Abstract
Beef cattle are primarily raised for meat production, which feeds consumers worldwide making them an important species for food sustainability. Research in beef cattle physiology is important to support and understand how to promote healthy growth and development of our livestock which supports animal health and welfare, producer economic viability, and food security. Furthermore, with rapid advancement of genetics and genomics it is important that phenotypes such as growth are better characterized with respect to physiological regulation. Proper bone and muscle growth in cattle are crucial for animal health and wellbeing, and this dissertation is comprised of work with both tissues. The first study in this dissertation revealed genetic variants that are associated with the phenotype of advanced skeletal maturity in chronologically young heifers, and it was further observed that FDA approved, commercial high estrogenic implants promote advanced bone ossification in genetically predisposed commercial cattle. Identifying these variants associated with bone ossification in early heifer skeletal development provides insight on early maturation in beef females and is critical towards opportunities for applied methods of improvement. These SNPs could be further evaluated for possible links to precocious puberty as bone development occurs with sexual maturity. The two subsequent studies of this dissertation focused on proteins that are released from muscle cells and have been shown to regulate muscle growth in human and biomedical species, but many have not been evaluated in cattle. These were in vitro studies that utilized primary bovine satellite cells (BSC) to identify if undifferentiated and differentiated cells express genes that encode myokine proteins, as well as secrete the proteins. The target genes that were expressed included SPARC, FGF-21, MSTN, DCN, IL-6, IL-15, ERFE, FNDC5, and BDNF. The proteins SPARC, FGF-21, DCN, IL-6, IL-15, ERFE, and BDNF were expressed , which is suggestive of their role as myokines produced by BSC. The final study in this dissertation was another in vitro study to evaluate the same myokines when BSC are treated with ractopamine HCl, a beta-agonist, which is an approved growth promotant used to increase cattle lean muscle growth efficiency prior to harvest. Myokines have shown in other species to have a role in proper muscle development, increase muscle growth, muscle repair, and contribute to whole body health. The research herein helps contribute to assessment of physiological control of growth and development of beef cattle, increased growth efficiency, linking muscle growth phenotypes to genotypes, and overall animal health and wellbeing. This dissertation contributes to understanding of the physiology of bone and muscle growth, which will inevitably help support beef cattle growth and health, producer economic viability, and consumer sustainability into the future.