Reproductive performance and progesterone secretion in estrus-induced Manchega ewes treated with hCG at the time of AI

Two experiments were conducted to determine the effects of supplementing hCG at insemination on the luteal function and reproductive performance in estrus-induced mature Manchega ewes. The first experiment was carried out under field conditions with 1560 ewes on 27 farms. After estrous synchronisation with progestagen sponges and eCG, cervical inseminations were performed between October and February (breeding season) on 665 ewes on 12 farms and between March and June (non-breeding season) on 895 ewes on 15 farms. In each period and within each farm, approximately half of the ewes received an i.m. injection of 500 IU hCG at the time of insemination. The other half remained untreated and served as controls. Neither fertility (hCG: 44.2%; control: 42.0%) nor prolificacy (hCG: 1.57; control: 1.54) were affected by hCG treatment. However, on farms where fertility in the control group was persistently low, fertility of the hCG treated ewes was increased by 7.6% relative to those not treated (P < 0.1). The second experiment was carried out on 64 ewes from an experimental flock. Estrus and ovulation were induced in all ewes as in experiment 1. Thirty-two ewes received a single i.m. injection of 500 IU hCG at the time of intrauterine insemination, while the other half were not treated. Plasma progesterone (P4) concentrations was measured every 2 days over a 28 day period following insemination. Progesterone secretion in the inseminated pregnant ewes was not modified by the hCG administration. However, a tendency (P < 0.1) for higher P4 concentrations from days 8 to 14 was observed in those ewes that had been treated with hCG, but that did not conceive at AI. Pregnancy (62.5% and 59.4%), fertility or number of ewes lambing/ewes inseminated (56.3% and 50.0%) and prolificacy (1.56 and 1.50) of the inseminated pregnant ewes did not differ between the hCG-treated and control ewes. In ewes that failed to conceive at AI and were mated at the next oestrus (return cycle), fertility was increased by 12.1% (P < 0.1) in those ewes that had previously been treated with hCG (58.3%), compared with those not treated (46.2%). Results indicate that hCG treatment did not improve reproductive performance in estrus-induced and AI’d Manchega ewes, but treatment may be beneficial in increasing fertility in ewes from farms with low fertility rates. © 2006 Elsevier B.V. All rights reserved.