Gootwine, E., Institute of Animal Science, ARO, Volcani Center, Bet Dagan, 50-250, Israel
Bor, A., Institute of Animal Science, ARO, Volcani Center, Bet Dagan, 50-250, Israel
Shalhevet, D., Institute of Animal Science, ARO, Volcani Center, Bet Dagan, 50-250, Israel
Zenou, A., Institute of Animal Science, ARO, Volcani Center, Bet Dagan, 50-250, Israel
Braw-Tal, R., Institute of Animal Science, ARO, Volcani Center, Bet Dagan, 50-250, Israel

Pituitary response to exogenous gonadotrophin-releasing hormone (GnRH) was examined at a late stage of pregnancy in 10 Booroola-Assaf ewes heterozygous at the FecB locus (FecBFec+) and in11 Assaf ewes that were non-carriers (Fec+Fec+). Basal plasma luteinizing hormone (LH) and folliclestimulating hormone (FSH) concentrations were similar in the two genotypes. Administration of100 gg of GnRH resulted in a significant increase (P < 0-05) in plasma LH and FSH concentrationsin most of the ewes treated. Maximal responses were observed 105-135 min after GnRH treatment.Pituitary responses to GnRH were significantly lower (P <0-05) in Booroola-Assaf than in Assaf ewes.The decreased pituitary responsiveness observed in FecB gene carriers compared with Fec+Fec+ ewesmight be due to differences in the concentrations of ovarian or uterine hormones modulating therelease of gonadotrophin. The results suggest that FbcB-specific differences can be observed at thepituitary level. © 1992 CSIRO. All Rights Reserved.