Influence of suckling and side of corpus luteum or pregnancy on folliculogenesis in postpartum cows.

Abstract

This study was designed to evaluate follicular development of 30 postpartum beef cows: 15 were suckled, and calves were removed from the other 15 within 24 h after birth. Ovaries were removed on Day 5 postpartum and a total of 246 follicles greater than or equal to 3 mm in diameter was obtained. Estrogen was extracted from follicular fluid and quantitated by radioimmunoassay. Atresia for each follicle was assessed by 1) follicular estrogen concentrations, and 2) evaluating mitotic and pyknotic nuclei in granulosa cells. The average weight of the ovaries and corpus lutea (CLs) did not differ between cow treatments or between locations relative to the right or left ovary. Suckled cows had smaller and fewer follicles and follicular estrogen concentrations were lower compared with follicles from nonsuckled cows. The ovary with the CL which was ipsilateral to the uterine horn of the recent pregnancy (CL ovary) compared with the ovary without the CL (non-CL ovary) had smaller follicles and lower estrogen concentrations. Only 18% of the follicles on the CL ovary compared to 48% of the follicles on the non-CL ovary were classified as healthy. The interaction of suckling and the presence of the CL significantly depressed follicular development. Follicles on the non-CL ovary from nonsuckled cows had the greatest estrogen content and percent of healthy follicles. Suckling significantly decreased follicular estrogen concentrations and the percent of healthy follicles on the non-CL ovary, and estrogen concentrations and the percentage of healthy follicles were lowest on the CL ovary from suckled cows.