Effect of gonadorelin, lecirelin, and buserelin on LH surge, ovulation, and progesterone in cattle.

ABSTRACT

Analogs of gonadoliberin (GnRH) are widely used in cattle to synchronize estrus and to induce ovulation, as well as for the treatment of ovarian cysts. The aim of this study was to compare the plasma profiles of LH and progesterone and the follicular dynamics in response to the administration of gonadorelin, lecirelin, or buserelin at the dose recommended to induce ovulation. In addition, the biological response to a half dose of lecirelin was assessed. Twelve healthy Holstein female cows were divided into four sequence groups, according to a Latin square design and received the four treatments during the four periods of the study. Before each period, the estrous cycle was synchronized, and on Day 6 or 7 of the ensuing cycle, the time at which it was most likely to have a dominant follicle, 100 µg of gonadorelin, 25 µg of lecirelin, 50 µg of lecirelin, or 10 µg of buserelin was administered to the cows. Blood samples were regularly collected for up to 4 days after the GnRH administrations. The plasma LH response was evaluated for up to 6 hours after administration, and the plasma progesterone response and ovarian follicular dynamics were evaluated for up to 4 days. There was a significantly lower LH release after gonadorelin treatment compared to lecirelin at the doses of 25 or 50 µg and the buserelin treatment. The mean maximal LH concentration after gonadorelin treatment was 2.5 lower than after lecirelin or buserelin treatment and was reached 1 hour earlier. Four days after the GnRH administration (i.e., at Days 10-11 of the estrous cycle), the overall mean increase in plasma progesterone concentration was 70% and did not differ between the treatment groups. The percentage of disappearance of the dominant follicle (84.8% of ovulation and 4.3% of luteinization) after GnRH treatment was high (73%, 82%, 100%, and 100%, for gonadorelin, lecirelin at the doses of 25 and 50 µg, and buserelin, respectively) and did not differ between the GnRH treatments. The follicle disappearance was followed by the emergence of a synchronous follicle wave within 2 days in almost all the heifers. Altogether, our data show that the three GnRH analogs, at the doses indicated for the induction of ovulation or at a half dose for lecirelin, are almost equally effective to induce the disappearance of the dominant follicle at Day 6 to 7 of the estrous cycle.