# Effects of Premortem Stress on Protein Expression, Steak Color, Oxidation, and Myofibrillar Fragmentation Index in the Longissimus Lumborum

## TL;DR

This study shows that stress before slaughter affects beef quality by changing protein levels, steak color, and meat texture.

## Contribution

The study reveals how premortem stress impacts specific proteins and meat quality metrics in beef.

## Key findings

- Premortem stress alters the expression of proteins like SHSPs, DJ-1, and troponin in beef.
- Stress before slaughter influences steak color and myofibrillar fragmentation index.
- Harvest time after stress affects meat pH and blood cell counts.

## Abstract

This study aimed to determine the effects of premortem stress on beef quality following harvest. Forty castrated Holstein calves underwent an adrenocorticotropic hormone (ACTH) challenge to emulate a stress response. The calves were harvested at different times (2, 12, 24, and 48 h) following the challenge. In addition, cortisol was measured to determine the specific stress response of each animal during the ACTH challenge. Beef quality attributes such as the breakdown of myofibrillar proteins, color, and pH were analyzed in samples at different ages following harvest. The results show that harvest time following the ACTH challenge does impact the quality of beef that is produced. Additionally, steak color, tenderness, and protein expression may be related to stress that occurs prior to harvest.

Forty castrated Holstein calves underwent an adrenocorticotropic hormone (ACTH) challenge to assess the effects of premortem stress on the longissimus lumborum (LL) following harvest. LL biopsies were collected before the challenge, at different harvest times (2, 12, 24, and 48 h; n = 10), and after 14 d aging. The expression of small heat shock proteins (SHSPs), deglycase 1 (DJ-1), and troponin were analyzed. Blood was analyzed throughout the ACTH challenge and at harvest for cortisol, oxidative stress, and complete blood count (CBC). Color and myofibrillar fragmentation index (MFI) were measured in aged samples. Unexpectedly, calves from different harvest times differed (p = 0.05) in cortisol response. Calves were divided into two different cortisol response groups (high or low; n = 20). Statistical analysis assessed the effects of cortisol response (n = 20), harvest time (n = 10), and their interaction. Harvest time altered SHSPs (p = 0.03), DJ-1 (p = 0.002), and troponin (p = 0.02) expression. Harvest time and cortisol response impacted steak color (p < 0.05), and harvest time altered steak pH (p < 0.0001). Additionally, various CBCs were changed (p < 0.05) by harvest time. Harvest time changed (p = 0.02) MFI. These data demonstrate that the protein expression, color, and MFI of the LL may be influenced by premortem stress.