The effect of nutritional supplements on growth rate, stress responsiveness, muscle glycogen and meat tenderness in pastoral lambs.

Nutritional 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.