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

Abstract 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 (pH u ). 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 pH u and several days recovery were required for pH u to reach values associated with optimal meat quality as reflected by pH u . Lambs with one and three days recovery (no significant difference between them) had a pH u  > 5.7 in 50% of the muscles and 19.4% > pH u 5.8. Whereas, in lambs with 8–10 days recovery (no significant difference between them), only 8% had a pH u  > 5.7 and 3.1% > pH u 5.8. Within 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 pH u values resulting in higher shear force values at all ageing durations. With ageing at 72 h for intermediate pH u , non-stimulated muscles ( n  = 38) 17.64% were >40 N and for stimulated muscles ( n  = 34), 7.9% were >40 N.