The eating quality of meat of steers fed grass and/or concentrates

Abstract

The objective was to determine, relative to animals expressing their full potential for carcass growth, the impact on meat quality of increasing carcass growth of grazing steers by supplementing with concentrates or by increasing grass supply. Sixty-six continental (Limousin and Charolais) crossbred steers (567 kg) were assigned to one of six diets: (1) 18 kg grass dry matter (DM); (2) 18 kg grass DM grass and 2.5 kg concentrate; (3) 18 kg grass DM and 5 kg concentrate; (4) 6 kg grass DM and 5 kg concentrate; (5) 12 kg grass DM and 2.5 kg concentrate; or (6) concentrates daily. Animals were slaughtered after an average of 95 days. Samples of the M. longissmus dorsi (LD) were collected at the 8–9th rib interface and subjected to sensory analysis and to other assessments of quality following 2, 7, or 14 days aging. Carcass weight gain averaged 360, 631, 727, 617, 551 and 809 g/day for treatments 1 to 6, respectively. There was no difference between diets for colour, Warner–Bratzler shear force (WBSF) or any sensory attribute of the LD. WBSF was negatively correlated with (P<0.05) carcass growth rate (−0.31) but only a small proportion of the variation in meat quality between animals could be attributed to diet pre-slaughter or carcass fatness. It is concluded that high carcass growth can be achieved on a grass-based diet without a deleterious effect on meat quality.

Introduction

Feed costs are a major proportion of total variable costs in most beef systems and efficiently managed grazed grass can be the cheapest feedstuff in temperate climates (O'Riordan & O'Kiely, 1996). The value of beef from grass-finished cattle is often discounted compared with concentrate-fed beef because of perceived differences in tenderness (Chrystall, 1994), colour (Baardseth, Skrede, Naes, Thomassen, Iversen, & Kaaber, 1988), juiciness (Hutchings & Illford, 1988) and flavour (Melton, 1990). There is evidence, particularly from North American beef production systems, that concentrate-fed animals produce more tender and better-flavored meat than forage-fed animals (Larick et al., 1987, Medeiros et al., 1987). However, in many of these experiments, dietary effects were confounded by differences in animal age, pre-slaughter growth rate or carcass weight/fatness at slaughter (e.g. Bowling et al., 1978, Harrison et al., 1978) factors that influence meat quality, in particular tenderness and flavour (Spanier, McMillian, & Miller, 1990). French et al. (2000a) showed that when steers had a similar mean rate of carcass growth, pre-slaughter diet per se (autumn grazed grass, concentrates or grass silage) did not affect the sensory perception of meat quality. In that study, the rate of carcass growth was restricted to that of animals fed unsupplemented grass and was less than the genetic potential of the animals used. To maximise profitability, the growth potential of the animals should be achieved with maximum inclusion of grazed grass but without an impairment of sensory quality. We hypothesised that inclusion of grass in high-energy finishing diets for beef cattle would have little effect on meat quality.

The objective of this study therefore, was to measure the quality of meat from cattle finished on grass alone, on concentrates offered ad libitum (expressing full genetic potential for growth) or on various combinations of both.