In this study, 20 young steers received no beta-agonist (C) and 100 animals all received zilpaterol hydrochloride (Z), with 1 group receiving Z while the other 4 groups receiving Z and vitamin D 3 at the following levels (IU/animal/day) and durations before slaughter: 7 million for 3 days (3D7M) or 6 days (6D7M), 7 million for 6 days with 7 days no supplementation (6D7M7N) and 1 million for 9 days (9D1M). Left carcass sides were electrically stimulated (ES) and right sides not (NES). Samples were analysed fresh or vacuum-aged for 14 days post mortem. Parameters included drip loss and instrumental colour measurements. In general, zilpaterol showed increased drip loss, lighter meat, and reduced redness. Vitamin D 3 supplementation could not consistently overcome these negative effects. All vitamin D 3 treatments reduced drip loss of stimulated aged steaks.Keywords: Vitamin D 3 , zilpaterol, electrical stimulation, calpains, meat tenderness # Corresponding author. E-Mail: pstrydom@arc.agric.za 2
IntroductionPhysical appearance of retail meat cuts during display is a critical link in the first step of the consumer satisfaction process. The bright red colour of red meat is the most important quality attribute to a consumer at the point of purchase (Jeremiah et al., 1972, Killinger et al., 2004and Kropf, 1980. In addition, unacceptable water holding capacity, resulting in increased driploss in packaging that is unattractive to consumers, more susceptible to bacterial growth and that leads deterioration of eating quality (Lagerstedt et al., 2011 and Vázquez et al., 2004). Various pre-harvest, harvest and post-harvest processes could affect the colour and water holding qualities of meat.Beta-agonists are supplemented to feedlot cattle to improve weight gain and feed efficiency and increase carcass yield (Dikeman, 2007, Dunshea et al., 2005, Kellermeier et al., 2009). However, beta-agonists also induce muscle toughness in supplemented animals Holmer et al., 2009) especially in ruminants, mainly due to an increase in activity of the inhibitor calpastatin and a reduction in calpain activity ( Koohmaraie and Shakelford, 1991, Strydom et al., 2009 and Wheeler and Koohmaraie, 1997. In addition, various studies have reported effects on other quality attributes like colour and water holding capacity (Avendaño-Reyes et al., 2006, Geesink et al., 1993, Gonzalez et al., 2009, Rogers et al., 2010 and Vestergaard, Sejrsen and Klastrup, 1994, which could probably be associated with the shift in fibre type composition (more glycolytic or white) ( Geesink et al., 1993, Gonzalez et al., 2009, Strydom et al., 2009 and Vestergaard, Henckel, Oksbjerg and Sejrsen, 1994 and muscle hypertrophy (Kellermeier et al., 2009) caused by beta-agonists. It is also well-known that processes like electricalstimulation and post mortem ageing may affect colour (Devine et al., 2002, Ledward, 1985, Ledward et al., 1968 and Renerre, 1990) and water holding capacity (Den Hertog-3 Meischke et al. , Devine, 2009 and Strydom et al., 2005 and that t...