|Cushman, Robert - Bob|
Submitted to: Biology of Reproduction
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/4/2001
Publication Date: 8/20/2001
Citation: Cushman, R.A., Desouza, J.C., Hedgpeth, V.S., Britt, J.H. 2001. Alteration of activation, growth, and atresia of bovine preantral follicles by long-term treatment of cows with estradiol and recombinant bovine somatotropin. Biology of Reproduction. 65(2):581-586. Interpretive Summary: Because we have demonstrated a positive relationship between microscopic populations of follicles in the ovary and ovulatory response in cattle, we assessed the effects of long-term treatment with estradiol and growth hormone on microscopic follicle numbers in the bovine ovary. Ovaries were collected from cows treated for 75 days with estradiol and growth hormone. This treatment has been previously demonstrated to enhance superovulatory response to gonadotropins in cattle. Microscopic analysis revealed that treatment with estradiol stimulated follicles to enter the growing pool follicles. After follicles had entered the growing pool, growth hormone enhanced survival of the growing follicles. Therefore, long-term treatment with estradiol and growth hormone increase microscopic follicle growth and survival and results in increased responsiveness to gonadotropins at the time of superovulation.
Technical Abstract: The hypothesis was that long-term treatment of cattle with estradiol (E2) and bovine somatotropin (bST) would alter the earliest stages of folliculogenesis. Nonlactating Holstein cows (n = 26) were treated in a 2 x 2 arrangement with E2 (2 x 24 mg implants, 67.1 +/ 1.4 days) and bST (Posilac, 63.6 +/ 1.5 days). At Day 67 +/ 1.3, one ovary was removed for morphometric and immunohistochemical analysis. For each ovary, 388 +/ 38 microscopic fields (2 x 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 = 100 per ovary) were further classified as containing no evidence of follicles or containing atretic remnants of follicles. Approximately 30 4-um sections per ovary were stained for proliferating cell nuclear antigen (PCNA), and 150 fields per ovary were evaluated. Additional sections (n = 10 per ovary) were assessed immunohistochemically for apoptosis, and fluorescence intensity was determined for each follicle. Treatment with bST significantly decreased percentage of empty fields containing 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 + E2 decreased apoptosis as shown by decreased fluorescence intensity. Thus, E2 induced activation of follicles, bST enhanced survival, and the combination lowered atresia.