Relationship between pre-slaughter stress responsiveness and beef quality in three cattle breeds

Abstract

The relationship between stress responsiveness and beef quality of 40 Nguni, 30 Bonsmara and 30 Angus steers was determined. The L^∗ values, pHu, cooking loss (CL) and Warner-Bratzler shear force (WBSF) were determined. Catecholamine levels were determined from urine samples collected at slaughter. Bonsmara steers had the highest (P < 0.05) levels of catecholamines with respective epinephrine, norepinephrine and dopamine concentrations of 10.8, 9.7 and 14.8 nmol/mmol. Nguni steers had the lowest (P < 0.05) levels of catecholamines, with respective catecholamine concentrations of 5.1, 4.3 and 4.0 nmol/mmol. In the Nguni steers, there were significant (P < 0.05) correlations between catecholamines and L^∗ and between dopamine and tenderness in meat aged for two days (WBSF2). In the Bonsmara, dopamine was correlated (P < 0.05) pHu, WBSF2 and CL. No significant correlations were found in the Angus. Therefore the relationship between stress responsiveness and certain beef quality traits may not be similar in different breeds.

Introduction

Pre-slaughter glycogen depletion in muscle may result in meat with a higher ultimate pH (pHu) (Kannan, Chawan, Kouakou, & Gelaye, 2002), which is not always ideal for conversion of muscle to meat (Purchas, Yan, & Hartly, 1999). Beef with pHu values higher than 6.0 is undesirable because of its dark colour (Bartos et al., 1993, Kreikemeier et al., 1998, Mounier et al., 2006), high variation in tenderness (Silva, Patarata, & Martins, 1999), increased water holding capacity (Apple et al., 2005, Zhang et al., 2005) and poor palatability (Viljoen et al., 2002, Wulf et al., 2002). High pH also promotes growth of microorganisms which lead to the development of off-odours, and often slime formation (Gallo et al., 2003, Gardner et al., 2001). It is important to determine the factors which affect the depletion of glycogen levels and the mechanism by which this occurs. Breed (King et al., 2006), feeding management, nutritional status (Andersen et al., 2005, Sañudo et al., 2004, Wheeler et al., 1996), loading and transportation (Schaefer et al., 1997, Mota-Rojas et al., 2006), temperament (King et al., 2006), pre-slaughter stress and how the animals physiologically respond to stress (O’Neill, Webb, Frylinck, & Strydom, 2006) are factors that affect glycogen depletion in animals and meat quality parameters such as pHu, colour, cooking losses and tenderness.

Animals waiting for slaughter can be stressed by factors such as restraint, handling, novelty of the pre-slaughter environment, adverse weather conditions, hunger, thirst and fatigue (Apple et al., 2005, Fazio and Ferlazzo, 2003, Grandin, 1997, Mormède et al., 2002). Catecholamines have been shown to cause depletion in muscle glycogen in the pre-slaughter period (O’Neill et al., 2006, Tarrant, 1989). Dopamine plays a part in the control of cortisol secretion and glycogen metabolism (Ahmadzadeh, Barnes, Gwazdauskas, & Akers, 2006).

The concentrations of these hormones are the result of neuronal washout from tissues with sympathetic nerves and are therefore important indicators of sympathetic nervous system activity (Young, Rosa, & Landsberg, 1984). Use of urinary stress hormones in assessing stress responsiveness is reliable because their measurement is non-invasive and their levels in urine are not affected by the massive release of catecholamines and dopamine associated with slaughter because there is a delay between elevation of their concentration in plasma and subsequent elevation in the urine (Hay et al., 2000, Lay et al., 1992).

When an animal is stressed in the pre-slaughter environment, there is a rapid release of catecholamines which result in glycogen depletion (Lacourt & Tarrant, 1985) causing high pHu and darker meat. Although Muchenje, Dzama, Chimonyo, Raats, and Strydom (2008) reported lower L^∗ values in meat from Nguni steers than that of Bonsmara and Angus steers, they did not report pHu differences among the three breeds. The differences in L^∗ values could not be full understood, although O’Neill et al. (2006) postulated that the differences could have been due to the Nguni releasing more catecholamines than the other breeds. While Foury et al. (2005) quantified relationships between stress responsiveness and hormones in pigs, most reports on stress responsiveness and meat quality are largely speculative and do not quantify the magnitude of the relationship between stress hormone levels and meat quality (Mota-Rojas et al., 2006, O’Neill et al., 2006, van Schalkwyk et al., 2000).

There is, therefore, need to evaluate the relationship between stress responsiveness and meat quality of Nguni, Bonsmara and Angus cattle raised under conditions that mimic rural conditions and management systems. The objective of the current study was to determine the relationship between stress responsiveness and meat quality characteristics of Nguni, Bonsmara and Angus when raised on natural pasture. The null hypothesis tested was that, under natural grazing, the relationship between stress responsiveness and the quality of meat from Nguni, Bonsmara and Angus breeds is similar.