GROWTH, CARCASS, AND TENDERNESS CHARACTERISTICS OF VIRGIN, SPAYED, AND SINGLE-CALF HEIFERS

Fifty-three Angus/Gelbvieh rotationally crossed heifers were slaughter ed after 100 d on a high-concentrate diet. The average slaughter age f or each of three different groups was 31, 33, or 35 mo, which falls wi thin the USDA's 30- to 42-mo age range for animals producing ''B'' mat urity carcasses. Each age group consisted of five or six heifers that had never been bred (virgin), six heifers ovariectomized at 1 yr of ag e (spayed), and six heifers that had weaned calves approximately 120 d postpartum (single-calf). Slaughter weight was higher (P < .05) for t he virgin heifers but total weight gain in the feedlot was similar amo ng the three groups. Single-calf heifers fed 100 d after weaning calve s tended to be fatter than virgin or spayed heifers. Carcass maturity scores for the single-calf, virgin, and spayed heifers were different (P < .05); single-calf heifers produced carcasses that appeared older and spayed heifers produced carcasses that appeared younger. Maturity scores coupled with lighter and shorter metacarpal bone weights indica ted single-calf heifers matured earlier (P < .05) than the other group s. Panel tenderness and Warner-Bratzler (WB) shear values of rib roast s from virgin, spayed, and single-calf heifers were determined. No dif ferences among groups of heifers existed but scores within each group varied greatly. Marbling score was correlated (P < .05) with panel ten derness and shear force and the hydroxylysylpyridinium (HP) crosslink of muscle collagen was correlated ( P < .05) with shear values. Becaus e no significant (P < .05) correlation existed between HP in bone coll agen or HP or WB shear values in muscle, we concluded that collagen ma turation processes in muscle and bone occur independently. With the ex ception of differences in bone maturity scores, few meaningful differe nces in characteristics of virgin, spayed, and single-calf heifers exi sted, but these maturity differences could change carcass grade and in fluence value.