Induction of ovulation and estrus in the postpartum cow by using progesterone : determination of progesterone in peripheral blood

Abstract

A trial was performed attempting to shorten the postpartum interval of nursing cows by administration of exogenous progesterone (P) (4-pregnene-3, 20-dione) alone or combined with estradiol valerate (1,3,5, [10]-estratriene-3, 17β-diol-17 - valerate). Thirty cows of Angus and Hereford origin were randomized in a 2 x 3 factorial experiment with two times of postpartum treatment initiation (days 10 and 15) and three treatments, as follows: a vaginal pessary containing 3 g progesterone and maintained in place for nine days, the progesterone pessary plus 10 mg estradiol valerate 24 hours after the pessary withdrawal, and control cows. The pessary retention was 100 percent for the nine days of implant and the release of progesterone from the same was satisfactory. The average levels of P in peripheral blood reached a maximum of 3.6 ng/ml serum at day 1 after implant insertion and the minimum average was 2.2 ng/ml serum at day 9. Time of implant differences were nonsignificant but differences due to cows within treatment were significant. The results for postpartum return to estrus and endogenous progesterone surge indicated that there were nonsignificant differences due to time of start of the treatment or treatment itself. The breed differences were significant for percent of cows coining in estrus before 100 days postpartum (67% Angus vs 25% Hereford), and these differences were significant for progesterone surge when six young cows were eliminated from the analysis (79% Angus vs 29% Hereford). Even though treatments were nonsignificantly different, the observation of the ovarian activity and progesterone surge postpartum indicated that some success was obtained with the progesterone + estradiol valerate combination initiated at day 10. Since none of the treatments was highly effective in starting ovarian activity, it might be concluded that other endocrine factors not considered in this experiment are playing an important role in the postpartum return to estrus and ovulation.