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Estradiol and MGA for estrus synchronization in cattle
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Theriogenology ESTRADIOL AND MGA FOR ESTRUS SYNCHRONIZATION
IN CATTLE
J.P. Kastelic’, D.H. McCartney*, A. Garci3, W. 01son4, and R.J. Mapletoft3 ‘Research Centre and 4Animal Diseases Research Institute, Lethbridge, AB; ‘Research Centre, Melfort, SK; and 3University of Saskatchewan, Saskatoon, SK
The objective was to evaluate the use of estradiol in estrus synchronization programs for beef cattle involving melengestrol acetate (MGA). In Experiment 1, all cattle were fed 0.5 mg/head/day MGA (MGA 100, The Upjohn Company, Orangeville, ON) for 7 d (designated Days 1 to 7) and given prostaglandin F,, (Lutalyse, The Upjohn Company) or cloprostenol (Estrumate, Coopers Agropharm Inc., Ajax, ON) on Day 7 to induce luteal regression. Half of the cattle were given 5 mg estradiol valerate (EV; Sigma Chemical Co., St. Louis, MO) dissolved in sesame oil and injected im on Day 1. At Location 1, a higher proportion (P c 0.005) of EV-treated heifers were detected in estrus and bred by artificial insemination (AI) on Days 8 to 14 compared to control heifers not receiving EV (27 of 33 versus 15 of 32), but there was no significant difference in the number pregnant 35 d after AI (12 versus 10). There were 83 of 104 EV-treated and 89 of 106 control cows bred by AI; 50 and 45, respectively, were diagnosed pregnant 35 d later (ns). Heifers bred by AI and all cows were exposed to bulls on Days 20 to 60. In the fall, 20 and 13 EV-treated and control heifers, respectively, were pregnant as were 92 and 96 cows (ns). At Location 2, cattle were similarly treated and exposed to bulls on Days 8 to 50. Fall pregnancy rate was higher (P <0.015) for EV-treated than control heifers (44 of 48 versus 33 of 46) but differences were not significant for cows (22 of 26 versus 19 of 23). In Experiment 2, treatments were similar for 131 heifers and 213 cows, except that instead of EV, 5 mg estradiol 170 (E17/3; Sigma Chemical) and 100 mg progesterone (Sigma Chemical) were injected im on Day 1. In a third group, designated the PGF group, cattle were bred for 7 d and cloprostenol was given on Day 7 to those not yet bred. The interval from cloprostenol to AI was 4.4k1.8, 3.1kl.O and 1.9+1.0 d for 28 heifers bred by AI in the PGF, MGA and E17/3+MGA groups (ns) and was 2.4+0.2, 3.0+0.2 and 3.3+0.2 d for 78 cows (interval significantly shorter for cows in PGF group compared to other two groups). For cows, the percentage pregnant (approximately 40 d after breeding) to a synchronized estrus was greater in the PGF group (72%) than in the group treated with MGA (49%; P=O.OOS) and in the group receiving E17/3+MGA (54%; P
Theriogenology ESTRADIOL AND MGA FOR ESTRUS SYNCHRONIZATION
IN CATTLE
J.P. Kastelic’, D.H. McCartney*, A. Garci3, W. 01son4, and R.J. Mapletoft3 ‘Research Centre and 4Animal Diseases Research Institute, Lethbridge, AB; ‘Research Centre, Melfort, SK; and 3University of Saskatchewan, Saskatoon, SK
The objective was to evaluate the use of estradiol in estrus synchronization programs for beef cattle involving melengestrol acetate (MGA). In Experiment 1, all cattle were fed 0.5 mg/head/day MGA (MGA 100, The Upjohn Company, Orangeville, ON) for 7 d (designated Days 1 to 7) and given prostaglandin F,, (Lutalyse, The Upjohn Company) or cloprostenol (Estrumate, Coopers Agropharm Inc., Ajax, ON) on Day 7 to induce luteal regression. Half of the cattle were given 5 mg estradiol valerate (EV; Sigma Chemical Co., St. Louis, MO) dissolved in sesame oil and injected im on Day 1. At Location 1, a higher proportion (P c 0.005) of EV-treated heifers were detected in estrus and bred by artificial insemination (AI) on Days 8 to 14 compared to control heifers not receiving EV (27 of 33 versus 15 of 32), but there was no significant difference in the number pregnant 35 d after AI (12 versus 10). There were 83 of 104 EV-treated and 89 of 106 control cows bred by AI; 50 and 45, respectively, were diagnosed pregnant 35 d later (ns). Heifers bred by AI and all cows were exposed to bulls on Days 20 to 60. In the fall, 20 and 13 EV-treated and control heifers, respectively, were pregnant as were 92 and 96 cows (ns). At Location 2, cattle were similarly treated and exposed to bulls on Days 8 to 50. Fall pregnancy rate was higher (P <0.015) for EV-treated than control heifers (44 of 48 versus 33 of 46) but differences were not significant for cows (22 of 26 versus 19 of 23). In Experiment 2, treatments were similar for 131 heifers and 213 cows, except that instead of EV, 5 mg estradiol 170 (E17/3; Sigma Chemical) and 100 mg progesterone (Sigma Chemical) were injected im on Day 1. In a third group, designated the PGF group, cattle were bred for 7 d and cloprostenol was given on Day 7 to those not yet bred. The interval from cloprostenol to AI was 4.4k1.8, 3.1kl.O and 1.9+1.0 d for 28 heifers bred by AI in the PGF, MGA and E17/3+MGA groups (ns) and was 2.4+0.2, 3.0+0.2 and 3.3+0.2 d for 78 cows (interval significantly shorter for cows in PGF group compared to other two groups). For cows, the percentage pregnant (approximately 40 d after breeding) to a synchronized estrus was greater in the PGF group (72%) than in the group treated with MGA (49%; P=O.OOS) and in the group receiving E17/3+MGA (54%; P