EFECTO DEL DESARROLLO DEL TRACTO REPRODUCTIVO Y TRATAMIENTO HORMONAL SOBRE LA ACTIVIDAD OVÁRICA DE NOVILLAS BOS INDICUS

Abstract

<p>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 <em>Bos indicus</em> heifers under humid tropical conditions. Twenty-four <em>Bos indicus</em> 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 (P<sub>4</sub>) 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 P<sub>4</sub> concentration were similar for both study group. In conclusion, RTD had effect on estrous behavior, however, ovulation, diameter of dominant follicle and plasma P<sub>4</sub> concentration of both groups (RTD and HT) were similar on estrous synchronization, in <em>Bos indicus</em> heifers under humid tropical conditions.</p>