Effects of slaughter age on meat tenderness and USDA carcass maturity scores of beef females.

Two experiments were conducted to determine the effect of carcass maturity on meat palatability using concentrate-fed cattle of known history and to determine the relationship of chronological age to carcass maturity scores. Yearling heifers (n = 28) and 2-yr-old cows (n = 25) of similar breed groups were fed a high-energy-density diet for 90 d before slaughter. Longissimus muscle Instron peak load (Warner-Bratzler shear force) did not differ between age groups; but, fail elongation was higher for the 2-yr-old cows (P < .05). Overall tenderness ratings were lower for the 2-yr-old cows; however, the magnitude of the tenderness difference between age groups was small (.4 units on an 8-point scale). There was 10-fold more variation in tenderness within each age group than there was between age groups. Carcass maturity scores and chronological age were compared for heifers and cows (n = 249) ranging in age from 1.7 to 13.9 yr. Carcass maturity scores increased with increasing chronological age at a much faster rate than indicated by USDA. The following chronological age groups most accurately reflected the chronological age associated with each USDA carcass maturity class: A, 9 to 24 mo; B, 24 to 36 mo; C, 36 to 48 mo; D, 48 to 60 mo; E, > 60 mo. These results indicate that efforts to control variation in tenderness would be more effective if they targeted factors that have a greater effect on meat tenderness than does maturity class. Moreover, our results indicate that cows may grade lower at a given age than what USDA standards imply.