Brangus cows have ovarian reserve parameters more like Brahman than Angus cows

Authors: Cushman, Robert - Bob; SOARES, EMERSON - Universidade Federal De Santa Maria; YAKE, HANNAH - University Of Tennessee; Patterson, Allyson; ROSASCO, SHELBY - New Mexico State University; BEARD, JOSLYN - New Mexico State University; NORTHROP, EMMALEE - South Dakota State University; RICH, JERICA - South Dakota State University; Miles, Jeremy; Chase, Chadwick - Chad; GONDA, MICHAEL - South Dakota State University; PERRY, GEORGE - South Dakota State University; McNeel, Anthony; SUMMERS, ADAM - New Mexico State University

Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2019
Publication Date: 8/20/2019
Citation: Cushman, R.A., Soares, E.M., Yake, H.K., Patterson, A.L., Rosasco, S.L., Beard, J.K., Northrop, E.J., Rich, J.J., Miles, J.R., Chase, C.C., Gonda, M.G., Perry, G.A., McNeel, A.K., Summers, A.F. 2019. Brangus cows have ovarian reserve parameters more like Brahman than Angus cows. Animal Reproduction Science. 209:106170. https://doi.org/10.1016/j.anireprosci.2019.106170.
DOI: https://doi.org/10.1016/j.anireprosci.2019.106170

Interpretive Summary: Female cattle of Bos indicus origin have naturally increased numbers of antral follicles compared to female cattle of Bos taurus origin; however, this does not result in increased fertility. Histological studies have reported no difference in total microscopic follicle numbers between the ovaries of Bos indicus females and Bos taurus females, but Bos indicus ovaries are larger than Bos taurus ovaries. This would imply that the follicle density within Bos indicus ovaries is diminished compared to Bos taurus ovaries. A collaborative effort with researchers at New Mexico State University and South Dakota State University demonstrated this to be true. These results indicate that when using ultrasonography to predict numbers of follicles in Bos indicus ovaries and associate this with fertility, a greater antral follicle count will be necessary to predict fertility traits associated with the number of follicles in the ovaries. Furthermore, these data suggest that Bos indicus ovaries may be less supportive of microscopic follicle growth and development.

Technical Abstract: Bos indicus females have more surface antral follicles than Bos Taurus females; however, histological studies demonstrated no difference in total number of primordial follicles between these two biological types of cattle. Primordial follicle density in the ovary was less in Nelore ovaries compared to Angus ovaries, but no studies have examined the primordial follicle density in Bos indicus cross-bred females. It, therefore, was hypothesized that primordial follicle density in the ovary would decrease as percentage Bos indicus increased. Ovaries were collected from cross-bred Angus (n = 32, no Bos indicus influence), Brangus (n = 15), or Brahman (n = 9) cows and pre-pared for histological evaluation. There was no difference in total number of primordial follicles per ovary between breeds (P > 0.10). When numbers of primordial follicles were expressed on a per gram of ovarian tissue basis, there were fewer primordial follicles per gram of ovarian tissue in Brangus and Brahman cows than in Angus cows (P < 0.05). Brangus cows did not differ from Brahman cows in primordial follicle density (P > 0.10). Differences in primordial follicle density could indicate differences in capacity of ovarian stroma to produce factors necessary for oogonial proliferation and primordial follicle formation among breeds. Identifying these factors could improve the approach for culturing pre-antral follicles of cattle. Furthermore, these results explain why ultrasonographic antral follicle counts may need to be adjusted to a greater threshold to predict size of ovarian reserve and determine ovarian reserve related reproductive traits in Bos indicus females.