Serum LH peak and ovulation following synchronized estrus in goats

Abstract

This study was aimed at comparing the temporal relationship between estrus, the LH peak and ovulation following estrous synchronization in goats using medroxiprogesterone acetate (MGA) or fluorogestone acetate (FGA). Twenty-four cyclic goats were randomly assigned to two treatments: MGA group ( n = 12) that individually received a daily oral dose of 0.22 mg MGA for 12 days, and a FGA group ( n = 12) treated for 12 days with intravaginal sponges containing 45 mg FGA. The goats from both groups were treated with a prostaglandin analogue (75 μg Cloprostenol i.m.) during the last day of their progesterone treatment. Estrous detection was carried out every 4 h after the end of the treatment, and blood samples for the determination of the serum LH concentrations collected at 2 h intervals for 24 h from the onset of estrus. Ovulation was detected with the aid of transrectal ultrasonography, performed every 4 h starting 15 h after the onset of estrus. All goats showed estrus. In the MGA group the onset of estrus occurred later and was more variable in relation to the end of treatment (86.7 ± 3.9 h), compared to the FGA group (44.4 ± 1.5 h; P < 0.01). The interval between the LH peak and ovulation was significantly ( P < 0.05) longer in the MGA group (26.2 ± 1.1 h) than the FGA group (22.4 ± 0.8 h). There were no differences regarding the intervals from the onset of estrus to the LH peak (14.9 ± 1.8 and 15.3 ± 0.9 h) and to ovulation (40.1 ± 2.3 and 37.6 ± 0.5 h) for the MGA and FGA groups, respectively. The amplitude of the LH peak was not different between groups. It could be concluded that the timing of the LH peak and ovulation is not related to the end of treatment, but with the time of onset of estrus. The longer and more variable interval for estrous demonstration following MGA treatment, represents a serious limitation for its use in synchronization programs in goats, where mating is to be performed on a fixed-time basis.