Colour of muscle from 18-month-old steers given long-term daily exercise

Abstract

Darker beef from pasture-fed compared with grain-fed cattle may result from differences in physical activity rather than differences in nutrition. The objective was to determine if steers that were exercised produced darker meat than non-exercised steers and whether any effect was muscle-related. Exercised steers were walked 4.41 km daily in a single bout, six days per week for 18 weeks at an average speed of 5.2 km h −1. All steers were fed grass silage on an ad libitum basis plus 6 kg concentrates. Following slaughter, muscle colour coordinates (‘ L’ (lightness), ‘ a’ (redness) and ‘ b’ (yellowness) values) of M. longissimus dorsi (LD), M. semimembranosus (SM) and M. extensor carpi radialis (ECR) were recorded at 48 h postmortem and redness and yellowness were used to calculate muscle hue (‘ H’) and colour intensity/saturation (‘ C’). The pH of all muscles was measured at 1.5, 3, 6, 22 and 48 h postmortem and LD samples were recovered (90 min postmortem) for glycolytic potential (GP) assessment. Exercise did not affect muscle lightness, yellowness, hue or colour intensity. However, LD was the darkest ( P < 0.001) and SM the most saturated ( P < 0.001) muscle. Exercise affected muscle redness in a muscle-dependent manner (muscle × exercise, P = 0.038) whereby ECR became more red with exercise but LD and SM were unaffected. There were muscle × time ( P < 0.001) and time × exercise ( P = 0.045) interactions for muscle pH. The ECR muscle had the highest pH at all times. The exercised steers had higher ( P < 0.05) LD muscle pH than control steers at 3 and 6 h postmortem. Exercise did not affect myoglobin concentration, which was muscle dependent, decreasing in the order: SM (6.72 mg/g) > ECR (6.33 mg/g) > LD (5.48 mg/g), which were all different ( P < 0.001). Exercise had no effect on GP in LD muscle (111 vs. 99 μmol/g for control and exercised steers, respectively; SED = 6.6 μmol/g). It was concluded that although application of exercise did not affect muscle lightness and thus, did not cause ‘darker’ meat, it did affect muscle redness in a muscle-dependent manner.