Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: November 11, 2003
Publication Date: August 1, 2004
Citation: Cushman, R.A., Allan, M.F., Echternkamp, S.E. 2004. Factors affecting the development of preantral follicles in cattle [abstract]. Journal of Animal Science. 82 (Supplement 2):85. (Abstract #230) Technical Abstract: Preantral follicles comprise the largest portion of the follicles in the mammalian ovary, but the factors controlling activation of primordial follicles into the growing pool and growth of preantral follicles are poorly understood. Studies using transgenic mice and cultures of whole rodent ovaries provide most available data; however, information is beginning to accumulate for domestic ruminants. A number of model systems have demonstrated that, while beneficial, the gonadotropins, FSH and LH, are probably not required for early folliculogenesis. However, several members of the transforming growth factor-beta super family, including growth differentiation factor-9 (GDF-9), bone morphogenic protein-15 (BMP-15), and anti-Mullerian hormone (AMH), have demonstrated roles in activation and/or growth of preantral follicles in both rodent and ruminant models. MARC cattle selected for multiple ovulations have greater numbers of preantral and antral follicles, and provide a unique polygenic model for examining factors controlling preantral follicle development. It is unclear whether the increased ovulation rate in these cattle is due to increased numbers of primordial follicles or whether there are physiological mechanisms involved in enhanced follicular development beyond the primordial stage. Evidence from sheep indicates mechanisms that enhance follicular development. Booroola sheep have a mutation in the bone morphogenic protein receptor-1B (BMPR-IB) which results in an increased number of ovulations, and an inactivating mutation in the BMP-15 gene in Inverdale sheep blocks folliculogenesis at the primary stage, similar to GDF-9 deficient mice. No genes with a major effect on ovulation rate have been identified in the MARC Twinner cattle, but there is a QTL on chromosome 7, which maps closely to the GDF-9 and AMH genes. Treatment of ovarian cortical cultures with AMH decreased the diameter of primary follicles after 10 days, implicating AMH as an inhibitor of preantral follicle growth in cattle. Future studies will examine Twinner ovary function in culture.