- The current focus of our USDA-AFRI funded research is to investigate the impact of prenatal and early postnatal nutrition on neuroendocrine mechanisms that underlie the process of sexual maturation in heifers.
- To develop practical approaches for translating fundamental knowledge in neuroendocrinology/reproductive biology into managerial strategies to program the timing of puberty.
- Assess the interaction of pre- and postnatal nutrition on adult reproductive phenotype in beef females.
A secondary goal is to optimize strategies for synchronization of ovulation and fixed-time artificial insemination (FTAI) in Bos indicus-influenced beef females which predominate in the southern Gulf Coast regions of the US and throughout many parts of the world. This work has resulted in the development of two protocols, Bee Synch I and II, which have greatly enhanced the ability to achieve high FTAI pregnancy rates (>50%) in these types of cattle, with Bee Synch II now considered the preferred methodology in mature cows. Ongoing research is directed toward the optimized use of Bee Synch II in Bos indicus-influenced and purebred Bos indicus heifers.
Based on the hypothesis that the period between 4 and 7 mo of age is critical for nutritional programming of brain functions leading to early onset of puberty, we have examined the ability of a stair-step compensatory gain nutritional regimen to optimally program the timing of puberty at 11-12 mo of age in Bos indicus-influenced beef heifers. Heifers were fed ad libitum a high-concentrate diet or had restricted intake of a low-concentrate diet in alternate periods of 10 wk. We observed that the proportion of heifers pubertal by 12 mo of age was similar between heifers fed a high concentrate diet throughout the experimental period (High Control group) and those fed ad libitum a high concentrate diet from 4 to 6.5 mo of age, restricted markedly from 6.5 to 9 mo of age, and then fed ad libitum again from 9 to 11.5 mo of age. In contrast, the proportion of heifers pubertal by 12 mo of age in the reverse stair-step compensatory gain group (SSC-2) was lower than the control and SSC-1 groups, and not different than the Low Control (LC) group at 12 mo; however, by 14 mo of age approximately 90% of heifers in the SSC-2 group had also attained puberty compared to only 40% of the LC group. These results indicate that functional alterations occurring in the brain during the early juvenile period (between 4 and 7 mo of age in the heifer) can program the timing of puberty that occurs months later.
Our fundamental studies related to the programming of puberty in heifers have demonstrated that increased planes of nutrition during juvenile development lead to organizational and functional changes in hypothalamic (lower brain) pathways comprising specific signaling peptides: neuropeptide Y (NPY), proopiomelanocortin (POMC, the precursor of αMSH), and kisspeptin. Changes include alterations in the abundance of NPY, POMC, and mRNA for the kisspeptin gene, Kiss1, and in the plasticity of the neuronal projections to GnRH neurons. Results also show that epigenetic mechanisms, such as modifications in the DNA methylation pattern, are involved in this process. Recent experiments have also shown that maternal nutrition during gestation can induce morphological and functional changes in the hypothalamus of heifer offspring that are likely to persist long after birth. These organizational changes occurring during fetal development have the potential to not only impact puberty but also influence reproductive performance throughout adulthood. With respect to puberty, maternal undernutrition during mid- to late gestation in the beef cow may not impact age at puberty in offspring if postnatal nutrition is adequate to compensate. However, restricted postnatal nutrition from 4 to 8 months of age delays puberty at least 2 months, and a combination of pre- and postnatal restriction may delay puberty by at least 3 months. Importantly, this leads to functional alterations in brain circuitries that probably underlie lifelong perturbations in metabolic and reproductive efficiency. The costs to cattlemen of such commonly-occurring nutritional events are estimated to equal as much as 16% of total annual production expenses.
The 5-Day Bee Synch + CIDR (Bee Synch I) protocol and modified procedure (Bee Synch II) have revolutionized the ability of cattlemen to synchronize ovulation for fixed-time artificial insemination (FTAI) of Bos indicus-influenced beef cows in the US using commercially-available, FDA-approved products. Bos indicus-influenced beef cows comprise 30-40% of the U.S. beef herd and 60-70% globally. Bee Synch II reduces drug costs compared to Bee Synch I, consistently results in FTAI pregnancy rates of ≥ 50% in well-managed herds and increases the proportion of AI calves relative to conventional methods by up to 15%.
Gary L. Williams
- Carlos Serna
- Viviana Garza
- Dr. Rodolfo Cardoso
- Dr. Randy Stanko
- Williams, G.L. and R.L. Cardoso. Neuroendocrine control of estrus and ovulation. In Bovine Reproduction, Edited by Hopper R. 2020; Wiley-Blackwell, Hoboken, NJ USA. (2nd Edition; in press)
- Williams, G.L., B.R.C. Alves, R.C. Cardoso. Female Puberty: Nutrition and Endocrinology. In Encyclopedia of Reproduction, 2018; Elsevier, New York, NY USA. http://dx.doi.org/10.1016/B978-0-12-801238-3.64647-0. ISBN: 9780128118993
- Amstalden, M, G.L. Williams. Neuroendocrine control of estrus and ovulation. In Bovine Reproduction, Edited by Hopper R.; Wiley-Blackwell, Hoboken; 2015, NJ USA
- Cardoso, R.C., S.M. West, T.S. Maia, B.R.C. Alves, G.L. Williams. Nutritional control of puberty in the bovine female: prenatal and early postnatal regulation. Dom. Anim. Endo. 2020 https://doi.org/10.1016/j.domaniend.2020.106434
- Williams, G.L., R.L. Stanko. 2020. Pregnancy rates to fixed-time AI in Bos indicus influenced beef cows using PGF2α with (Bee Synch I) or without (Bee Synch II) GnRH at the onset of the 5-Day CO-Synch + CIDR protocol. Theriogenology 142:1-7. http://dx.doi: 10.1016/j.theriogenology.2019.09.047).
- Cardoso R.C., Alves B.R.C, Williams G.L. 2018. Neuroendocrine signaling pathways and the nutritional control of puberty in heifers. Reproduction in Domestic Ruminants IX: Proceedings of the 10th International Symposium on Ruminant Reproduction. Anim. Reprod. 15, (Suppl.1): 868-878. http://dx.doi.org/10.21451/1984-3143-AR2018-0013
- O’Neil, M.M., C. M. Korthanke, J. O. Scarpa, S. T. Jaques, T. H. Welsh, Jr., R. C. Cardoso, G. L. Williams. 2019. Differential regulation of gonadotropins in response to continuous infusion of native GnRH in the winter anovulatory mare and effects of exogenous treatment with estradiol-17β. J. Equine Vet. Sci. 75:93-103. doi: 0.1016/j.jevs.2019.01.013
- Scarpa, J.O., M.M. O’Neil, R.C. Cardoso, G.L. Williams. 2019. Use of prostaglandin F2α with or without GnRH at the onset of a 5-Day CIDR-based protocol for synchronization of ovulation in Bos indicus-influenced cows: Ovarian follicular and luteal dynamics. Anim. Reprod. Sci 204:1-9 doi: 10.1016/j.anireprosci.2019.02.013
- Bedenbaugh M.N., M. D’Oliveira, R.C. Cardoso, S.M. Hileman, G. L. Williams, M. Amstalden. 2018. Pubertal escape from estradiol negative feedback in ewe lambs is not accounted for by decreased ESR1 mRNA or protein in kisspeptin neurons. Endocrinology 159: 1-13. doi: 10.1210/en.2017-0059