Interpretive Summary: Feeding distillers grains to cattle may affect beef tenderness early postmortem.
By: Dr. Thomas Powell
Since the rapid expansion of the ethanol industry several years ago, much attention has been given to distillers grains as a livestock feedstuff. Ethanol production utilizes the starch in corn, leaving a higher concentration of protein and fat in the byproduct distillers grains. Researchers from the University of Nebraska in cooperation with Brazilian scientists recently published findings in the Journal of Animal Science that may point to a mechanism for the observed effect that diets with distillers grains can have on the tenderness of beef.
A total of 256 steers were fed for 134 days on either corn or one of three diets containing modified distillers grains plus solubles (MDGS): 40% full fat MDGS, 40% de-oiled MDGS, or 38% de-oiled MDGS plus 2% corn. The study looked at aging time and retail display as additional variables (2, 9, 16, or 21 days aging and 0 or 7 days retail display).
Samples were analyzed for sarcoplasmic reticulum (SR) membrane fatty acid composition, Warner–Bratzler shear force (WBSF), sarcomere length, and proteolysis early postmortem.
Typically, postmortem tenderness development can occur from the physical disruption of sarcomeres during rigor mortis or from enzymatic degradation of proteins. Results of this study show a trend towards increased tenderness early postmortem (2 d aging) from the cattle fed MDGS diets with a more pronounced difference in the de-oiled MDGS diets. The sarcomere length was not different between treatments, indicating that the observed change in tenderness was likely due to proteolysis and not rigor shortening.
Examining the remaining results provided some insight into the nature of the proteolysis differences in the samples. Early postmortem (2d) samples from cattle fed MDGS showed higher sarcoplasmic calcium concentration, which could trigger the observed proteolysis. MDGS increased linoleic acid and tended to increase PUFA in the SR membrane. The researchers speculated that these changes in the fatty acid composition of the SR membrane could be stimulating the calcium release mechanism in the SR. Alternatively, the altered fatty acid profile could make the SR membrane more prone to oxidation, resulting in disruption of the membrane and subsequent release of calcium.
Notably, the study also measured troponin-T degradation and found no differences between treatments, even where differences in tenderness were found. Previously published research suggested that degradation of troponin-T might be an accurate indicator of proteolysis and tenderization. The authors of this study conclude that that the degradation of a single regulatory protein will unlikely explain postmortem tenderization.
To view the full article, please visit the Journal of Animal Science.