Introduction The rate of muscle pH fall post-slaughter significantly affects lamb meat quality through its effects on time to rigor onset and the occurrence of cold-shortening (Chrystall and Devine 1985). Under conditions of rapid chilling, electrical stimulation of lamb carcasses is recommended to prevent muscles from cold-shortening and the associated increases in meat toughness (Chrystall and Devine 1985). Conversely, Marsh et al. (1987) reported that electrical stimulation increased meat toughness in beef carcasses, which exhibited rapid glycolysis post-slaughter. Pre-slaughter stress in pigs has also been clearly shown to increase the rate of pH fall post-slaughter, increase the incidence of pale, soft, exudative (PSE) meat (D’Souza et al. 1998a, 1998b) and decrease the tenderness of aged meat (Channon et al. 2000). Pale, soft, exudative beef muscle has recently been reported (Aalhus et al. 1998) but it has not been reported in lamb muscle. There is a perception that lamb carcasses are not susceptible to PSE. The effects of pre-slaughter stress on lamb meat quality are frequently attributed to an increased incidence of dark-cutting high pH meat that occurs when pre-slaughter stress causes muscle glycogen depletion (Eldridge 1989). Swim-washing of lambs and herding with dogs before slaughter increases the toughness of lamb meat relative to minimal stress, although the effect was not independent of increased ultimate pH (pH u ) (Geesink et al. 2001). In another study, Daly et al. (1995) reported that 20 min of exercise stress pre-slaughter increased toughness in electrically stimulated lamb meat. They postulated that events specifically associated with muscular activity may affect the tenderness of the meat independent of post- slaughter pH fall. However, these studies did not include measures of protein denaturation or water-holding capacity (WHC) and it is proposed that the loss of tenderness caused by acute pre-slaughter exercise may be the result of denaturation of proteases pre-slaughter or early post mortem. It is also proposed that acute pre-slaughter stress of lambs will result in a loss in the WHC of the muscle, and any loss in WHC is economically important to an industry that primarily trades on weight. The aim of the current experiment was to investigate whether the combination of acute pre-slaughter stress and electrical stimulation would increase toughness and reduce the WHC in lamb meat. Australian Journal of Experimental Agriculture, 2005, 45, 553–560 0816-1089/05/050553 10.1071/EA03270 © CSIRO 2005 R. D. Warner A,C , D. M. Ferguson B , M. B. McDonagh A , H. A. Channon A , J. J. Cottrell A and F. R. Dunshea A A Department of Primary Industries, 600 Sneydes Road, Werribee, Vic. 3030, Australia. B CSIRO Livestock Industries, FD McMaster Laboratory, Locked Bag 1, Armidale, NSW 2350, Australia. C Corresponding author. Email: Robyn.Warner@dpi.vic.gov.au Abstract. The effects of acute exercise stress and electrical stimulation on lamb eating quality and objective measurements of quality were evaluated on the Longissimus thoracis et lumborum (LTL) and the Gluteus medius (GM) muscles. Meat quality attributes were also assessed on the LTL, Semimembranosus (SM) and the Semispinalis capitis (SC) muscles. Forty-eight Poll Dorset × Border Leicester–Merino ewes of about 6 months old were randomly allocated to treatments in a 2 × 2 factorial design, with the respective factors being exercise (Ex, 0 v. 15 min) and post-slaughter low voltage electrical stimulation (control v. ES). In general, exercise reduced the rate of pH fall and increased the ultimate pH of all 3 muscles (P<0.05). This effect was more pronounced in the SM than in the LTL and SC. Exercised LTL and SM muscles also had lower surface lightness (L*) values and higher muscle total water content, indicating an increased incidence of dark cutting meat. Exercised LTL steaks were rated higher for tenderness and juiciness by the taste panelists and had lower Warner-Bratzler shear force values, as is often observed with high ultimate pH meat. Electrical stimulation reduced initial pH (pH 0.5 ) values, but resulted in a slower rate of pH fall in the LTL and SM thereafter. Electrical stimulation resulted in an elevation of temperature at rigor in the SM by 10°C (15 v. 25°C) and in the LTL by 3.1°C (7.4 v. 10.5°C). While no effect of electrical stimulation was observed with instrumental analysis, electrical stimulation reduced sensory tenderness scores and overall liking for the GM, and tended to reduce flavour and juiciness of both the GM and LTL. In conclusion, acute exercise pre- slaughter improved eating quality, but caused dark cutting meat. The negative effect of low voltage stimulation on the eating quality of the GM was probably due to a high rigor temperature and associated heat toughening. Acute exercise stress and electrical stimulation influence the consumer perception of sheep meat eating quality and objective quality traits www.publish.csiro.au/journals/ajea CSIRO PUBLISHING