Current perspectives on the darker beef often reported from extensively-managed cattle: Does physical activity play a significant role?

Although frequently confounded by many factors, cattle raised outdoors on pasture are consistently reported to have darker muscle than cattle raised indoors. Exercise may play a key role. Colour differences apparently caused by nutrition are often confounded by environmental factors which may provide cattle with increased opportunities or requirements for activity. Furthermore, when slaughtered at similar ages and levels of fatness, diet composition (as opposed to energy level) does not appear to effect statistically significant variation in all muscle colour attributes in adult bovines or is at best inconsistent. The increased opportunity for pastured cattle to engage in activity, including grazing, rather than their grass diet per se may contribute to physiological and metabolic adaptation in muscle sufficient to alter qualitative and quantitative biochemical aspects of muscle metabolism, manifested as differences in post-mortem muscle colour. Concomitant changes in associated muscle fibre types and biochemical pathways usually occur, notably a shift towards oxidative metabolism. However, effects may depend on the age of the animal and duration, amount and intensity of activity and may be muscle-specific. Any effects of exercise on muscle characteristics, including colour, are likely to involve complex adaptive and interactive responses perhaps under all or some combination of genetic, nutritional and endocrinological control so that effects of dietary composition and energy, growth rate and growth path, amongst others, reflected in carcass and meat quality differences between extensively- and intensively-managed bovines, cannot be conveniently overlooked.