Endocrine regulations of reproductive seasonality, follicular development and incubation in Magang geese.

This study investigated the regulatory mechanisms of seasonal breeding, developments of ovarian follicles and incubation in Magang geese, a short day breeding bird. Throughout the year, plasma PRL concentrations increased in non-breeding season in spring and summer (from April to early August), and remained low in the rest of the year, while LH concentrations peaked in August and September and remained low in non-breeding season (March to June). Lengthening photoperiod increased PRL and decreased LH secretions, which inhibited follicular development, terminated lay and induced moulting, while shortening photoperiod decreased PRL and increased LH secretion and reinitiated lay. Long photoperiod stimulated PRL secretion occurred with increased gene expressions of PRL in the pituitary gland and VIP in the hypothalamus, but inhibition of LH secretion was without decreases in gene expressions of LH beta subunit and GnRH. Under breeding conditions, terminating incubation decreased PRL but increased LH concentrations and resumed lay in 24 days following recruitment of about 10 large white follicles into hierarchical development. Plasma concentrations of progesterone and inhibin peaked at peak lay, whereas LH concentrations exhibited a bi-phasic pattern with troughs at peak lay and incubation when PRL concentrations were high. Ninety percent geese exhibited incubation behaviour after laying one clutch of approximately eight eggs in approximately 30 days. In conclusion the seasonal reproductive activities in Magang geese is directly inhibited by long photoperiod and directly stimulated by short photoperiod via PRL and LH secretions, whose interplays also cause occurrences of four to five lay and incubation cycles in the breeding season.