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Effects of Feeder-Cattle Frame Size and Muscle Thickness on Subsequent Growth and Carcass Development. II. Absolute Growth and Associated Changes in Carcass Composition^1,2,

Colorado State University⁶, Fort Collins 80523

Abstract

Data from a serial slaughter of 324 steers were used to determine the effects of feeder-cattle frame size (Large, L: Medium, M; Smal), S) and muscle thickness (No. 1, No. 2, No. 3) on absolute growth and carcass development. Yearling feeder steers representing nine frame-size x muscle-thickness subclasses were backgrounded 28 d; subsamples of steers (n = 6) from each subclass were slaughtered at 28-d intervals (O, 28, 56, 84, 112 or 140 d) during a 140-d finishing period. One side from each carcass was dissected into muscle, bone and fat. Absolute growth during finishing was linear. AUometric growth coefficients for muscle, bone and fat were similar for all nine subclasses. Frame size was related (P<.01) to differences in absolute growth rate (L>S), compositional maturity at a common carcass weight (S>M>L) and slaughter weight at a constant carcass-fat percentage (L>M>S). Muscle thickness did not influence absolute growth rate, but was associated with differences (P<.01) in carcass muscle-to-bone ratio at a common bone weight and in muscle percentage when carcass fatness was statistically standardized. The effects of muscle thickness on carcass composition were most pronounced within the large-framed group. Relationships of these results to the USDA feeder-cattle grading principles are discussed.

¹ Sci. Ser. Paper No. 2989 published with the approval of the Colorado State Univ. Agr. Exp. Sta. This research was supported by the USDA Agr. Marketing Serv., and the Colorado Dept. of Agr. under the Federal-State Marketing Improvement Program.

² The authors express appreciadon to Mr. W. E. (Ned) Tyler for his contirbutions in design and direction of the experiment and to R. P. Clayton, D. A. Daley, B. K. Klein, W. R. Uoyd, R. K. Miller, C. W. Moran, M. D. Self, T. D. Stromberg, M. L. Wittler and D. W. Woodburn for their assistance in data collection.

³ Present address: Dept. of Anim. Sci., Oklahoma State Univ., Stillwater, OK 74078.

⁴ Livestock Division, Agr. Marketing Serv., USDA.

⁵ Monfort of Colorado, Inc. Greeley, CO.

⁶ Dept. of Anim. Sci.