| Summary: | 碩士 === 東海大學 === 畜產與生物科技學系 === 96 === This study was conducted to discover the role of melatonin in the action pathway of photoperiod on the goose reproduction. Forty-five female and 21 male White Roman geese were randomly allotted into one of three groups. Geese in group A were exposed to natural photoperiod. Geese in groups B were exposed to long photoperiod (16L) from early March. Geese in group C were also exposed to 16L, but were fed 500 μg/bird/day at 15:30 from early March. Egg production was recorded every day. Semen samples were collected from ganders and evaluated at intervals of 4 weeks. Blood samples were collected from ganders at intervals of 2 weeks, and plasma testosterone levels were measured by RIA. The results showed that the date of egg production cease in group A (May 26) was significantly latter than that in group B (May 2) and C (April 28) (P < 0.05). The date of ending of laying was not significantly different between group B and C (P > 0.05). Sperm mortality rate and concentration in group A were significantly higher than those in group C in April, and higher than those in group B (P < 0.05) in October. In May, although ganders in group A could be collected semen, those in other 2 groups could not. All ganders could not be collected semen from June to September. All parameters of semen in all occasions were not different between groups B and C. Plasma testosterone levels gradually declined from the beginning of the experiment, and maintained at low levels until the next January when the plasma testosterone levels increased in group A. It is concluded that long photoperiod causes earlier cease of laying, and the effect can not be abolished by melatonin feeding. It is implied that melatonin is not the main mediator for the effect of photoperiod on reproduction in geese.
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