Strategies to improve fertility in Bos indicus postpubertal heifers and nonlactating cows submitted to fixed-time artificial insemination.

Two experiments were designed to evaluate strategies to increase fertility of Bos indicus postpubertal heifers and nonlactating cows submitted to a fixed-time artificial insemination (TAI) protocol consisting of an intravaginal device containing 1.9 g of progesterone (CIDR) insertion+estradiol benzoate on Day 0, CIDR withdrawal+estradiol cypionate on Day 9, and TAI on Day 11. In Experiment 1, heifers (n=1153) received a new or an 18-d previously used CIDR and, on Day 9, prostaglandin F(2 alpha) (PGF(2 alpha))+0, 200, or 300 IU equine chorionic gonadotropin (eCG). Heifers treated with a new CIDR had greater (least squares means+/-SEM) serum concentration of progesterone on Day 9 (3.06+/-0.09 ng/mL vs. 2.53+/-0.09 ng/mL; P<0.05) and a smaller follicle at TAI (11.61+/-0.11 mm vs. 12.05+/-0.12 mm; P<0.05). Heifers with smaller follicles at TAI had lesser serum progesterone concentrations on Day 18 and reduced rates of ovulation, conception, and pregnancy (P<0.05). Treatment with eCG improved (P<0.05) follicle diameter at TAI (11.50+/-0.10mm, 11.90+/-0.11 mm, and 12.00+/-0.10mm for 0, 100, and 200 IU, respectively), serum progesterone concentration on Day 18 (2.77+/-0.11 ng/mL, 3.81+/-0.11 ng/mL, and 4.87+/-0.11 ng/mL), and rates of ovulation (83.8%, 88.5%, and 94.3%) and pregnancy (41.3%, 47.0%, and 46.7%). In Experiment 2, nonlactating Nelore cows (n=702) received PGF(2 alpha) treatment on Days 7 or 9 and, on Day 9, 0 or 300 IU eCG. Cows receiving PGF(2 alpha) on Day 7 had lesser serum progesterone concentrations on Day 9 (3.05+/-0.21 ng/mL vs. 4.58+/-0.21 ng/mL; P<0.05), a larger follicle at TAI (11.54+/-0.21 mm vs. 10.84+/-0.21 mm; P<0.05), and improved (P<0.05) rates of ovulation (85.4% vs. 77.0%), conception (60.9% vs. 47.2%), and pregnancy (52.0% vs. 36.4%). Treatment with eCG improved (P<0.05) serum progesterone concentration on Day 18 (3.24+/-0.14 ng/mL vs. 4.55+/-0.14 ng/mL) and the rates of ovulation (72.4% vs. 90.0%) and pregnancy (37.5% vs. 50.8%). In conclusion, giving PGF(2 alpha) earlier in the protocol in nonlactating cows and eCG treatment in postpubertal heifers and nonlactating cows improved fertility in response to a TAI (progesterone+estradiol) protocol.