Growth, carcass, and tenderness characteristics of virgin, spayed, and single-calf heifers

Fifty-three Angus/Gelbvieh rotationally crossed heifers were slaughtered after 100 d on a high-concentrate diet. The average slaughter age for each of three different groups was 31, 33, or 35 mo, which falls within the USDA's 30- to 42-mo age range for animals producing "B" maturity carcasses. Each age group consisted of five or six heifers that had never been bred (virgin), six heifers ovariectomized at 1 yr of age (spayed), and six heifers that had weaned calves approximately 120 d postpartum (single-calf). Slaughter weight was higher (P < .05) for the virgin heifers but total weight gain in the feedlot was similar among the three groups. Single-calf heifers fed 100 d after weaning calves 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 indicated single-calf heifers matured earlier (P < .05) than the other groups. Panel tenderness and Warner-Bratzler (WB) shear values of rib roasts from virgin, spayed, and single-calf heifers were determined. No differences among groups of heifers existed but scores within each group varied greatly. Marbling score was correlated (P < .05) with panel tenderness and shear force and the hydroxylysylpyridinium (HP) crosslink of muscle collagen was correlated (P < .05) with shear values. Because no significant (P < .05) correlation existed between HP in bone collagen or HP or WB shear values in muscle, we concluded that collagen maturation processes in muscle and bone occur independently. With the exception of differences in bone maturity scores, few meaningful differences in characteristics of virgin, spayed, and single-calf heifers existed, but these maturity differences could change carcass grade and influence value.