Ultrasonographic evaluation of the follicular dynamics in crossbred dairy cows and heifer

An ultrasonographic study was performed to evaluate, three time per week, the follicular development, levels of progesterone (P4), characteristics of the corpus luteum (CL) and pattern of follicular growth during the first estrous cycle in 6 postpartum cows and during a given estrous cycle in 9 heifers. The study was undertaken at the farm "La Esperanza" of the Zulia University, located in a dry tropical forest area, characterized by a mean temperature of 28 degrees C and annual rainfall of 996 mm. A mean of 2.83 follicular waves were observed during the postpartum period; the first dominant follicle (DF) and the ovulatory follicle (OF) were observed at 18.1 and 30.5 days, respectively. The OF reach a mean greater diameter of 12.7 mm, 35 days postpartum. During the estrous cycle, a two-wave follicular development pattern was detected in 67% and 78% of the cows and heifers, respectively. The DF reach a mean greater diameter of 11.9 mm on day 8.5 in cows, and 9.8 mm on day 12.3 in heifers. The OF reach a mean greater diameter of 12.1 mm on day 21.3 vs 11.8 on day 20.7 of the cycle in cows and heifers, respectively. An mean maximum CL diameter of 1.8 and 1.9 cm was observed in cows and heifers, respectively. The mean P4 level during the diestrus was 0.89 ng/ml in cows and 2.7 ng/ml in heifers. Correlation values of 0.48 (P < .07) and 0.28 (P < .04) between the size of the CL and P4 levels were obtained during the estrous cycle in cows and heifers, respectively.