The metabolism of glycogen and ultimate pH of muscle in Merino, 1st cross and 2nd cross wether lambs as affected by stress at slaughter.

Abstract

The metabolism of glycogen and ultimate pH of muscle in Merino, 1st cross and 2nd cross wether lambs as affected by stress at slaughter G.E. Gardner , L. Kennedy , J.W. Milton and D.W. Pethick `School of Veterinary Studies, Murdoch University, Murdoch WA 6150 *Faculty of Agriculture I University of Western Australia, Nedlands WA 6009 1 1 2 1 There is an industry perception that Merino lambs yield darker meat compared to cross bred lambs. However, the role of breed and the interactions with nutrition and stress have not been studied. The aim of this experiment was to compare the metabolism of muscle glycogen and ultimate pH (pHu) of muscle in Merino and cross bred lambs fed the same diet and receiving different levels of stress pre-slaughter. Twenty five Merino, 24 1st cross (Merino dam and Poll Dorset sire( 1X)) and 23 2nd cross (Border Leicester x Merino dam and Poll Dorset sire (2X)) lambs (6 months old and 30kg liveweight) were in pens of 7-9 animals, with 3 pens/breed. For 8 weeks the lambs were fed 1.3kg/ d of a ration consisting of 30% lupin 29.65% cereal straw, 28% barley grain, 8% canola meal, 2% limestone, 1.35% mineral/vitaminmix, 0.5% salt, 0.5% gypsum and 1OOgm Rumensin/tonne (ME 10.8MJ/kg DM, protein 17.4% DM). At week 6, a muscle biopsy was taken Corn 5 lambs in each pen. At week 8,5 animals from each breed were slaughtered at an experimental abattoir 10 minutes after removal from their pens (low stress slaughter). The remaining lambs, kept in separate breed groups, were transported for 2 hours and slaughtered after 24 hours lairage at a commercial abattoir. Muscle samples taken by biopsy and at slaughter were assayed for glycogen (corrected for lactate concentration). The pHu of muscle was measured 48 hours post slaughter. Muscle tissues of lambs undergoing the low stress slaughter had higher post mortem muscle glycogen concentrations, lower pHu and no significant loss of glycogen between pen and slaughter. Breed had no effect on any of the parameters measured under low stress slaughter conditions, or at the muscle biopsy. In contrast, under commercial slaughter conditions, the muscle of Merino lambs had the lowest post mortem glycogen concentration, the highest pHu and greatest loss of glycogen between pen and slaughter. We conclude that an increasing proportion of Merino genetics is associated with a greater sensitivity to stress in lambs destined for slaughter. Table 1 Glycogen concentration (% w/w) and pHu of muscle in Merino and cross bred sheep. Recent Advances in Animal Nutrition in Australia 1997 University of New England, Armidale NSW 2351, Australia