Low ultimate-pH of beef is desirable because it increases shelf life and has beneficial effects on colour and tenderness. Industry recommendations are that beef animals are not exercised strenuously prior to trucking, as this may trigger depletion of muscle glycogen and lead to higher beef pH. In 2 experiments, 400-500 kg 18-month-old steers were exercised at a range of intensities up to 5 km distance at 8 km/hr. Biopsy samples from the longissimus dorsi muscle were taken and glycogen concentration measured. Although plasma lactate levels were elevated by exercise there was no significant depletion in muscle glycogen concentration (average 17.7 mg/g tissue). Depletion may have occurred had animals been heavier and fatter, or if the exercise regime had been more severe. Alternatively, it may be that at the level of exercise imposed (which was severe by farm-practice standards), animals also needed to be emotionally stressed in order to precipitate a depletion of glycogen, through a combination of muscle contractile and adrenergic reactions.
Proceedings of the New Zealand Society of Animal Production, Volume 58, , 243-244, 1998
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