The effectiveness of Cosynch protocol in dairy heifers and multiparous cows

The aim of the present study was to evaluate the effects of Cosynch protocol on some reproductive parameters in Holstein multiparous cows (MC) (n = 54) and heifers (n = 53). Follicular development, presence of corpus luteum (CL) at different stages of Cosynch protocol, ovulation time and pregnancy rates were evaluated by ultrasonography in MCs and heifers. Pregnancy rates (PR) in MCs and heifers were found as 41% and 51% (P: 0.29, Z: -1.06). At the time of first Gonadotropinreleasing hormone (GnRH) (GnRH1), Prostaglandin F-2 alpha (PGF(2 alpha)) and final GnRH (GnRH2) injections, PRs in heifers and MCs which had CL on their ovaries were detected as 47.4%- 48.7% (P: 0.91, Z: 0.12), 60.5%- 48.7% (P: 0.30, Z: -1.4) and 62.1%- 36.4% (P: 0.031, Z: -2.15) respectively. Ovulations occurred in 24- 30 h interval after artificial insemination (AI) in MCs (50%) and heifers (35%) (P: 0.13, Z: 1.51). In conclusion, Cosynch protocol was found more effective and practical in heifers than MCs. In addition, ovulations that occurred before AI could be the reason of low conception rate for Ovsynch procedure in heifers.