ABSTRACT
One hundred forty-four Angus male calves were assigned to one of five slaughter-age groups: 9, 12, 15, 18 and 24 mo of age. After weaning, one-half of the calves within slaughter age were castrated. One-half of the 12-, 15-, 18- and 24-mo age groups of each sex were further randomly allotted to a high-energy (HE) or low-energy (LE) finishing diet. Eight bulls and eight steers assigned to the 9-mo slaughter group were fed the HE diet only. Samples from the longissimus muscle (LM) were taken at the 12th rib for histological evaluations of fat deposits. Thin sections from the LM at the 11th rib were stained for lipid, collagen and elastin. Steaks from the LM were cooked and evaluated by a sensory panel and sheared by a Warner-Bratzler shear (WBS) device. The 9-10-11th rib sections were separated into muscle, fat and bone. Collagen, elastin and collagen solubility were determined chemically. Bulls had heavier carcasses, less fat and lower sensory scores for tenderness and juiciness than steers. Steers fed the HE diet had lower WBS values than bulls on either diet. Cooking losses were higher for bulls at 12, 18 and 24 mo than for steers. Histological evaluation showed that collagen content was higher for bulls than for steers and higher for cattle fed the LE diet than those fed the HE diet. Among cattle on the HE diet, the 9-mo cattle had more collagen than all older groups. Neither sex nor diet had an effect on elastin content shown by histological evaluation, but 12-mo cattle had the most elastin and the 15- and 18-mo cattle had the least elastin. Collagen content determined by chemical analysis was not affected by sex, diet or slaughter age. Correlation coefficients among histologically and chemically evaluated collagen and elastin and meat traits were too low to be of practical importance. The time-intensive histological techniques used in our study provided little additional information over that obtained from visually evaluated or chemically measured meat traits.
