GnRH analogs induce a LH peak and increase pregnancy per timed-AI in ewes

To date, there have been no studies testing the capacity of GnRH analogs and respective doses to induce a LH peak in sheep. In this sense, the present study aimed to evaluate the capacity of different synthetic forms and doses of GnRH in inducing LH release in sheep, and the effect of GnRH administration at timed artificial insemination (TAI) on pregnancy per timed-AI. In experiment 1, ewes (n = 40) received an intravaginal device (IVD) of medroxyprogesterone acetate (MPA; 60 mg) for 7 d and prostaglandin F2α analog on Day 5. On Day 7, the ewes were allocated randomly into one of eight groups (n = 5/group), which received a GnRH analog at a specific dose, as follows: lecirelin (12.5 or 25 μg), gonadorelin (50 or 100 μg), buserelin acetate (4.2 or 8.4 μg), or deslorelin (375 or 750 μg). Blood samples for LH determination were obtained at 0, 2, 4, and 6 h after GnRH and the IVDs were removed after the last blood collection. The maximal LH concentration induced by gonadorelin at doses of 50 μg and 100 μg (12.0 ± 2.4 ng/mL and 28.6 ± 7.1 ng/mL, respectively) was lower (P 0.05) to the 100 μg of gonadorelin. The total release of LH (area under the curve – AUC) after treatment with 50 μg of gonadorelin (31.7 ± 5.9 ng h/mL) was lower (P