Numbers of primordial and primary follicles (mean number per section ± SEM; n = 6 cultures, 2 from each of 3 fetuses) in ovarian cortical pieces cultured for 10 d in control medium (Con) or with the phytoestrogen genistein (Gen) or the environmental estrogens bisphenol A (BPA) or octylphenol (Oct-P), all at 0.1 μM. Ovarian pieces were isolated from ovaries of bovine fetuses at 100 to 120 d, a time when follicle formation is in progress. Means with no common letters (a,b,c) are different (P < 0.05).