Pre-slaughter stress arising from on-farm handling and its interactions with electrical stimulation on tenderness of lambs

The effect of electrical stimulation of lamb carcasses (n = 269) or its absence (n = 257) on shear force of m. longissimus thoracis et lumborum (LT) was monitored during ageing in pasture-fed merino lambs (n = 526). The lambs were slaughtered on four different days allowing durations of between one to 10 days of recovery from pre-slaughter handling (yarding, weighing and crutching) that affected ultimate pH (pHu). The right LT was removed 20–40 min post-slaughter, tightly-wrapped in cling film (prevents the muscle cross-section increasing and thus minimising shortening) and rapidly cooled to 15 °C to enter rigor mortis and age. At 0, 4, 24 and 72 h post-slaughter, pH measurements and samples for shear force measurement were taken. Pre-slaughter handling had a significant negative effect on pHu and several days recovery were required for pHu to reach values associated with optimal meat quality as reflected by pHu. Lambs with one and three days recovery (no significant difference between them) had a pHu > 5.7 in 50% of the muscles and 19.4% > pHu 5.8. Whereas, in lambs with 8–10 days recovery (no significant difference between them), only 8% had a pHu > 5.7 and 3.1% > pHu 5.8. each slaughter day electrically stimulated lambs were always more tender than non-stimulated lambs. For non-stimulated muscles at 72 h, shear force values >40 N occurred for 11.2% of the muscles: for electrically stimulated muscles at 72 h, shear force values >40 N occurred for 1.9% of the muscles. The rates of tenderisation were slower for intermediate pHu values resulting in higher shear force values at all ageing durations. With ageing at 72 h for intermediate pHu, non-stimulated muscles (n = 38) 17.64% were >40 N and for stimulated muscles (n = 34), 7.9% were >40 N.