Seasonal variations of pituitary and testis responsiveness to LHRH and HCG challenge respectively in rams of the East Friesian breed

A study was conducted to compare the variation in pituitary and testies responsiveness to an exogenous LHRH and HCG challenge, respectively, during the four season on total LH response to LHRH challenge. The greatest responses were observed during spring and summer (49.13+-4.00 and 43.40+-2.92 ng/ml.180 min, respectively, mean+-SEM) and the lowest during autumn and winter (33.47+-4.00 and 33.13+-3.13 ng/ml.180 min, respectively, mean+-SEM). When the total response was analysed by diving the area under the LH curve in two successive parts (0-90 min) and (90-180 min after the LHRH injection) a statistical significant difference (p0.005) for the values of the first part was observed between spring-autumn, spring-winter and also between spring-summer (p0.05). A statistical significant difference (p0.05) for the values of the second part of the curve was observed between spring-winter, spring-autumn and also between winter-summer (p0.005). The pattern of the LH response in summer is peculiar (breeding season-like response) for the first part of the curve and (anoestrus-like response) for the second part of the curve. As concerns the responsiveness of the testes there was a significant (p0.05) effect of season on testosterone levels after HCG treatment, with the highest response occurring in winter and the lowest in autumn (winter: 15.98+-0.49, spring: 12.81+-0.65, summer: 12.84+-1.11 and autumn: 8.86+-1.10 ng/ml, mean+-SEM). Taken together these data show that for that particular breed winter and autumn is the breeding season and the spring is the anoestrous season. Summer seems to be the transitional period, since the first part of the LH response curve resembles the pattern occurring in the breeding season, while the second resembles the pattern occurring in the anoestrous period. These summer differences could potentially be used to select rams within a breed for precocity (second part response resembling that of the breeding season).