Location: Livestock Bio-Systems
2020 Annual Report
Objectives
Objective 1: Apply developmental programming to improve production efficiency of beef cattle.
Sub-objective 1.A: Apply fetal programming to improve progeny performance.
Sub-objective 1.B: Apply nutritional programming in the peri-pubertal period to improving performance.
Objective 2: Identify genetic and epigenetic mechanisms that contribute to early embryonic development.
Sub-objective 2.A: Determine the influence of resveratrol on early embryonic development.
Sub-objective 2.B: Determine the influence of non-esterified fatty acids on early embryonic development in cows differing in antral follicle number.
Sub-objective 2.C: Determine the influence of a loss of function polymorphism in the follicle stimulating hormone receptor gene on cumulus cell function and early embryonic development.
Objective 3: Identify maternal contributions to progeny performance.
Sub-objective 3.A: Identify contributions of uterine proteins to conceptus development in beef heifers differing in antral follicle number.
Sub-objective 3.B: Determine the influence of age of dam on progeny performance.
Approach
Beef heifers that conceive early in their first breeding season have greater reproductive longevity and enhanced lifetime productivity. We reported that this is due, in part, to an increase in the number of antral follicles in their ovaries without any difference in Reproductive Tract Score or age at puberty. In the previous project period, we applied developmental programming (i.e., nutritional modifications at key stages of development) to heifers to increase the percentage that conceived early in their first breeding season and to increase the numbers of primordial follicles in their ovaries. The current project plan will determine if this resulted in increased reproductive longevity for these heifers and validate models that report the use of developmental programming to improve carcass characteristics in steer progeny (Objective 1). In Objective 2, we will investigate how nutrition and hormonal environment can impact the function of the genome during early embryonic development to better understand the factors contributing to fetal programming. In Objective 3, we will examine the maternal contributions to developmental programming by examining the influence of uterine function on conceptus development and the age of the dam on progeny performance. This research is critical to understand how early life events can impact adult traits and how we can harness developmental programming to improve the efficiency of beef production.
Progress Report
Calf performance measurements were collected for experiments in Objectives 1 and 3. The third year of data collection was completed to examine the influence of a polymorphism in the follicle stimulating hormone (FSH) receptor on early embryonic development in vitro (Objective 2C). The second year of data were collected for Objective 3A, examining conceptus development in heifers that differ in antral follicle number. Preliminary data indicate that conceptuses are shorter and conception rates are decreased in heifers with diminished numbers of follicles. Uterine function during the window of recognition of pregnancy may be enhanced in heifers with increased numbers of follicles compared to heifers with diminished numbers of follicles. This would provide a physiological mechanism that would lend credence to the increased frequency of pregnancy observed in heifers with increased numbers of follicles in the production setting.
Accomplishments
1. Developmental programming of the ovary in replacement beef heifers. Over-feeding replacement heifers during the development phase can be detrimental to their reproductive longevity. Past research from our laboratory demonstrated that placing heifers on a stair-step diet between weaning and breeding decreased development costs, adapted the heifers to reduced caloric environments they can encounter as cows on grass, and increased the number of eggs in their ovaries entering the first breeding season. One mechanism by which this increase in eggs in the ovaries might happen is a slowing of the entry of eggs into the growing pool. A study was performed by an ARS researcher at Clay Center, Nebraska, in collaboration with the University of Nebraska-Lincoln, to examine the rate of growth of eggs in cultured ovarian pieces from heifers that were developed on a stair-step diet compared to cultured ovarian pieces from heifers that were developed at a constant rate of gain. There was no difference in the rate of eggs entering the growing pool between development diets, suggesting that new egg formation is occurring to increase the numbers in stair-step heifers. Cow-calf producers can improve fertility and reproductive longevity in replacement females by developing them on a stair-step protocol.
2. Disruption of the biological clock alters estrous cycle and fertility parameters in beef heifers. Estradiol from the ovary plays a critical role in uterine function and recognition of pregnancy. In this study, ARS researchers at Clay Center, Nebraska, in collaboration with South Dakota State University, investigated how estradiol influences timing of conception and recognition of pregnancy in beef cows. Cows that did not respond properly to a hormonal synchronization protocol and had low circulating concentrations of estradiol were less likely to have a normal estrous cycle and conceived very late in the breeding season or were not pregnant. Biochemical analysis of uterine tissues demonstrated that the biological clock was disrupted in the uterus of heifers that had low circulating concentrations of estradiol. To improve fertility in beef cows, cow-calf producers should apply management strategies that maximize estradiol production by the ovary at the start of the breeding season.
3. Antral follicle count is beneficially associated with calving day in replacement beef heifers in Uruguay. Beef heifers that give birth early in their first calving season have greater lifetime productivity. A collaborative study was performed by ARS researchers at Clay Center, Nebraska, and the University of Uruguay to examine the relationship between age at puberty and antral follicle count in beef heifers in Uruguay. Heifers that attained puberty earlier conceived earlier but were larger and had greater fat deposition than heifers that attained puberty later in the breeding season. Heifers with increased numbers of antral follicles conceived earlier but did not differ from heifers with diminished numbers of follicles in body size or fat deposition. There was no interaction between age at puberty and antral follicle count for any of the parameters examined. Selecting replacement heifers based on antral follicle counts will allow cow-calf producers to increase fertility and reproductive longevity without increasing cow size.
Review Publications
Abedal-Majed, M.A., Kurz, S.G., Springman, S.A., McNeel, A.K., Freetly, H.C., Largen, V., Magamage, M., Sargent, K.M., Wood, J.R., Cushman, R.A., Cupp, A.S. 2020. Vascular endothelial growth factor A isoforms modulate follicle development in peripubertal heifers independent of diet through diverse signal transduction pathways. Biology of Reproduction. 102(3):680-692. https://doi.org/10.1093/biolre/ioz211.
Cushman, R.A. 2019. Changing views on the role of the uterus in post-partum reproductive function in beef cows. Journal of Animal Science. 97(10):4021-4022. https://doi.org/10.1093/jas/skz287.
Perry, G.A., Cushman, R.A., Perry, B.L., Schiefelbein, A.K., Northrop, E.J., Rich, J.J., Perkins, S.D. 2019. Role of preovulatory concentrations of estradiol on timing of conception and regulation of the uterine environment in beef cattle. Systems Biology in Reproductive Medicine. 66(1):12-25. https://doi.org/10.1080/19396368.2019.1695979.
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.
