425 Effects of pre-mortem stress on protein expression, steak color, and myofibrillar fragmentation index in the longissimus lumborum following harvest

<jats:title>Abstract</jats:title><br> <jats:p>Undesirable variation in beef tenderness and stability of flavor and color may be associated with the abundance of heat shock proteins (HSP). This study aimed to determine whether pre-mortem stress impacts HSP expression in the skeletal muscle following harvest. Forty Holstein steers were administered an i.v. bolus dose of adrenocorticotropic hormone (ACTH; 0.1 IU/Kg BW) to mimic an acute pre-mortem stress. Longissimus lumborum (LD) biopsy samples were taken prior to the ACTH challenge. Serum cortisol was measured every 0.5 h from -2 to 6 h relative to the ACTH challenge. Skeletal muscle and blood samples from 10 steers were collected at each harvest timepoint at (2, 12, 24 and 48 h post-challenge). Samples were collected from the LD immediately after harvest and after 14 d of aging. Protein expression of HSPβ1, P-HSPβ1, HSPβ5, and DJ-1 was analyzed in muscle samples taken prior to the ACTH challenge, at harvest, and after 14