title: Importance of estrus on pregnancy per insemination in suckled Bos indicus cows submitted to estradiol/progesterone-based timed insemination protocols.
abstract: The objective was to evaluate the effect of estrus occurrence (based on removal of tail-head marks) on ovarian responses and pregnancy per AI (P/AI; 30 d after AI) in suckled Bos indicus beef cows submitted to timed AI (TAI) protocols. Cows received an intravaginal device containing 1.0 g progesterone, and 2.0 mg estradiol benzoate im; 8 d later, the intravaginal device was removed, and they were given PGF(2α) (0.25 mg of cloprostenol sodium) and 300 IU of eCG, with TAI 48 to 52 h later. In Experiment 1, cows were assigned to receive one of three treatments: 1 mg of estradiol cypionate (ECP) im at progesterone (P4) device removal (N = 178); 10 μg of GnRH im at TAI (N = 190); or both treatments (N = 172). In cows given estradiol (ECP or ECP + GnRH), more displayed estrus (P = 0.002) and became pregnant (P < 0.0001) compared with those receiving only GnRH. In Experiment 2, the effect of the occurrence of estrus on ovarian responses was evaluated in cows (N = 53) synchronized using ECP at device removal. Cows that displayed estrus had a greater diameter of the largest follicle (LF) at device removal (P < 0.0001), a greater diameter at TAI (P < 0.0001), a greater ovulation rate (P = 0.02), a larger CL (P = 0.02), and a greater P4 concentration (P < 0.0001) than cows that did not display estrus. In Experiment 3, the effect of GnRH treatment on P/AI at TAI was evaluated in cows that received ECP at device removal, and either displayed, or did not display, estrus (N = 726). There was no estrus by GnRH interaction (P = 0.22); the P/AI was greater (P < 0.0001) in cows that displayed estrus (61.9%) than cows that did not display estrus (41.4%). However, GnRH did not improve (P = 0.81) P/AI (GnRH = 53.7% vs. no GnRH = 52.6%). In conclusion, exogenous estradiol at device removal increased both the proportion of suckled Bos indicus cows that displayed estrus and P/AI. Cows that displayed estrus had better ovarian responses (i.e., larger follicles at TAI, a greater ovulation rate, larger CL, and greater P4 concentrations) following an estradiol/P4-based synchronization protocol. Although occurrence of estrus improved pregnancy outcomes, GnRH at TAI did not improve P/AI in suckled Bos indicus cows treated with ECP, regardless of estrus occurrence.
authors.affiliation: Department of Animal Reproduction, FMVZ-USP, Sao Paulo, Brazil.
authors.forename: M F
authors.initials: MF
authors.lastname: Sá Filho
authors.forename: J E P
authors.initials: JE
authors.lastname: Santos
authors.forename: R M
authors.initials: RM
authors.lastname: Ferreira
authors.forename: J N S
authors.initials: JN
authors.lastname: Sales
authors.forename: P S
authors.initials: PS
authors.lastname: Baruselli
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology; D004971:Estrus / Q000502:physiology*; D005260:Female; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D006080:Ovarian Follicle / Q000000981:diagnostic imaging; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology; D014463:Ultrasonography
chemical_list: D011374:Progesterone; D004958:Estradiol