Blood were collected daily from 16 Nelore heifers confined, for radioimmunoassay (RIA).analyses of progesterone The plasma progesterone assay were at day zero (estrus) and at each three days until the -1 and the day zero.again The animals were divided in two groups: 1) with regular estrous cycle of 21 days (heifers with two and three follicular growth waves) and 2) with prolonged estrous cycle, greater than 25 days (heifers with four follicular growth waves). The mean plasma progesterone level from the animals during the estrous cycle differed between the two groups, being greater (4,27 ng/mL) for the extended cycles.(above 25 days; 4,27 ng/mL) than for the regular estrous cycle (21 days; 2,54 ng/mL). Results suggest that those heifers which showed an extended estrous cycles, needs an additional time for the follicles to each the pre-ovulatory stadium, resulting in prolonged and increased progesterone secretion.
follicular waves; heifer; Nellore; progesterone; radioimmunoassay
