Effects of growth pathway on beef quality in 18-month-old Angus and South Devon ✕ Angus pasture-fed steers

Abstract

AbstractThere is evidence that, in cattle, rapid compensatory growth after a period of growth restriction may increase the variability of beef quality and that variability is greater in breeds which reach larger body size at maturity. This experiment investigated the effect of compensatory growth following a period of winter growth restriction on carcass quality in steers of small and large mature size grazed on pasture. Angus (no. = 120) and South Devon ✕ Angus (SD✕ A; no. = 110) steers were allocated to non-restricted or restricted growth treatment groups and for 126 days over winter their grazing was managed to achieve mean live-weight gains of approximately 0·7 kg/day or to maintain live weight for each group respectively. Steers were slaughtered at the start (no. = 10 per breed) and end (no. = 20 per nutrition group (10 from each breed)) of the winter period for carcass evaluation. Thereafter, remaining steers were grazed together at a high pasture allowance to maximize growth and were slaughtered for carcass evaluation as they reached target live weights (Angus, 590 kg; SD✕ A, 620 kg). SD✕ A steers grew faster (P< 0·05) during both the winter and finishing periods and reached target slaughter live weights approximately 20 days earlier than Angus steers. SD✕ A steers also had leaner carcasses than Angus steers at each slaughter although there was no significant difference in meat quality between breeds. However, there was a significant effect of restriction treatment on carcass weight and meat quality. The non-restricted steers grew faster, had heavier carcasses and more tender steaks than restricted steers, although there was no significant difference in carcass fatness (adjusted for hot carcass weight). Muscle calpain activities were positively correlated with live-weight gain during the finishing period suggesting increased potential for post-mortem myofibrillar proteolysis and therefore increased meat tenderness. However, in the present experiment this was confounded by an increase in shear force with age-at-slaughter, especially in the non-restricted steers. Nevertheless, steers which were heaviest at the start of the experiment reached slaughter live weight earliest, were leaner than average and had higher calpain system activities at slaughter regardless of breed or restriction treatment. Furthermore, in the non-restricted group, high initial live weight and early slaughter was associated with lower pH and more tender meat. In conclusion, although restriction affected meat quality attributes, it appears that live weight prior to food restriction also had a considerable effect on carcass characteristics at slaughter. Therefore, the characteristics of the early growth phase prior to the finishing period may have important consequences for meat quality.