title: Improved fertility in suckled beef cows ovulating large follicles or supplemented with long-acting progesterone after timed-AI.
abstract: We aimed to evaluate the effects and the interaction of size of the preovulatory follicle (POF) and long-acting progesterone (P4) supplementation after timed-AI on CL function and pregnancy success in beef cows. In experiment 1, ovulations of beef cows were synchronized starting on Day -10, and cows were split to receive sodium cloprostenol (large follicle group; LF; n = 31) or nothing (small follicle group; SF; n = 35). Ovulations were induced on Day 0, and cows were inseminated. Ovulated cows were assigned to receive placebo (LF/control group, n = 14; and SF/control group, n = 9) or 150 mg of long-acting P4 on Day 4.5 (LF/P4 group, n = 13; and SF/P4 group, n = 12). Diameter of POF, blood flow in POF wall, ovulation rate, and size and vascularization of CL were greater (P < 0.05) in LF group. In experiments 2 (unknown cyclic status) and 4 (noncycling), ovulations were synchronized, and beef cows received placebo or 150 mg of long-acting P4 on Day 4 after timed-artificial insemination. In experiment 2, pregnancy/AI (P/AI) did not differ (P > 0.1) between P4-treated (53.2%; 209/393) and control cows (56.2%; 219/390), but P/AI was greater in cows with a CL < 0.9 cm(2) on Day 4 that were P4-treated (57.9%, 22/38) versus placebo-treated (40.4%, 21/52; P < 0.05). In Experiment 4, P/AI was greater (P < 0.05) in P4-treated cows (55.6%, 105/189 vs. 46.0%, 86/187). In Experiment 3, cyclic-suckled beef cows were treated as described in Experiment 1 to generate animals with small (SF; n = 111) or large POF (LF; n = 109), and subdivided to receive placebo or P4 on Day 4. POF size, ovulation rate, CL area, and P/AI were greater (P < 0.007) in the LF group. Pregnancy/AI in ovulated cows were lower (P = 0.05) in the SF/control group (41.5%, 17/41) compared to LF/control group (62%, 31/50) and were similar for the SF/P4 group (55.6%, 25/45) and LF/P4 group (57%, 28/49) compared to others. In summary, smaller and less vascularized POF results in less functional CL and reduces ovulatory rate and P/AI in cyclic beef cows; the long-acting P4 injection on Day 4 after timed-artificial insemination may attenuate the negative effects of small POF/CL; and postovulatory P4 supplementation improved fertility in anestrous beef cattle.
authors.affiliation: Department of Animal Reproduction, School of Veterinary Medicine and Animal Science, University of São Paulo, Pirassununga, São Paulo, Brazil. Electronic address: gpugliesi@usp.br.
authors.forename: G
authors.initials: G
authors.lastname: Pugliesi
authors.affiliation: Department of Animal Reproduction, School of Veterinary Medicine and Animal Science, University of São Paulo, Pirassununga, São Paulo, Brazil.
authors.forename: F B
authors.initials: FB
authors.lastname: Santos
authors.affiliation: Department of Animal Reproduction, School of Veterinary Medicine and Animal Science, University of São Paulo, Pirassununga, São Paulo, Brazil.
authors.forename: E
authors.initials: E
authors.lastname: Lopes
authors.affiliation: Brazilian Agricultural Research Corporation, EMBRAPA Pantanal-CPAP, Corumbá, Mississippi, Brazil.
authors.forename: É
authors.initials: É
authors.lastname: Nogueira
authors.affiliation: Ouro Fino Saúde Animal, Ribeirão Preto, São Paulo, Brazil.
authors.forename: J R G
authors.initials: JR
authors.lastname: Maio
authors.affiliation: Department of Animal Reproduction, School of Veterinary Medicine and Animal Science, University of São Paulo, Pirassununga, São Paulo, Brazil.
authors.forename: M
authors.initials: M
authors.lastname: Binelli
mesh_terms: D000818:Animals; D000833:Animals, Suckling; D002417:Cattle; D048429:Cell Size; D030762:Estrous Cycle / Q000502:physiology; D004973:Estrus Synchronization / Q000379:methods; D005260:Female; D005298:Fertility / Q000187:drug effects*; D005300:Fertility Agents, Female / Q000008:administration & dosage; D007315:Insemination, Artificial / Q000662:veterinary*; D007774:Lactation / Q000502:physiology; D006080:Ovarian Follicle / Q000502:physiology*; D010060:Ovulation / Q000502:physiology*; D011247:Pregnancy; D011374:Progesterone / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D005300:Fertility Agents, Female; D011374:Progesterone
keywords: Anestrous; CL; Embryo; Estrous cycle; Uterus