Characterization of the LH peak after short and long fixed-time artificial insemination protocols in sheep raised in the tropics

Abstract

The aim of this study was to evaluate the peak in luteinizing hormone (LH) and the pregnancy rate of sheep (Texel × Santa Inês) in the tropics using short- (6 days) and long-term (12 days) progesterone protocols followed by artificial insemination (AI) both in and out of the breeding season. Experiment 1 was conducted within (IN) the breeding season (autumn, n = 36), and experiment 2 was conducted outside (OUT) of the breeding season (spring, n = 43). In each experiment, the sheep were divided into two groups (6 or 12 days) according to the duration of treatment with a single-use progesterone release vaginal device (CIDR®, Pfizer, São Paulo, SP, Brazil), and blood samples were collected from 10 animals per group every 4 hr to measure the LH and progesterone concentrations. In the spring, the characteristics of the LH peak did not differ between groups; but in the autumn, there were differences between groups at the beginning (G-6 IN: 36.44 ± 5.46 hr; G-12 IN: 26.57 ± 4.99 hr) and end of the LH peak (G-6 IN: 46.22 ± 7.51 hr; G-12 IN: 34.86 ± 8.86 hr). The results showed alterations in the LH peak during the breeding season only in the sheep undergoing the short-term protocol.