Importance of estrus on pregnancy per insemination in suckled Bos indicus cows submitted to estradiol/progesterone-based timed insemination protocols

• Published in: Theriogenology Vol. 76; no. 3; pp. 455 - 463
• Main Authors: Sá Filho, M.F, Santos, J.E.P, Ferreira, R.M, Sales, J.N.S, Baruselli, P.S
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.08.2011; [Oxford]: Butterworth-Heinemann; [New York]: Elsevier Science
• Subjects: administration & dosage; animal ovaries; Animals; beef cows; blood; Cattle; Cattle - physiology; equine chorionic gonadotropin; estradiol; Estradiol - administration & dosage; Estradiol - pharmacology; Estradiol cypionate; Estrus; Estrus - physiology; Female; GnRH; gonadotropin-releasing hormone; insemination; Insemination, Artificial; Insemination, Artificial - methods; Insemination, Artificial - veterinary; methods; Nelore; Ovarian Follicle; Ovarian Follicle - diagnostic imaging; ovulation; pharmacology; physiology; Pregnancy; pregnancy outcome; Pregnancy Rate; progesterone; Progesterone - administration & dosage; Progesterone - blood; Progesterone - pharmacology; Reproduction; sodium; Ultrasonography; veterinary; zebu; Nelore; Reproduction; Estradiol cypionate; Estrus; GnRH
• ISSN: 0093-691X; 1879-3231; 1879-3231
• DOI: 10.1016/j.theriogenology.2011.02.022

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 PGF₂α (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.