Reproductive performance of Zebu cattle in Mexico: 1. Sexual behavior and seasonal influence on estrous cyclicity

Abstract

Clinical observations were carried out on 32 and 38 nonpregnant Zebu females during the rainy and the dry season, respectively. Of the animals studied, 18 from the rainy season group and 13 from the dry season group failed to show estrus. The length of proestrus, estrus, and the ostrous cycle as well as ovulation time were determined only in 14 cyclic animals during the rainy season and in 25 cyclic animals during the dry season. Observations were made continuously (24 hours/day) during the 71 recorded estrous periods. Sexual behavior was recorded during proestrus and estrus. Proestrus was shorter in the dry period than in the rainy period (7.4 ± 8.7 hours vs 19.0 ± 17.5 hours; P<0.05). The duration of estrus was 10.3 ± 4.5 hours. In 60% of the cases, estrus started during the day, the frequency being higher during the dry than the rainy season (71% vs 40%; P<0.05). The estrous cycle was longer in the rainy period than in the dry period (21.5 ± 2.0 days vs 19.9 ± 1.4 days; P<0.05). Ovulation occurred 25.4 ± 5.9 hours after the onset of estrus. The length of estrus and ovulation time were positively correlated (r=0.64; P<0.05). Every day from Day 16 of the cycle until the following estrus, the external genital organs of the cows were checked and photographed, while the internal genital organs were palpated per rectum palpation. The sum of the estimates of the signs showed a daily increase when estrus approached and remained high during the day of estrus and the day of ovulation. The duration of estrus averaged 12.4 hours when the temperature was below 27°C and 9.3 hours when it was above 27°C (P<0.05).