PROTEIN SUPPLEMENTS & MUSCLE GROWTH

Protein Supplements & Muscle Growth

Abstract

Protein supplements and a magnesium bolus and were used in lambs in a 2×2 factorial design to investigate the effect on growth? preslaughter stress measurements? muscle glycogen? and meat quality. In total? 64 Perendale lambs were used (32.7±0.53 kg? mean±SEM). Feed supplemented animals received 150 g feed pellets day-1 in addition to pasture grazing? and this increased growth from 183 to 207 g day-1. Mean delivery of Mg from the boluses was 0.17 g day-1 for 28 days? with no effect on growth rates? or any other of the variables measured. Urinary noradrenaline? adrenaline and cortisol did not differ between groups in the immediate pre-slaughter period. The meat ultimate pH was not different between groups and had a mean range of 5.47-5.53. Muscle residual glycogen did not differ between groups and had a mean range of 42-43 mmol kg-1. Finally there were no differences in shear force values at all ageing times. The final shear force value of 2.5 kg F after 72 h ageing at 15 °C was a low value representing tender meat. These studies indicate that if nutrition is adequate and stress levels are low? there are no differences in meat tenderness of pasture fed lambs compared with those having feed supplements to increase growth rate.

Protein Supplements & Muscle Growth

1. Introduction

Muscle glycogen levels at slaughter for domestic meat producing animals must be sufficient for muscle pH to decrease to approximately 5.5 postmortem to allow optimal tenderization during ageing (Purchas and Warriss). In New Zealand? lambs are usually raised on pasture and a significant number have a sub-optimal meat pH of 5.8 or greater ( Graafhuis & Devine? 1993). Two major reasons for sub-optimal glycogen levels at slaughter are: excessive glycogen losses from stress during transport and lairage ( Jones & Tong? 1989) and a poor protein plane on-farm ( Pethick & Rowe? 1996). The importance of on-farm nutrition must be emphasized? as evidence is growing that levels of muscle glycogen increase with metabolisable energy intake ( Pethick et al.? 2000). Reserves of these glycogen stores can then act as a buffer in the preslaughter period. Pastoral lambs are often raised without supplemental feeding? and if supplements are provided? it is often only at a maintenance level.

In addition to feed supplements for growth promotion? magnesium (Mg) supplementation has shown improvements in meat quality and a reduction in the incidence of PSE in pork (D; D and D). Similar benefits have been demonstrated in lamb with improved meat quality? and increased residual glycogen postmortem (Gardner and Pethick)? although in one study Mg supplementation may have caused toughening of meat ( Apple? Watson? Coffey? Kegley? & Rakes? 2000).

The aim of this study was to investigate the effect on lambs of supplementary feeding and Mg on growth rates? stress responses at slaughter? muscle glycogen and meat tenderness in pastoral lambs. We investigated the effects of using a feed supplement and Mg bolus in a 2×2 factorial ...