Beef carcass value is influenced by the quantity and distribution of adipose
tissue. Elucidation of metabolic controls of caloric partitioning between adipose depots
could lead to development of production solutions that enhance beef carcass value.
Historical trends in Choice and Select beef supply and short-term demand structures for
Choice and Select boxed beef were explored. Recent stabilization in slaughter mix may
suggest an optimum is being approached. Evaluation of short-run demand supports this
premise, and suggests that Choice and Select products may not be strong substitutes.
Growth-based prediction equations relating carcass traits to growth traits using
ultrasound measurements as the basis of projections under different growing systems
were explored. Accuracy of carcass fat predictions from growth-based equations is
influenced by weight gain between ultrasound and endpoint, breed, and gender; scans
out to 120 d pre-harvest may be accurate. Angus steers were used to test effects of
dietary energy source on muscle and adipose tissue metabolism and insulin sensitivity.
Results suggest that feeding hay limited both glucose supply and tissue capacity to increase glucose utilization in response to insulin without altering acetate conversion to
fatty acids. Because subcutaneous (s.c.) adipose tissue consistently utilized more acetate
and oxidized more glucose than intramuscular (i.m.), these results suggest that hay-based
diets may alter i.m. adipose tissue metabolism with less impact on s.c. adipose tissue.
Additionally, s.c. adipose tissue may become resistant to insulin in steers fed to an
excessive s.c. fat thickness. A final experiment was designed to test the effects of dietary
energy source during backgrounding and compositional endpoint on adipose tissue
metabolism and insulin sensitivity. Feeding hay during backgrounding may have
differential effects on tissue lipogenesis. Feeding hay increased both glucose oxidation
and incorporation of acetate into fatty acids; in i.m. insulin failed to stimulate glucose
conversion to lipid. As physiological maturity increases, glucose conversion to CO2 and
lactate increased, but the ability of insulin to stimulate lipid synthesis from glucose may
be reduced. These data provide foundation for a hypothesis regarding diet-mediated
regulation of differential adipose tissue metabolism. Validation of these hypotheses
could generate nutritional strategies that alter the rate and site of adipose deposition.
- Sawyer, Jason Associate Professor and Associate Department Head