Follicular development and LH peak on Nellore (Bos taurus indicus) females with synchronized ovulation

Abstract

The objective with this work was to monitor ovarian activity and the moment of LH pre-ovulatory peak in Nellore heifers and cows submitted to a hormonal protocol for ovulation synchronization with norgestomet (NOR), estradiol benzoate (EB) and cloprostenol. In experiment 1, five cows and five heifers received application of 2.0 mg of EB and implant of NOR on day zero (D0), with removal on D8 following application of 0.5 mg of cloprostenol. On D9 1.0 mg of EB was applied, performing ultrasound monitoring of ovarian activity since the beginning of the protocol until ovulation. In experiment 2, six females in each category were submitted to the same treatment. Twenty seven hours after BE blood was collected every 15 minutes, over a six hours period, for determination of LH serum levels. The mean diameter of the ovulatory follicle was 8.02±0.39 mm in heifers and 9.10±0.24 mm in cows (P<0.05). The LH pre-ovulatory peak occurred, on average, 28.20±0.55 hours after the application of EB in cows. We can conclude that follicular development in Nellore heifers and cows submitted to ovulation synchronization occurs in a similar way, being the largest ovulatory follicle in cows. It’s suggested that in heifers LH peak probably occurs earlier than in cows.