M.F. Miller

Effect of feed energy intake on collagen characteristics and muscle quality of mature cows

Samples from mature cows fed a high-energy and maintenance-energy diet for 84 days prior to slaughter were used to compare collagen solubility and palatability traits. Cows fed a high-energy diet prior to slaughter had increased percentage heat-labile collagen, less sensory panel detectable connective tissue and lower shear force values than cows fed a maintenance-energy diet. Mature cows fed a high-energy diet were fatter and had more marbling than cows fed a maintenance-energy diet. The increased collagen solubility from feeding a high-energy diet to mature cows resulted in palatability and shear force ratings similar to those expected from young animals.

Evaluation of live and carcass techniques for predicting beef carcass composition

Fifty beef animals varying in size, age and composition were used to determine the most accurate methods for determining beef composition. Separable and chemical composition of the 9-10-11th rib section and measurements of subcutaneous fat thickness were the most useful for explaining observed variability in carcass composition. For predicting percentage fat in fed steers, composition of the 9-10-11th rib section was the most accurate [coefficient of determination (R(2) 0·85)]. The 9-10-11th rib section was the most accurate and precise technique identified in this study to estimate beef carcass composition across and within all age classes. Specific gravity accounted for 68% of the variation in percentage of carcass fat across all age classes combined; however, specific gravity did not account for a significant portion of the variation within each age class. Deuterium oxide dilution was able to account for 77% of the variation in chemical fat percentage across all age classes combined; however, deuterium oxide dilution was not as effective in accounting for the observed variation in fat percentage within each age class. Ultrasound was found to be an accurate live measure of chemical fat percentage within all age classes combined.

Bovine Longissimus dorsi muscle glycogen and color response as affected by dietary regimen and post-mortem electrical stimulation in young bulls

Eighty bulls were assigned to one of two groups and fed a dietary regimen to defer or accelerate growth until slaughter. Bulls fed at an accelerated rate of growth (or high energy regimen) had higher post-mortem pH, and lower muscle glycogen stores, with darker lean color, and improved shear and palatability traits compared to deferred fed animals. Bulls fed at an accelerated rate of growth also had a higher degree of marbling and USDA quality grade. Electrical stimulation did not affect (P > 0·05) ultimate pH, but reduced (P < 0·05) glycogen values at 0 and 2 h post mortem. Electrical stimulation also improved muscle color, lowered cooking losses and improved the palatability of cooked longissimus dorsi steaks.

Effect of feeding regimen, breed and sex condition on carcass composition and feed efficiency

Eighty bulls and eighty steers representing four breed types (7/8 Angus. 7/8 Simmental, 7/8 Simmental × 7/8 Angus and 7/8 Simmental × 7/8 Hereford) were randomly assigned to two diets by sex class and breed type. Exotic breeds produced heavier, leaner, more muscular carcasses, with lower USDA quality grades and darker colored, coarser textured lean. Angus 9-10-11th rib composition showed that Angus tended to have less lean, more bone and the most fat when compared to the Simmental and Simmental crosses. Feeding the deferred diet resulted in carcasses with (P < 0·05) less fat, lower USDA quality grade, smaller ribeyes, more sensory panel detectable connective tissue, higher cooking losses and higher Instron shear values. Sex class caused differences (P < 0·05) in feed efficiency, carcass traits and sensory properties.