title: Effect of stimulation with a gonadotropin mixture on reproductive outcome in nulliparous ewes bred during seasonal anestrus and early breeding season.
abstract: 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.
authors.affiliation: Division of Animal and Nutritional Sciences, West Virginia University, PO Box 6108, Morgantown, WV 26506-6108, United States. Electronic address: marlon.knights@mail.wvu.edu.
authors.forename: Marlon
authors.initials: M
authors.lastname: Knights
authors.affiliation: Division of Animal and Nutritional Sciences, West Virginia University, PO Box 6108, Morgantown, WV 26506-6108, United States.
authors.forename: Adam
authors.initials: A
authors.lastname: Redhead
authors.affiliation: Division of Animal and Nutritional Sciences, West Virginia University, PO Box 6108, Morgantown, WV 26506-6108, United States. Electronic address: kdsouza87@gmail.com.
authors.forename: Kellie
authors.initials: K
authors.lastname: D'Souza
authors.affiliation: Division of Animal and Nutritional Sciences, West Virginia University, PO Box 6108, Morgantown, WV 26506-6108, United States. Electronic address: Quinn_Baptiste@berea.edu.
authors.forename: Quinn
authors.initials: Q
authors.lastname: Baptiste
mesh_terms: D000780:Anestrus / Q000187:drug effects*; D000822:Animal Husbandry / Q000379:methods; D000818:Animals; D005260:Female; D006062:Gonadotropins / Q000494:pharmacology*; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology / Q000662:veterinary*; D011270:Pregnancy, Animal / Q000187:drug effects*; D011374:Progesterone / Q000494:pharmacology; D012621:Seasons; D012756:Sheep
chemical_list: D006062:Gonadotropins; D011374:Progesterone
keywords: Anestrus; Ewe lambs; Gonadotropin; Reproduction