EFFECT OF REPRODUCTIVE TRACT DEVELOPMENT AND HORMONAL TREATMENT ON OVARIAN ACTIVITY OF BOS INDICUS HEIFERS

Abstract

Evaluation of the reproductive tract development (RTD) is a criterion rarely used when heifers are included in estrous synchronization programs. The objective was to determine the effect of RTD and hormonal treatment (HT) on estrous and ovarian activity in Bos indicus heifers under humid tropical conditions. Twenty-four Bos indicus heifer were synchronized using a bovine intravaginal device (BID), divided according to RTD (immature or mature) and HT (estradiol cypionate or estradiol benzoate). Estrous was recorded from 24 to 60 h after BID removal. Follicular monitoring was evaluated by ultrasound every 12 h from BID removal until ovulation. Blood samples were taken on day 0, 3, 8 and 15 post BID removal to estimate progesterone (P4) concentration. Data were analyzed by analysis of variance and logistic regression procedures. There was no interaction between factors (P > 0.05). The highest percentage of estrous was found in heifers with mature RTD (91.7%, P < 0.05). The interval BID withdrawal to estrous (50.0±2.6 h), the proportion of heifers that ovulated (100%), the interval BID withdrawal-ovulation (75.0±2.1 h), and the time between onset of estrous and ovulation (24.5±2.2 h) were similar between immature and mature reproductive tracts and between HT. In addition, the growth of dominant follicles and P4 concentration were similar for both study group. In conclusion, RTD had effect on estrous behavior, however, ovulation, diameter of dominant follicle and plasma P4 concentration of both groups (RTD and HT) were similar on estrous synchronization, in Bos indicus heifers under humid tropical conditions.