Abstract
Seasonal changes in peripheral plasma androgen levels in male goats were studied in 3 Saanen goats (seasonal breeders) and 3 Shiba goats (continuous breeders). Hourly blood sampling was carried out for 24 h in May (spring) and November (autumn) for measurement of plasma concentrations of testosterone and androstenedione. There were episodic bursts of secretion of androstenedione and testosterone during the 24 h periods in both May and November in both breeds. The mean levels of testosterone were 7.0-9.1 fold higher in November than those in May in the Saanen goat, whereas 1.2-2.9 fold higher in the Shiba goat. The degree of changes in the peak magnitude and the base-line level of testosterone in each individual in November were also somewhat smaller in the Shiba goat than in the Saanen goat. The plasma androstenedione levels in both breeds showed a similar change to testosterone, but the magnitude of fluctuation was only 1-10% of that in testosterone. These results suggest that the pattern of androgen release in male goats is episodic and follows marked seasonal changes, which are more conspicuous in Saanen breed.
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