Consumers consider tenderness and steak color to be two important attributes associated with meat quality. However, inconsistencies in both tenderness and steak color remain despite similar production practices of beef cattle. Stressful events before harvest may impact meat quality by initiating certain pathways such as abundance of heat shock proteins (HSP) and oxidation within the skeletal muscle. Heat shock proteins have been associated with tenderness while oxidation may affect steak color and flavor. In this study, 40 Holstein steers were administered adrenocorticotrophic hormone (ACTH) to mimic a stressful event before harvest. Animals were harvested at different times following the ACTH challenge (2 h, 12 h, 24 h, and 48 h; n=10). In addition, animals were grouped based on cortisol response 0.5 h after initiation of the ACTH challenge (lowest, lower, higher, and highest; n=10) because initial serum cortisol concentrations were variable following the challenge. Skeletal muscle tissues were collected from the longissimus lumborum (LL) before the ACTH challenge, at harvest, and after 14 d of aging. Blood samples were also collected. We investigated how time of harvest and cortisol response affected HSP abundance, tenderness, oxidation, and steak color. Time of harvest affected the relative abundance of one of three HSP analyzed, Phosphorylated-HSPβ1 (P-HSPβ1). The abundance of P-HSPβ1 was increased at harvest in animals harvested 48 h after the ACTH challenge, while after 14 d of aging animals that were harvested 24 h after the ACTH challenge had increased abundance of P-HSPβ1. Additionally, time of harvest affected tenderness assessed by the protein troponin I, a regulatory protein in the muscle, and myofibrillar fragmentation index (MFI). Animals that were harvested 24 h after the ACTH challenge had increased abundance of troponin at harvest and increased MFI after 14 d of aging. Both time of harvest and cortisol response affected oxidation assessed by DJ1, protein which is a marker of oxidation, and thiobarbituric acid reactive substances (TBARS). Animals that were harvested 24 h after the ACTH challenge had increased abundance of DJ1 and increased concentration of TBARS in the serum. In addition, steak color was affected by both time of harvest and cortisol response. Animals that were harvested 24 h and 48 h after the ACTH challenge had yellower and redder steaks than animals harvested 2 h and 12 h after the challenge. These finding indicate that time of harvest and cortisol response following a stressful event impacts meat quality, however more research is needed to fully understand the impacts of premortem stress on meat quality
