Luiz Francisco Machado Pfeifer, Cintia Batista Hurtado, Vanessa Lemos de Souza, Ingrid Pedraça Barbosa, Samira Alves de Souza Silva, Lígia Margareth Cantarelli Pegoraro, Renata Reis da Silva, Fabiane Pereira de Moraes, Natalia Avila de Castro, André Cascalho Andrade, Monique Tomazele Rovani, Bernardo Garziera Gasperin
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.