Alteration of Activation, Growth, and Atresia of Bovine Preantral Follicles by Long- Term Treatment of Cows with Estradiol and Recombinant Bovine Somatotropin

The hypothesis was that long-term treatment of cattle with estradiol (E2) and bovine somatotropin (bST) would alter the ear-liest stages of folliculogenesis. Nonlactating Holstein cows (n 5 26) were treated in a 2 3 2 arrangement with E2 (2 3 24 mg implants, 67.1 6 1.4 days) and bST (Posilac, 63.6 6 1.5 days). At Day 67 6 1.3, one ovary was removed for morpho-metric and immunohistochemical analysis. For each ovary, 388 6 38 microscopic fields (2 3 2 mm) were examined and follicles within each field were classified by histological stage. Fields that contained no follicles were classified as empty. Empty fields (n 5 100 per ovary) were further classified as containing no evidence of follicles or containing atretic remnants of follicles. Approximately 30 4-mm sections per ovary were stained for pro-liferating cell nuclear antigen (PCNA), and 150 fields per ovary were evaluated. Additional sections (n 5 10 per ovary) were assessed immunohistochemically for apoptosis, and fluores-cence intensity was determined for each follicle. Treatment with bST significantly decreased percentage of empty fields contain-ing atretic remnants. Treatment with E2 induced activation of follicles as shown by a decrease in percentage of primordial follicles and an increase in percentage of primary follicles as determined by PCNA staining. At the primary follicle stage the combination of bST 1 E2 decreased apoptosis as shown by de-creased fluorescence intensity. Thus, E2 induced activation of follicles, bST enhanced survival, and the combination lowered atresia. apoptosis, estradiol, follicle, growth hormone, ovar