2.1. Animals and muscle samples
A total of 161 Large White pigs (81 gilts and 80 castrated pigs) with an average initial body weight of 34.5±6.7 kg (initial age 86.0±4.2 days), heterozygous for the halothane gene and clinically healthy, were used in this study. All pigs were tested to assure the halothane genotype according to Fujii et al. (1991). All pigs were weighed at the beginning and end of the experiment, and the average daily gain was calculated in this period. All treatments and experimental procedures were approved by the Ministry of Food, Agriculture, Forestry, and Fisheries in Korea. Pigs were reared on a commercial farm in separate pens (10–11 pigs per pen with 0.8 m2 space per pig), and fed the same commercial diet in accordance with the National Research Council (1998). All pigs were transported to a commercial abattoir under the same handling conditions at a similar age (175.5±4.1 days old; 102.9±11.3 kg) in 4 batches (40, 40, 40, and 41 pigs per batch) during the winter period, using standard procedures under the supervision of the Korean grading service for animal products.