Maternal age influences the number of primordial follicles in the ovaries of yearling Angus heifers

Authors: TENLEY, SARAH - University Of Nebraska; SPURI GOMES, RENATA - University Of Nebraska; ROSASCO, SHELBY - New Mexico State University; NORTHROP, EMMALEE - South Dakota State University; RICH, JERICA - South Dakota State University; McNeel, Anthony; SUMMERS, ADAM - New Mexico State University; Miles, Jeremy; Chase, Chadwick - Chad; Lents, Clay; PERRY, GEORGE - South Dakota State University; WOOD, JENNIFER - University Of Nebraska; CUPP, ANDREA - University Of Nebraska; Cushman, Robert - Bob

Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2018
Publication Date: 1/20/2019
Citation: Tenley, S.C., Spuri Gomes, R., Rosasco, S.L., Northrop, E.J., Rich, J.J., McNeel, A.K., Summers, A.F., Miles, J.R., Chase, Jr., C.C., Lents, C.A., Perry, G.A., Wood, J.R., Cupp, A.S., Cushman, R.A. 2019. Maternal age influences the number of primordial follicles in the ovaries of yearling Angus heifers. Animal Reproduction Science. 200:105-112. https://doi.org/10.1016/j.anireprosci.2018.12.004.
DOI: https://doi.org/10.1016/j.anireprosci.2018.12.004

Interpretive Summary: Several studies have reported that age of dam influences the number of antral follicles detectable by ultrasonography in daughters at a year of age, because heifers born to mature cows have more follicles than heifers born to heifers. Antral follicle count is a diagnostic marker of the number of primordial follicles in the ovaries of heifers. Therefore, we hypothesized that heifers born to mature cows would have more primordial follicles in their ovaries at a year of age than heifers born to heifers. Ovaries were collected at slaughter and histological analysis was performed. Heifers born to mature cows had more primordial follicles than heifers born to heifers. These results confirm that the differences identified by ultrasonography are real and suggest that producers may wish to select replacement heifers that are born to mature cows, because previous studies have shown that heifers with greater numbers of follicles are more fertile.

Technical Abstract: The number of antral follicles detectable by ultrasonography in heifers is influenced by age of the dam, because daughters of primiparous cows have fewer antral follicles than daughters of mature cows. We, therefore, hypothesized that heifers with primiparous dams would have fewer primordial follicles in their ovaries than heifers born to mature (4+ y) cows. Angus heifers (n=464) were submitted for ultrasonographic evaluation of antral follicle number at 325, 355, and 385 d of age. Ovaries were collected from a random subset of heifers (n=79) and processed for histological evaluation to determine number of primordial follicles. A greater percentage of heifers with primiparous dams had a corpus luteum at first ultrasonographic examination; however, a greater percentage of heifers with multiparous dams had ovulated by the start of breeding (P < 0.01). Heifers with primiparous dams had fewer antral follicles detectable by ultrasonography (P < 0.01). Heifers with primparous dams had fewer surface antral follicles on their ovaries (P < 0.01), and the number of primordial follicles per histological section was less for heifers with primiparous dams (P= 0.02). These data indicate that the lesser number of antral follicles detectable by ultrasonography in heifers with primparous dams is due to less ovarian follicle reserves. Selecting replacement heifers from mature dams may result in daughters with greater fertility and reproductive longevity; however, further research is necessary to determine if interactions between size of the ovarian follicle reserve and age at puberty influence fertility and reproductive longevity in replacement heifers.