Possible Strategies to Increase Ovulatory Follicle Size and Reduce Time to Ovulation in Lactating Dairy Cows

Specific objectives of this study were to examine growth response of the dominant follicle (DF) after administration of Folltropin-V (FSH and LH) at onset of luteolysis and investigate use of human chorionic gonadotropin (hCG) for decreasing ovulation time in lactating Holstein cows. On day 8 or 9 of a synchronized cycle, cows (n = 35) received an EAZI-BREED CIDR plus 100 μg of GnRH. CIDRs were removed 7 days later and cows were administered 500 μg cloprostenol. Concurrently, cows were randomly allocated to receive either 80 mg Folltropin-V (FSH, n = 19) or 4 mL of sterile saline (SAL, n = 16). Forty-nine hours later, cows that had received Folltropin-V or Saline were randomly subdivided to receive either 100 μg dose of GnRH or 3000 IU of hCG. Ultrasonography was performed to assess growth of the ovulatory follicle and confirm ovulation. Data were analyzed using the MIXED procedure of SAS. Size of the ovulatory follicle at time of GnRH/hCG administration was not different between Folltropin-V or Saline groups (17.1 ± 0.7 vs. 17.7 ± 0.6 mm, respectively; P = 0.521). Total growth of the ovulatory follicle from CIDR removal to GnRH/hCG administration did not differ between FSH (3.2 ± 0.6 mm) and Saline-treated cows (3.3 ± 0.4 mm; P = 0.891). When assessed from time of CIDR removal, ovulation occurred at a similar time for Folltropin-V (76.9 ± 0.7 h) and Saline-treated cows (78.0 ± 0.5 h; P = 0.196). When calculated from time of LH or hCG peak to ovulation, FSH-hCG cows presented the shortest time to ovulation (19.9 ± 0.4 h; P = 0.066). Whereas, from GnRH/hCG administration to ovulation, FSH-GnRH presented the earliest ovulation (25.0 ± 1.2 h; P = 0.013). In conclusion, Folltropin-V did not increase size of the ovulatory follicle at the time of GnRH/hCG administration. However, earlier ovulation occurred when combined with hCG as measured from time of gonadotropin peak. Conversely, when ovulation time is calculated from GnRH/hCG administration, FSH-GnRH produced the earliest ovulation.