Muscle, Fat and Bone in Serially Slaughtered Large Dairy or Small Beef Cattle Fed Corn or Corn Silage Diets in One of Two Locations

The 9th–10th–llth rib sections from one side of each of 37 small-framed Angus and 34 Holstein steers slaughtered at five weights within breed were dissected into muscle, fat and bone. One-half of the steers of each breed were fed ad libituma high corn grain diet; the other half were fed ad libituman all-corn silage diet. One-half of the animals in each breed-diet group were housed conventionally, and half were housed in a warmer environment with movement restricted to individual pens. When rib weight was used as a covariate, analyses showed that Holstein steers had more (P<.005) muscle, less (P<.005) fat and more (P<.005) bone than Angus steers. At the same rib weight, grain-fed cattle had .12 kg more (P<.05) fat and .04 kg less (P<.05) bone than silage-fed cattle. Muscle content was not significantly affected by diet. While location did not affect tissue deposition in Holstein steers, Angus housed in the individual pens deposited more (P<.05) fat and less (P<.05) muscle in a given weight of rib than Angus steers housed conventionally. At the same ribeye area, Holsteins had more (P<.005) dissectable muscle than Angus, indicating that the longissimusmuscle is longer with a smaller diameter in Holstein than in Angus steers. Although at a given weight of rib, muscle to bone ratios were higher (P<.005) for Angus than for Holstein steers, analyses of covariance using bone as a covariate and a plot of muscle against bone showed that Angus and Holstein muscle data were part of the same (P>.10) population. Thus, differences in cattle shape were not reflected by different amounts of muscle at the same weight of bone. Use of muscle to bone ratio would have led to the incorrect conclusion that Angus have more muscle at the same weight of bone. Therefore, regression of muscle on bone is both biologically and statistically more satisfactory for interpretation of muscle growth and development patterns in cattle.