Impact of Stress on Tenderness in Red Branded Carcasses
The project funded a comprehensive analysis of blood collected at slaughter and tenderness measures for beef longissimus muscle steaks for over 400 head of cattle slaughtered at one of the major beef packing plants in Ontario. Blood was collected at slaughter from steers and heifers on 8 different slaughter days over a 3 month period with the blood analyzed for lactic acid concentrations, 2 major indicators of stress, cortisol and creatine kinase, and a comprehensive metabolic profile (urea, glucose, major electrolytes, major blood proteins, cholesterol, betahydroxybutyrate, nonesterfied fatty acids). Grade information was collected for each animal. A whole strip loin was obtained for each head of cattle and transported to the University of Guelph Meat Laboratory where steaks were aged for 3, 7, 14, 21, and 28 days. The steaks were assessed for tenderness based on the Warner Bratzler shear force protocol. Rates of postmortem tenderization were determined for each animal. Pearson correlation coefficients were determined across all measures of tenderness and blood measures. Our hypothesis was that assessment of blood lactates levels at slaughter could be used to determine stress in cattle and may be used to predict ultimate beef tenderness. Since the technology to determine blood lactate levels is available in a hand-held meter, this could be incorporated in sensors for on line determination of stress in cattle at slaughter. Major plants could incorporate technology to measure blood lactate levels right at sticking (exsanguination, the primary cause for death of animals at packing plants) and then segregate beef carcasses based on carcasses likely to produce tender beef and carcasses that would require postmorterm tenderization procedures to ensure adequate tenderness. The current study found a significant relationship between blood lactate levels at slaughter and cortisol levels of blood with cortisol being a major stress hormone. The study did not find any relationships between tenderness measures and rates of postmortem tenderization with the major blood metabolites determined in the study including lactate, cortisol, and creatine kinase. The results are disappointing due to the potential to incorporate on-line technology to predict tenderness right at death and to identify carcasses that need extensive postmorterm processing. This is also disappointing as a more positive relationship between tenderness and blood lactate concentrations may have encouraged the major packing plants to examine lot to lot differences in blood lactate levels at slaughter. This procedure could be used to identify the cause of the stress for given lots of cattle, i.e. is it due to management practices at the feedlot, the transport of cattle from the feedlot to the packing plant, and(or) unloading, holding, and processing practices at the packing plant.
The immediate outcome of this study is that no relationship existed between tenderness measures and rates of postmortem tenderization with the major blood metabolites determined in the study including lactate, cortisol, and creatine kinase. Based on past studies in the last 10 years, there was promise that these relationships existed which could be used to not only improve the beef eating experience for consumers in regards to tenderness but also to improve animal welfare. The study did find that blood lactate levels at slaughter were positively correlated with blood cortisol levels, a major indicator of stress. This provides the opportunity for further work in this area from an animal welfare basis as there is scope for rapid on-line determination of blood lactate levels at slaughter. There may be value also from a meat quality basis in regards to product shelf-life and the other major palatability attributes of beef, juiciness and beef flavor.
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