Stress hormones, carcass composition and meat quality in Large White × Duroc pigs

Abstract

The levels of stress hormones, cortisol and catecholamines (adrenaline and noradrenaline), were measured in urine collected after slaughter from the bladder, in 309 pigs (females and castrated males) from an F2 intercross between the Large White and Duroc breeds to analyze the relationships between stress-responsive neuroendocrine systems, carcass composition and meat quality. Intramuscular fat content was measured from a biopsy sample taken at a live weight of 70 kg from the longissimus lumborum muscle, and carcass and meat quality traits were also collected. Carcass fat content was higher and estimated carcass lean meat content was lower with increasing urinary levels of cortisol and adrenaline (that are highly correlated with each other), but was not related to the levels of noradrenaline, showing that adrenal hormones favor the accretion of fat at the expense of muscle proteins, a typical physiological effect of cortisol. On the contrary, intramuscular fat levels were unrelated to either hormone level. Finally, muscle pH measured 24 h after death was positively correlated with catecholamine levels, an effect related to the catabolism of muscle glycogen by catecholamines released by preslaughter stress, which impairs post-mortem acidification of meat. These results show the importance of a control over stress neuroendocrine systems to increase pork production and product quality, and the value of the genetic approach to reach this goal.

Introduction

The two main stress-responsive neuroendocrine systems play a critical role in the regulation of energy fluxes. The hypothalamic–pituitary–adrenocortical (HPA) axis influences feeding behavior, pancreatic hormone secretion, energy expenditure and the protein/lipid balance (Dallman et al., 1993). Altogether, cortisol, the main active hormone of the axis, released by the adrenal cortex, favors the accretion of fat at the expense of proteins (Devenport, Knehans, Sundstrom, & Thomas, 1989). Indeed, pig breeds with a higher carcass content of fat like Meishan (Bidanel, Caritez, Gruand, & Legault, 1993) or Duroc (Smith & Pearson, 1986) also produce more cortisol (Bergeron et al., 1996, Désautés et al., 1997, Désautés et al., 1999, Hay and Mormède, 1998, Mormède et al., 2004, Weiler et al., 1998). On the other hand, catecholamines (adrenaline and noradrenaline) released by the sympathetic nervous system (SNS) increase the use of energy stores (glycogen and lipids; Scheurink & Steffens, 1990) and exert anabolic effects on protein metabolism (Navegantes, Migliorini, & Kettelhut, 2002). Sympathetic activation by stress before slaughter reduces muscle glycogen content and post-mortem acidification, leading to DFD-type meat (dark, firm and dry) (Fernandez & Tornberg, 1991). The present experiment was designed to study the relationships of stress hormones secretion, as measured by their content in urine collected after slaughter, with carcass composition and meat quality in a segregating (F2) cross between two contrasting breeds, the Large White and Duroc pigs.