Growth is frequently described as weight gain over time. Researchers have used this information in equations to predict carcass composition and estimate fat deposition. Diet, species, breed, and gender all influence fat deposition. Alterations in diets result in changes in fat deposition as well as the fatty acid profile of meat. Additionally, the amount and composition of the fat can affect lipid stability and flavor development upon cooking. Fat functions not only as a storage of energy and contributor of flavor compounds, but also participates in signaling that affects many aspects of the physiological functions of the animal. Transcription factors that are upregulated in response to excess energy to be stored are an important avenue of research to improve the understanding of fat deposition and thus, the efficiency of production. Additionally, further study of the inflammation associated with increased fat depots may lead to a better understanding of finishing animals, production efficiency, and overall health.

Meat tenderness is a critical quality trait that varies even among carcasses of similar USDA quality grades. In this comparative study of beef cattle and sheep, we investigated how gene expression profiles in muscle and adipose tissues are associated with carcass quality grades and Fat Classes. Fifteen steers and fifteen wethers were raised to produce carcasses spanning Standard, Select, and Choice USDA quality grades (beef) or varying Fat Classes (sheep). In beef, higher quality grade was associated with significantly improved tenderness (lower shear force), while sheep tenderness did not differ consistently across Fat Classes. Exploratory RNA sequencing identified hundreds to thousands of differentially expressed genes (DEGs) between high- and low-quality or fatness groups, particularly in sheep muscle. DEGs were enriched in pathways related to muscle growth, lipid metabolism, and immune signaling. While these transcriptomic differences suggest biological processes associated with carcass traits, the findings are correlational, should be interpreted as hypothesis-generating, and require further validation in larger independent populations. These exploratory findings suggest species-specific differences in the relationship between fatness and tenderness and identify candidate molecular pathways for future investigation.