Increase in Ovulation Rate in Sheep Following Administration of an LHRH Analogue

Abstract

A nonapeptide (D-Ser (TBU)6-EA10; Hoe 766; 25 times more potent than LHRH [luteinizing hormone releasing hormone] in LH [luteinizing hormone] and FSH [follicle stimulating hormone] releasing activity, was administered (2 .mu.g s.c. in 0.5% gelatin to ewes on day 1 (n = 51), day 12.5 (n = 48) or day 14.5 (n = 39) of the estrous cycle (day 0 = day of estrus. A control group (n = 23) was not treated. Ovulation rate at the estrus or time of expected estrus following treatment was increased (P < 0.05) in ewes injected on day 12.5 (1.36) compared to ewes in the control group (1.09) and ewes injected on day 1 (1.13), but not in ewes (0.05 < P < 0.10) injected on day 14.5 (1.29). Less ewes expressed estrus following treatment with Hoe 766 on day 14.5 (35%) than on day 12.5 (64%) or than on day 1 (90%), control group (82%). Hoe 766 may be a useful agent to increase ovulation rates in sheep and support the concept that gonadotropin concentrations in peripheral plasma on day 12-14 of the ovine estrous cycle may be important in determining ovulation rate at the subsequent estrus.