264 Precision feeding for programming brain development and reproductive performance of beef heifers.

Abstract Approximately 5 million beef heifers enter the U.S. cow herd annually, and their lifetime productivity is largely dependent upon their ability to attain puberty and produce a calf by 24 mo of age. However, a considerable proportion of heifers within existing U.S. production systems fail to achieve these goals, particularly in southern regions where Bos indicus-influenced cattle predominate. Consequently, managerial approaches are needed that employ precision feeding to program the reproductive neuroendocrine axis, while minimizing feeding costs and optimizing the consistent attainment of puberty by approximately 14 mo of age. Our previous research has clearly demonstrated that increased BW gain between 4 and 8 mo of age facilitates pubertal development by programming hypothalamic centers that regulate gonadotropin releasing-hormone (GnRH) secretion. Among the different metabolic hormones, leptin plays a critical role in conveying nutritional information to the hypothalamus and controlling puberty. Two hypothalamic neuronal populations that express the orexigenic peptide neuropeptide Y (NPY) and the anorexigenic peptide alpha melanocyte-stimulating hormone (αMSH; a product of the POMC gene) are key components of afferent pathways that convey inhibitory (NPY) and excitatory (αMSH) inputs to GnRH and kisspeptin neurons. Our studies have demonstrated that short-term increases in dietary energy intake after early weaning at 4 mo of age result in epigenetic, structural, and functional modifications in these hypothalamic pathways to promote high-frequency, episodic release of GnRH and luteinizing hormone. However, integrating the foundational knowledge of metabolic imprinting of the brain for early puberty with issues related to lifetime performance is complex. One approach has been to employ a novel stair-step precision feeding regimen involving alternating periods of dietary energy-restriction and re-feeding during juvenile development. This approach is designed to support early onset of puberty by imprinting functional alterations in the hypothalamus during key periods of brain development while optimizing other aspects of growth and performance. Finally, while several key processes of fetal brain development occur during late gestation, neither maternal undernutrition (BCS 3.0-3.5) nor maternal obesity (BCS 7.5-8.0) during the last two trimesters of gestation impacted the organization of hypothalamic neurocircuitries controlling GnRH/LH secretion or age at puberty in the heifer offspring. Collectively, these results indicate that the adult reproductive phenotype in Bos indicus-influenced females is resilient to significant degrees of nutritional stress imposed during prenatal development, particularly if early gestation (first trimester) is avoided. These findings are in contrast with reports in Bos taurus females in which late gestation nutritional extremes result in delayed puberty in heifer offspring, suggesting that potential genotype-specific differences may exist. Research support: USDA-NIFA-AFRI (2018-67015-27595 and 2021-67015-33676).