Ovarian follicular development in cows, sows and ewes in different stages of pregnancy as affected by number of corpora lutea in the same ovary.

The distribution of arbitrarily-classed large (~>4 mm dia.) and small (<4 mm dia.) follicles between the ovary with the lesser number of corpora lutea and the ovary with the greater number of corpora lutea was studied in pregnant cows, sows and ewes. At mid-pregnancy in the cow, numbers of large follicles reached a low level and remained at that level to the end of pregnancy on the ovary that contained a corpus luteum; the number of large follicles did not decrease until late pregnancy on the ovary without a corpus leuteum. In the pregnant ewe, large follicles were present only at days 7 and 3 5, at which times they were present in greater numbers on the ovary containing a corpus luteum. At days 75 and 120 of gestation in ewes, the volume of small follicles was less for the ovary contffining a corpus luteum. In the sow, the ovary with the greater" number of corpora lutea also possessed the greater number of small and total follicles throughout pregnancy. Differences associated with stage of gestation in all three species were characterized by changes in the distribution of follicles between large and small sizes and not in the total number of follicles. Large follicles were least evident in late pregnancy in all ~hree species, and were also present in low numbers early in gestation in the cow and sow. (