Evaluation of the relationship between animal temperament and stress responsiveness to M. longissimus lumborum tenderness in feedlot cattle

Temperament effects on meat quality were investigated using three contemporary groups consisting of Bonsmara-sired yearling-fed (n = 31), Angus-sired calf-fed (n = 49), and Angus-sired yearling-fed (n = 48) steers. To evaluate temperament, exit velocity, pen scores, and chute scores were determined before shipment to the feedlot, and exit velocity was measured on arrival to the feedlot and after approximately 70 d on feed. Serum cortisol concentration was determined at each evaluation and before slaughter. At slaughter, pH and temperature were monitored in the M. longissimus lumborum. USDA yield and quality grade factors and CIE color space values were determined, and M. longissimus lumborum steaks were evaluated for sarcomere length, 72-h calpastatin activity, proximate composition, and Warner-Bratzler shear force (WBS) values 3, 7, 14, and 21 d postmortem. Temperament categories were based on rankings within contemporary groups at each evaluation. Temperament traits were consistent across evaluations, and values decreased (P < 0.05) in magnitude over time. Relationships between temperament traits were consistent across contemporary groups. Increasing excitability was associated with higher (P < 0.05) serum cortisol concentration. Body weight was slightly lower (P < 0.05) in cattle with excitable temperaments at all evaluations. Carcass characteristics, proximate composition, muscle color, and calpastatin activity were unaffected by temperament. Carcasses from cattle with calm temperaments had higher 0.5 h postmortem pH values than those from intermediate and excitable cattle (0.1 and 0.2 units, respectively). The Angus-sired yearling-fed steers classified as Excitable had higher (P < 0.05) WBS values than the calmer Angus-sired, yearling-fed steers. This trend was observed in the Bonsmara-sired steers, although the values were not statistically different. No differences attributable to temperament were apparent in the Angus-sired calf-fed steers. Correlations were highest between temperament values and tenderness after 21 d. Yearling-fed cattle classified as Excitable before shipment to the feedlot produced tougher (P < 0.05) steaks than those from calmer animals. At evaluations later in production, Calm steers produced tougher (P < 0.05) steaks. Tenderness did not differ across temperament categories in calf-fed steers regardless of sorting time. These data indicate temperament influences tenderness, though the mechanism is not clear.