1921
The Effects of Gonadotropic Stimulation on Fertility of Progesterone-treated Nulliparous Ewes Bred During Seasonal Anestrous
The Effects of Gonadotropic Stimulation on Fertility of Progesterone-treated Nulliparous Ewes Bred During Seasonal Anestrous.
A.K. Redhead*, K.N. D’Souza, S.L. Rastle-Simpson, Q.S. Baptiste and M. Knights
Division of Animal and Nutritional Sciences, West Virginia University, Morgantown, WV
Attempts to breed fall born ewe lambs and yearlings (nulliparous females) during seasonal anestrus have resulted in limited success. Low fertility in these nulliparous females may be related to a deficiency of ram induced gonadotropic release necessary to stimulate sufficient estrogen production to induce estrus. The objective of this study was to evaluate the effects of gonadotropic stimulation on fertility in nulliparous females bred out of season. Nulliparous females (N = 311) from 5 farms throughout WV and PA received progesterone using CIDR inserts (0.38g progesterone) for 5 days prior to ram introduction between the months of April and July. At insert removal, females at each farm were randomly assigned to receive a single injection of gonadotropin containing 240 IU eCG and 120 IU hCG (GS: 3mL P.G. 600, Intervet, i.m) or to receive no further treatment (C). Pregnancy diagnosis was conducted using transrectal ultrasonography between days 25-30 post ram introduction, at which time rams were removed, and a second pregnancy diagnosis was conducted 20-30 days later. Analysis of variance was conducted using the GLM procedures of SAS to evaluate the effects of gonadotropic stimulation, farm and their interaction, and the least square means were computed for reproductive performance variables. Gonadotropin treated females had higher estrous response (P = 0.002, 72% ± 3.7 vs. 51% ± 4.0), conception rate (P=0.0562, 68.3% ± 6.0 vs. 44.5% ± 11), pregnancy to the first service (P=0.003, 66% ± 4.2 vs. 37% ± 4.4), proportion of females lambing to the first service period (P = 0.0051, 54.5% ± 4.4% vs. 34% ± 4.4%), proportion of females lambing (P = 0.0013, 54% ± 4.4 vs. 34% ± 4.4) and lambing rate (P = 0.0018, 77.6% ± 7.0 vs. 45.1% ± 7.0) than C females. The results of the current study indicate that inadequate gonadotropin stimulation or estrogen production might be limiting fertility in nulliparous ewes bred during seasonal anestrus. Further, supplementation with the gonadotropin combination, P.G. 600 at progesterone withdrawal significantly increased fertility of progesterone-primed nulliparous females when bred outside their normal breeding season.
Keywords: Out of season, Ewe Lambs, Yearlings, Fertility, P.G. 600, Gonadotropic stimulation