Lecirelin-cloprostenol : a single-dose compounding formulation for ovulation induction in beef cows

Abstract

While GnRH induces the preovulatory LH surge, PGF2α triggers luteolysis and uterine contraction. Therefore, Lecirelin-Cloprostenol combination given at the end of the TAI protocol may improve fertility in cows. Eight studies evaluated a novel Lecirelin-Cloprostenol (GPG) fixed-dose combination for ovulation and fertility in Nelore cattle subjected to timed artificial insemination (TAI) protocols. Initial experiments (Exp. 1, n = 28) showed GPG and GnRH induced earlier ovulation than PGF. In Exp. 2 (n = 25) and Exp. 4 (n = 17), the GPG protocol reduced the dispersion of ovulation timing compared to GnRH alone (Bartlett's test, P < 0.05). In Exp. 3, the GPG group had lower intrafollicular estradiol (P = 0.04) and higher PTGS2 gene expression (P = 0.05) compared to the GnRH group. Fertility outcomes varied: GPG tended (P = 0.1) to increase pregnancy per artificial insemination (P/AI) in postpartum cows (Exp. 5, n = 326) and improved ovulation rates when estradiol cypionate (EC) was used (Exp. 6, n = 17). While a large field study (Exp. 7, n = 948) showed no overall P/AI difference when the GPG treatment was given following estradiol cypionate. Finally, GPG and GnRH had similar P/AI (P = 0.3) in non-estrus cows (Exp. 8, n = 1692) compared to GnRH. In conclusion, GPG upregulated PTGS2 expression and decreased intrafollicular E2 concentrations in the ovulatory follicle relative to GnRH, providing a mechanistic basis for the improved ovulatory synchrony observed in GPG-treated cows. While the GPG formulation consistently reduced the dispersion of ovulation timing across experiments, effects on P/AI were marginal in the present study.