| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1992: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1991: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
In Japanese quail, a change of photoperiods from long days to short days did not suppress circulating luteinizing hormone (LH) to nonbreeding levels, but the photoperiodic change with lowering ambient temperatures induced suppression of plasma levels of LH resulting in collapse of gonadal activity. This was accompanied with an increase in plasma levels of triiodothyronine, but thyroxine showed no major change.
Administration of triiodothyronine, but not thyroxine, suppressed plasma levels of LH to nearly nonbreeding levels in quail kept on short days. After removal of triiodothyronine implants, plasma levels of LH maintained the preceding low levels.
Male and female Japanese quail were kept in outdoor flying cage collectively. Blood sample were collected and reproductive behaviors were observed for full 2 years. Changes in plasma levels of gonadotropins and the behaviors indicated that the quail maintained reproductive activity from April to September. This term is relatively long compar
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ed to that of white-crowned sparrows which terminate reproduction in June to July due to photorefractriness. At the end of the breeding season when LH decreased, there were always increase in plasma levels of triiodothyronine.
Japanese quail we use come from a commercial breeders for eggs and meat and are possibly domesticated for their purposes. It is now very difficult to obtain wild population of Japanese quail. We fortunately obtained quail which were derived from wild populations and maintained as a closed colony from professor A.Nakamura of University of Shizuoka, Hamamatsu college. There were, however, no difference in responses to photoperiods and temperature between the wild-derived and commercial quail.
Short day treatment did not increase 5'-monodeiodinase activity of liver, but short days plus low temperature induced significant increases in the enzyme activity.
These results indicate that in Japanese quail low temperatures enhance 5'-monodeiodinase activity resulting in increases in plasma levels of triiodothyronine. Triiodothyronine thus suppress circulating LH and terminate reproductive activity in late summer to autumn. Less
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