Abstract
The objectives were to determine whether rates of conception, ovulation, presynchronization, or follicle and CL characteristics were altered after modifying the Double-Ovsynch (DO) protocol to include hCG compared with the DO protocol. Primiparous and multiparous lactating dairy cows (N = 183), and nulliparous dairy heifers (N = 51) were used. Cows were blocked by parity and heifers were stratified by age and breed before being randomly assigned to one of two treatments. All females received either 100 μg GnRH or 2000 IU hCG im, at initiation of the Pre-Ovsynch (PO) portion of the DO protocol (PO: GnRH/hCG, 7 days PGF2α and 3 days GnRH). After 7 days, females started the Breeding-Ovsynch portion of the DO protocol (Breeding-Ovsynch: GnRH, 7 days, PGF2α, 48 or 56 h and GnRH 16 hours timed artificial insemination with sex-sorted semen). Transrectal ultrasonography and blood samples were used to assess ovarian structures, ovulation, pregnancy diagnosis, and concentration of progesterone in plasma. Conception rates were similar in females treated with GnRH or hCG in cows (32.2 and 25.0%) and in heifers (30.8 and 36.0%). Ovulation rates in cows at the onset of PO were increased with hCG compared to GnRH (77.2 vs. 62.2%, P < 0.05). Concentrations of progesterone 7 days post-hCG or GnRH were greater in cows treated with hCG compared with GnRH (least significant mean ± SEM; 4.3 ± 0.3 and 3.0 ± 0.3 ng/mL, P < 0.01), but did not differ in heifers (4.5 ± 0.9 and 2.9 ± 0.9 ng/mL). More cows ovulated within 7 days post-hCG and a greater proportion of these cows tended to have failed luteal regression by Day 3 post-PGF2α compared with cows that had ovulated to GnRH (29.6 vs. 16.1%, P ≤ 0.10). The overall percentage of females which were synchronized to PO did not differ between GnRH- or hCG-treated cows (61.5% and 52.2%) and heifers (42.3% and 40.0%). In conclusion, no overall improvement in fertility was achieved by replacing the first injection of GnRH in the DO protocol with hCG.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
