animals giving birth during the two seasons were compared.
For both species, most of the other characteristics examined were ificantly affected by season, but not by treatment. Females giving birth early in the season were approximately 80 days younger at parturition and recorded a lower body weight at mating than those giving birth in the natural February—March season.
In the first mating period, the animals mated and conceived had similar body weights to those not mated.
The natural, compared with the early June—July mating season, was associated in sheep with higher litter weight at birth 7. Total litter size at birth and day milk yield after weaning, were not ificantly different between the two seasons.
It could be concluded that melatonin implants administered during the last month of spring in autumn-born female Chios sheep and Damascus goats, advanced the initiation of their breeding season by about 80 days when ed with young males also treated with melatonin implants.
The overall reproductive performance and milk yield of animals breeding early, was satisfactory and comparable to that of animals breeding in the natural breeding season. View PDF. Access through your institution Purchase PDF. Author links open overlay panel C.
Papachristoforou A. Koumas C. Add to Mendeley Share. Keywords Melatonin.
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