Factors affecting reproductive response in anestrous crossbred cows treated with intravaginal progesterone or calf removal for 120 hours

Abstract

To study the effect of season (August-October, EP1; February- March, EP2), predominant breed (Bos taurus, BT; Bos indicus, BI), and number of parturitions (primiparous, PC; multiparous, MC) on reproductive response, 167 crossbred anestrous cows that were 90 to 130 d postpartum were allotted randomly to one of the following treatments: IP (n = 59), intravaginal sponge with 250 mg of medroxyprogesterone acetate (MAP) for 7 d; first day of treatment (Day 0), 50 mg MAP and 5 mg 17B-estradiol (17B-E) intramuscular (im); Day 5, 500 IU of eCG; 24 h after sponge removal (Day 8), 1.5 mg 17B-E im. CR (n = 57), temporary calf removal for 120 h. CG (n = 51), control group without treatment. Data were analyzed using Chi-square and GLM procedures. Season did not affect the reproductive response under the IP treatment; however, in EP2 cows under CR and/or CG had better reproductive response than in EP1: estrous rate (ER) was: CG: 36.8 vs 13.8%, respectively (P < 0.06), pregnancy rate at 30 d (TP30): CR: 40 vs 16.6%, (P < 0.02) and CG: 26.3 vs 3.4%, respectively (P < 0.06), pregnancy rate at 60 d (TP60): CR: 55 vs 23.3%, respectively (P < 0.02), interval parturition to 1st service (PFS): CG: 146.6 vs 181.8 d, respectively (P < 0.01), and interval parturition to conception (PCI): CR: 135.8 vs 156.7 d, (P < 0.05) and CG: 147.1 vs 171.1 d, respectively (P < 0.05). Predominant breed did not affect the reproductive response within any of the experimental group, except that under IP, BI cows had a greater TP60 than BI (62.5 vs 43.5%; P < 0.05). Primiparous cows under CR had lower ER than multiparous (39.5% vs 68.2%; P < 0.05); whereas in CG TP60 was 3.5 times lower in PC than in MC cows (7.7 vs 27.3%; P < 0.07). Also, in CG the PFS was shorter in MC than PC cows (153.8 vs 173.7 d; P < 0.05). Overall, the IP treatment followed by CR gave greater estrous rate, accumulated pregnancy at 30 and 60 d post-treatment and reestablished pregnancy in a shorter period after calving than the non-treatment control.