Effects of eCG and FSH in timed artificial insemination treatment regimens on estrous expression and pregnancy rates in primiparous and multiparous Bos indicus cows.

Effects were evaluated in Bos indicus cows of eCG and FSH on follicular growth, estrous expression, and pregnancy per artificial insemination (P/AI) as a result of fixed-time artificial insemination (TAI). In Experiment 1, extent of timing-of-ovulation synchronization among cows was evaluated after imposing an estrogen/progesterone-based treatment regimen. At progesterone device removal (D8), cows were administered: eCG, or FSH or served as untreated Controls. In Experiment 2, percentage of cows P/AI was evaluated when the Experiment 1-treatment regimen was imposed. On D10, all cows were artificially inseminated. In Experiment 3, cows were assigned to two treatment groups (Control and eCG) on D8 to evaluate percentage of cows P/AI and estrous expression. In Experiment 1, follicular dynamics were similar among treatment groups. In Experiment 2, follicular growth was greater (P = 0.0001) with the eCG treatment. There was an interaction of treatment × parity (P = 0.007) on percentage of cows P/AI. There was a greater percentage of primiparous cows P/AI in the eCG-treated than Control and FSH-treated cows. There was a greater percentage of eCG-treated multiparous cows pregnant as a result of TAI than Control cows. There was an interaction of treatment × parity (P = 0.005) on P/AI in Experiment 3, in which the eCG effect was more pronounced in primiparous cows. Treatment with FSH, therefore, was not as effective as eCG in stimulation of follicular growth or enhancing percentage of cows pregnant as a result of TAI. Physiological effects of eCG, however, were also more evident in primiparous cows.

Effect of induction of ovulation with estradiol benzoate at P4 device removal on ovulation rate and fertility in Bos indicus cows submitted to a TAI protocol.

This study aimed to minimize the number of times cattle need to be confined during protocols for TAI in beef cows treated for induction of ovulation with EB at the time of P4 device removal (P4r). In Experiment 1, cows were treated with P4 plus EB (Day 0; AM) and were allocated to one of three groups at P4r: EB8.5, EB at P4r on Day 8.5 (PM; three confinements); EB9, EB 24 h after P4r on Day 8 (AM; four confinements) and EC8, EC at P4r on Day 8 (AM; positive control; three confinements). At P4r, cows were treated with PGF2a plus eCG. Ultrasonography was performed from D8 to D12. The interval from P4r to ovulation was less in the EB8.5 compared to EB9 and EC8 group. There was no difference in the ovulation rate between groups. The variability of ovulation was greater in the EB8.5 and EC8 compared to EB9 group. In Experiment 2, cows of EC8 and EB9 groups were submitted to TAI 48 to 52 h (AM) or 54 to 58 h (PM) after P4r (D10). Cows of the EB8.5 group were submitted to TAI 38 to 42 h (AM) or 44 to 48 h (PM) after P4r (D10). There was no interaction between treatments and timing of AI and no treatment effect and timing of AI on P/AI. In conclusion, the delay compared to what typically occurs by 10 h of P4r concomitant with EB administration (Day 8.5) reduced the frequency of animal confinement for the TAI protocol without affecting the reproductive efficiency and the flexibility to perform the TAI in suckled beef cows.

Effects of eCG are more pronounced in primiparous than multiparous Bos indicus cows submitted to a timed artificial insemination protocol.

The effects of eCG on follicular growth, ovulation, and pregnancy per artificial insemination (P/AI) in multiparous and primiparous Bos indicus beef cows submitted to timed artificial insemination (TAI) were evaluated in three experiments. In experiments 1 (follicular responses; n = 64), 2 (follicular growth and ovulation rate; n = 662), and 3 (P/AI; n = 2092), cows submitted to TAI were assigned to receive one of two treatments on Day 8 of the synchronization protocol: control (no additional treatment) or eCG (300-IU of eCG intramuscularly). In experiment 1, largest follicle (LF) diameter on Day 8 (P = 0.56) and the interval from progesterone (P4)-device removal to ovulation (P = 0.79) did not differ between treatments. However, the maximum diameter of the LF (P = 0.05) and ovulation rate (P = 0.03) were greater in cows that received eCG. In experiment 2, the diameter of the LF on Day 10, follicular growth, and ovulation rate were greater in eCG-treated cows (P < 0.01). However, CL diameter was similar between treatments (P = 0.11). In experiment 3, there was a treatment-by-parity interaction (P = 0.003) on P/AI, such that treatment with eCG was more effective in primiparous cows. In conclusion, eCG treatment resulted in increased final follicular growth, ovulation rate, and fertility in B indicus cows submitted to TAI protocols, especially in primiparous cows.

Effect of circulating progesterone concentration during synchronization for fixed-time artificial insemination on ovulation and fertility in Bos indicus (Nelore) beef cows.

Four experiments were designed to evaluate the effect of different circulating progesterone (P4) concentrations during a synchronization of ovulation protocol for the timed artificial insemination (TAI) of Bos indicus (Nelore) beef cattle. In the first trial, 13 ovariectomized Nelore heifers were randomly allocated into one of three groups using new P4 devices (New; 1.0 g P4), previously used P4 devices for 8 days (Used1x), and previously used P4 devices for 16 days (Used2x), in a crossover experimental design. The circulating P4 concentrations during the P4 device treatment were lower for Used1x (2.3 ± 0.1 ng/mL) and Used2x (2.0 ± 0.1 ng/mL) than those for New (3.8 ± 0.2 ng/mL; P = 0.001). In the second trial, the ovarian follicular dynamics of 60 anestrous cows were evaluated after the cows received the treatments described previously (New [n = 20], Used1x [n = 20], and Used2x [n = 20]). During the insertion of the P4 device, the cows were administered 2.0-mg estradiol benzoate. Eight days later, the P4 device was removed, and the cows were administered 0.53-mg sodium cloprostenol, 300 IU eCG, and 1-mg estradiol cypionate. There were no differences among the groups during the interval from P4 device removal to ovulation (73.7 ± 2.9 vs. 69.8 ± 2.4 vs. 68.4 ± 2.3 hours) or regarding the ovulation rate (70.0% vs. 80.0% vs. 85.0%). However, the maximum diameter of the largest follicle was greater (P = 0.06) in the Used2x (15.3 ± 0.4 mm) than that of New (13.5 ± 0.8 mm) and Used1x (14.9 ± 0.5 mm). In experiment 3, 443 anestrous cows were randomly assigned into one of the three treatments (New [n = 144] vs. Used1x [n = 167] vs. Used2x [n = 132]) and received a TAI 48 hours after the P4 device removal. The diameter of the largest follicle during the device removal (10.7 ± 0.3 vs. 11.2 ± 0.2 vs. 11.3 ± 0.3 mm) and the 30-day pregnancy rates (51.4% vs. 53.9% vs. 43.2%) did not differ among the experimental groups. In experiment 4, a field trial with 593 B indicus (Nelore) cows was conducted to evaluate the pregnancy per AI using different levels of P4 in a TAI protocol (New [n = 189] vs. Used1x [n = 203] vs. Used2x [n = 201]). The pregnancy per AI was similar between the treatment groups (63.5% vs. 57.6% vs. 62.7%). In conclusion, the low circulating P4 concentrations that were released from a used P4 device efficiently controlled the ovarian follicular growth and exhibited no detrimental effects on the pregnancy rates of the B indicus (Nelore) beef cattle.