Influence of plasma estradiol 17-β and progesterone levels on estrous behaviour in mithun ( Bos frontalis)

Abstract

The study was conducted on 10-adult mithun ( Bos frontalis) cows during the third or fourth postpartum estrous cycle to investigate the influence of plasma estradiol 17-β (E2) and progesterone (P4) levels on the expression of behavioural estrus. The estrus was detected in the mithun cows by bull parading and the patterns of behavioural estrus were recorded. The estrous intensity score (EIS) was assigned according to the visible signs in cows and bull activities. The daily blood samples throughout the estrous cycle were collected by jugular venipuncture and were analysed for E2 and P4 through ELISA. The variations in E2 and P4 concentrations were analysed by repeated measurement ANOVA. The model included the day of estrous cycle and EIS as source of variation. The association of EIS with E2 and P4 was established by the partial correlation analysis. The average estrous cycle length was found 21.3 ± 0.4 days. The average duration ( h) of estrus and standing heat were recorded 67.2 ± 7.2 and 10.5 ± 2.7, respectively. The expression of behavioural estrus was found silent. In the entire estrous cycle, two prominent E2 peaks were observed approximately on day 1 and 17. The peak E2 concentration on day 17 was found significantly ( p < 0.01) higher than the peak E2 concentration on day 1. The P4 concentration was found to be lowest ( p < 0.01) on the day of estrus. The P4 concentration was increased gradually from day 1 to 6 of the cycle. The P4 concentration was increased sharply and from day 7, attained peak concentration on day 11 and decreased thereafter. The EIS was found to be associated more closely with the basal concentrations of E2 and P4, and with the E2:P4 ratio of the cycle. The study revealed that the P4 concentration was instrumental in relation to the E2 concentration for the behavioural expression of estrus in this species. The low expression of behavioural estrus was probably due to the overall low P4 concentration during the entire estrous cycle.