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Effect of stimulation with a gonadotropin mixture on reproductive outcome in nulliparous ewes bred during seasonal anestrus and early breeding season
- Knights, Marlon, Redhead, Adam, D'Souza, Kellie, Baptiste, Quinn
- Animal reproduction science 2015 v.159 pp. 198-204
- Texel, anestrus, breeding, breeding season, equine chorionic gonadotropin, ewes, human chorionic gonadotropin, lambing, lambing rate, lambs, pregnancy rate, progesterone, rams, reproductive performance, yearlings
- To evaluate the effect of gonadotropic stimulation on the reproductive response of nulliparous acyclic female sheep during mid-anestrous and early breeding season, fall-born ewe lambs of mixed breeding (N=191; ∼7 months old; study 1) and yearlings (Dorset X Texel (DT), N=120, study 2) were assigned randomly during May to July to be either pre-treated with progesterone using CIDR-g (0.3g of progesterone) devices for 5 days or to also receive gonadotropins (240IU eCG and 120IU hCG, 3mL i.m. injection of P.G. 600®) at CIDR-g removal. Study 3 was conducted with nulliparous acyclic DT yearling ewes (N=104) in late August and was similar to study 2 except that a group of control ewes that were not treated was included. Gonadotropic stimulation increased estrous response (P=0.0002), pregnancy rate to the first service period (P=0.0007), proportion of ewes lambing (P=0.03) and the lambing rate (P=0.01) in fall-born ewe lambs (study 1), but did not modify reproductive outcome in yearling females (study 2) during mid-anestrus. During the transition into the breeding season (study 3), progesterone pre-treatment increased the pregnancy rate and the proportion of ewes lambing to first service after ram introduction (P=0.003 and P=0.02, respectively). However, gonadotropic stimulation of progesterone pre-treated yearlings did not modify reproductive performance variables. In conclusion, gonadotropic stimulation improved reproductive outcome in fall-born ewe lambs bred during the mid-anestrous period, but did not affect reproductive outcome in yearling females.