Efficacy of hCG and GnRH with Respect to Follicular Size and Presence of the Corpus Luteum in Cosynch Protocol Integrated with Norgestomet in Lactating Cows

Abstract

Efficacies of hCG and GnRH with respect to follicular diameter in Cosynch protocol were investigated. Lactating cows (n=119) received injections of GnRH and PGF 2 7 d apart. Norgestomet ear implant was inserted at GnRH administration and removed prior to PGF 2 injections. Presence of the corpus luteum (CL) at GnRH and PGF 2 injections, and diameter of preovulatory follicle [small (SPF) <8 mm or large (LPF) ≥8 mm] at PGF 2 were determined with transrectal ultrasonography (USG). The animals were randomly treated with GnRH (0.01 mg; GPG, n=62) or hCG (1,500 IU; GPH, n=57) at timed artificial insemination (TAI) 56 h after injection of PGF 2α . Pregnancies were diagnosed with USG 32-35 d after TAI. Pregnancies per TAI (P/TAI) were significantly (P<0.05) lower in GPH cows (28.1%; 16/57) compared to those in GPG animals (46.8%; 29/62). P/TAI with respect to follicular size did not differ between GPG and GPH cows, although P/TAI was numerically higher in LPF (30.0%; 15/50) than in SPF (14.3%; 1/7) in GPH cows. P/TAI in cows without CL at PGF 2 was 2.5 (1.0-6.7) times higher (P<0.01) in GPG (20.0%; 3/15) compared to GPH (10.5%; 2/19). In conclusion, use of hCG in milieu of the second GnRH in Cosynch+progesterone insert protocol did not have any advantage in lactating cows.

Comparison of conception rate following GnRH and hCG based synchronization protocols in functionally infertile cows

“…In the present study, CR in hCG based protocols was significantly (P<0.05) lower as compared to GnRH based treatments. Our results are in accordance with the findings of other workers (Keskin et al 2010, Pancarci et al 2013. Human chorionic gonadotropin has seen limited use in estrus synchronization protocols.…”

“…Geary et al (2001) also indicated a small reduction in CR when Cosynch is compared with Ovsynch, which is similar with our findings. In present study, 33.33% CR following hCG based modified Ovsynch treatment protocol (G3) was in concurrence with CR (28.10 and 37.60%) reported by Pancarci et al (2013) and Keskin et al (2010) respectively. In modified Co-synch protocol (G4), lower CR (16.67%) was recorded in our study as compared to 34% recorded by Geary et al (2001).…”