Seasonal variation in LH and testosterone release in rams of two breeds.

Blood was collected hourly for 24 h in December, February, April, June and September from Préalpes du sud and Ile-de-France rams. Coincidence of the LH and testosterone peaks was found for 96.4% of a total of 670 LH peaks and 647 testosterone peaks. The number of LH and testosterone peaks increased by 66% in Ile-de-France rams and 200% in Préalpes du Sud rams between December and June (P less than 0.001). Values in June and September were similar in Préalpes du Sud rams. There were no differences between breeds in December, but in June, Préalpes du Sud had significantly more peaks than did Ile-de-France rams (P less than 0.025). The numbers of LH and testosterone peaks increased significantly (P less than 0.05) in Préalpes du Sud rams between December and February or April. These results indicate that, although numbers of peaks of LH and testosterone increase when the animals pass from the non-breeding to the breeding season, the genotype influences the pattern of release through the year.