Abstract: To study the regulation of photoperiod on seasonal reproduction and the associated endocrine mechanisms in Magang geese, adult breeding geese and ganders were exposed to natural photoperiod (controls), or subjected to an artificial program of long and short photoperiods (experimental birds).In both groups, egg laying ceased after photoperiod increased, and onset and continued when photoperiod decreased or remained for 11 h.Treatment with the artificial photoprogram also increased the eggs laid by 85.6%, from the 26.3 eggs per control goose to 48.8 eggs on average in the experimental goose.In both control and experimental ganders, plasma LH concentrations were high in reproduction season from August to March or under short photoperiod, but decreased to low levels in non-reproduction season from April to July or under long photoperiod.A similar but much less marked seasonal pattern of plasma LH concentrations was observed in geese.In all geese and ganders, seasonal patterns of PRL concentrations were opposite to those of LH, in relation to changes of photoperiod.Plasma testosterone concentrations in ganders followed the seasonal secretion pattern of LH throughout experimental period.In addition, plasma T3 concentrations in both control and experimental ganders fluctuated throughout the experiment, but by no means correlated to changes of photoperiod or season.These results demonstrated that long photoperiod directly inhibited while short photoperiod directly stimulated reproductive activities in Magang geese and ganders.The photoperiodic effect was mediated via the secretions of PRL and LH, whose seasonal secretions coordinated the reproductive seasonality of Magang geese.

Key words: Magang geese, seasonal reproduction, photoperiod, regulation