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Regular Article |
` Department of Anatomy, Physiological Sciences and Radiology, North Carolina State University, Raleigh, North Carolina 27606
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-µm 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.
First decision: 13 March 2001.
1 Correspondence: Jack Britt, University of Tennessee, Institute of Agriculture, P.O. Box 1071, Knoxville, TN 37901-1071; FAX: 865-974-8781; jack-britt{at}utk.edu
2 Current address: VRT6-0016B, Biomedical Sciences, Cornell University, Ithaca, NY 14853.
3 Current address: Departamento de Zootecnia, Universidade Federal de Lavras, C P 37, 37200-000 Lavras MG, Brazil.
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