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

There is evidence that, in cattle, rapid compensatory growth after a period of growth restriction may increase the variability of beef quality and tha t variability is greater in breeds which reach larger body site at maturity . This experiment investigated the effect of compensatory growth following a period of winter grow,th restriction on carcass quality in steers of smal l and large mature size grazed on pasture. Angus (no. = 120) and South Devo n x Angus (SDxA; no. = 120) steers were allocated to non-restricted or rest ricted growth treatment groups and for 126 days over winter their grazing w as managed to achieve mean live-weight gains of approximately 0.7 kg/day or to maintain live weight for each group respectively. Steers were slaughter ed 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. Thereaft er remaining steers were grazed together at a high pasture allowance to max imize growth and were slaughtered for carcass evaluation as they reached ta rget live weights (Angus, 590 kg; SDxA, 620 kg). SDxA steers grew faster (P < 0.05) during both the winter and finishing periods and reached target sl aughter live weights approximately 20 days earlier than Angus steers. SDxA steers also had leaner carcasses than Angus steers at each slaughter althou gh there was no significant difference in meat quality between breeds. Howe ver there was a significant effect of restriction treatment on carcass weig ht and meat quality. The non-restricted steers grew faster, had heavier car casses 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 ga in during the finishing period suggesting increased potential for post-mort em myofibrillar proteolysis and therefore increased meat tenderness. Howeve r, in the present experiment this teas confounded by an increase in shear f orce with age-at-slaughter, especially in the non-restricted steers. Nevert heless, steers which were heaviest at the start of the experiment reached s laughter live weight earliest, were leaner than average and had higher calp ain system activities at slaughter regardless of breed or restriction treat ment. Furthermore, in the non-restricted group, high initial live weight an d early slaughter was associated with lower pH and more tender meat. In con clusion, although restriction affected meat quality attributes, it appears that live weight prior to food restriction also had a considerable effect o n carcass characteristics at slaughter Therefore, the characteristics of th e early growth phase prior to the finishing period may have important conse quences for meat quality.