Impacts of Exposure to a High Concentrate Based Diet on Marbling Development in Beef Cattle

The value of a carcass is largely dependent on lipid deposition. The subcutaneous and visceral depots are often reported to develop and fill first. These depots also have little to no value, and often result in carcass price discounts. The intramuscular depot is well correlated with consumer palatability and carcass value. The ability to increase deposition of intramuscular lipid while minimizing the filling of low value fat depots provides ample opportunity to improve carcass value. Three studies were performed to investigate the ability to improve marbling deposition by altering the timing and duration of exposure to high concentrate diets. The first study reported the impacts of a high concentrate diet compared to grazing high quality forages during the first 100 d post-weaning or during the finishing period (218 d post-weaning to harvest). Results suggested that feeding a high concentrate diet immediately post-weaning improves marbling deposition similarly to consuming high concentrate diet during the finishing phase. Additionally, subcutaneous tissue of steers consuming high concentrates during finishing had upregulated levels of lipogenic gene mRNA compared to grazing forages; whereas the study was not well designed to study the impacts of diet during phase on gene expression. Therefore, the second study investigated the impacts of a high concentrate diet or grazing high quality forages during the first 127 d post-weaning. Steers consuming a high concentrate diet had greater ADG and final BW compared to steers grazing forages. Additionally, HCW, LM area, 12th-rib fat thickness, and marbling score were greater in concentrate fed steers. Gene expression levels in study 2 were similar in magnitude of change for concentrate fed steers compared to pasture suggesting that message level responds rapidly to dietary changes. Furthermore, glucose and insulin concentrations were correlated to marbling score suggesting a link between improved marbling deposition and insulin resistance. The third study was developed to investigate this hypothesis and included feeding a high concentrate diet for 0-, 40-, 80-, or 120-d prior to pasture finishing and included muscle biopsies and intravenous glucose tolerance tests to investigate the impacts of diet on insulin resistance and marbling deposition. Time on feed linearly increased carcass traits including marbling deposition. However, the glucose and insulin response was limited in magnitude compared to previous studies. The lack of change observed during the IVGTT may be related to the lack of difference across treatments for carcass characteristics. This dissertation provides evidence of improved marbling deposition based on early exposure to high concentrate diets. Further studies are warranted to continue investigation into the correlation between intramuscular lipid and insulin resistance