Relationships of behavioral and physiological symptoms of preslaughter stress to beef longissimus muscle tenderness1

Relationships between behavioral and physiological symptoms of preslaughter stress and LM Warner-Bratzler shear force (WBSF) were investigated using Bos taurus steers (n = 79) and heifers (n = 77). Measurements of heart rate, respiration rate, rectal temperature, and concentrations of serum cortisol and plasma epinephrine were used as indicators of stress associated with physical handling and chute restraint, whereas concentrations of cortisol, glucose, lactate, and creatine kinase in blood samples obtained at exsanguination were measured to reflect physiological reactions of animals to transportation stress. Increased plasma epinephrine concentration, indicative of acute handling stress, was associated with elevated heart rate (r = 0.42, P 0.05) among behavior categories. Grouping cattle according to differences in plasma lactate concentration categorized them according to mean differences in LM WBSF. Moreover, steaks from cattle with the greatest plasma lactate concentrations at slaughter (91st to 100th percentile) had a delayed response to aging that persisted until 14 d postmortem. Stress-induced differences in LM tenderness observed in this study were independent of differences in muscle pH.