PSIII-24 Skeletal muscle antioxidant activity increases over time in beef steers and is greater in Angus compared with Brahman

Various managerial, nutritional, and environmental stressors may cause excessive production of reactive oxygen species (ROS) or free radicals which can damage cells and tissues, referred to as oxidative stress. Oxidative stress may impair beef cattle growth performance and product quality. Antioxidant enzymes are important in mitigating increased ROS to prevent oxidative stress, yet little is known about skeletal muscle antioxidant status in beef cattle of different breeds, ages and temperaments. We aimed to test the hypotheses that activities of antioxidant enzymes, glutathione peroxidase (GPx) and superoxide dismutase (SOD), in skeletal muscle would be greater in 1) Angus compared with Brahman steers; 2) longissimus thoracis (LT) compared with trapezius (TRAP) muscles; and 3) calm compared with temperamental animals. Brahman and Angus steers were classified as either calm (n = 13 Angus, n = 12 Brahman), intermediate (n = 11 Angus, n = 10 Brahman), or temperamental (n = 12 Angus, n = 12 Brahman) based on their pen score and exit velocity at weaning. Samples were collected from the LT and TRAP muscles of the steers at 10, 13, and 18 mo of age. Commercial assay kits were used to determine muscle GPx and SOD activities (Cayman Chemical, Ann Arbor, MI). Data were analyzed using linear models in SAS v9.4 with breed, age, temperament, breed × temperament, breed × muscle, and breed × age as fixed effects. Age was included as a repeated effect with animal within breed as the subject. Across muscle groups, Angus had greater GPx and SOD activities than Brahman (P < 0.0001). Additionally, GPx activity increased in both Angus and Brahman steers from 10 to 18 mo (P < 0.0001). In both breeds, the TRAP muscle had greater GPx activity than LT muscle (P < 0.0001). Brahman TRAP muscle also had greater SOD activity than Brahman LT muscle (P < 0.0001) but SOD activity was similar between muscle groups in Angus steers. Neither GPx nor SOD activity differed by temperament group in either breed or muscle group. These data suggest differences in skeletal muscle antioxidant status between Angus and Brahman steers which may mitigate oxidative stress, impacting growth performance as well as product quality at harvest.