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Utilization of Breed and Traits Determined from the Live Beef Steer for Prediction of Marbling Score¹

Washington State University, Pullman

Abstract

Carcass data were collected from 415 Angus, 852 Hereford, 160 Shorthorn and 283 Crossbred steers. The results of this study indicate that Angus carcasses had the largest longissimus areas per 45.4 kg carcass, the highest conformation and marbling scores and the highest U.S.D.A. quality grades (all P<.01) among the breed groups compared. Carcasses from Hereford steers exhibited the lowest percents of internal fat, and the lowest marbling scores and U.S.D.A. quality grades (all P<.01). Shorthorn carcasses possessed the smallest longissimus areas, the highest percents of kidney, pelvic and heart fat, the lowest conformation scores and the lowest values for cutability index (all P<.01). Crossbred carcasses were intermediate in most of the carcass traits, although they exhibited nonsignificant advantages in weight, longissimus area and fat thickness measurements. Levels of fat thickness and live weight were noted in each breed group beyond which increases in weight or fatness were not associated with concomitant increases in marbling score. These levels approximate 4.0 mm of fat thickness per 45.4 kg carcass and 499 kg live weight for all breed groups except Herefords which reach this level at a higher live weight.

Results of the present study document differences between breeds in marbling score and suggest little accuracy in estimating exact marbling score on a within-breed basis. Carcasses from Angus steers met or exceeded the minimum amount of marbling necessary to grade U.S. Choice at the lowest weight and fat thickness levels included in this study. Under the assumptions made herein, one can be 95% confident that the true mean marbling score will be sufficiently high to produce carcasses grading Choice if slaughter steers are: Angus weighing 340 kg and/or possessing 2.5 mm of subcutaneous fat cover; Herefords weighing 453 kg and/or exhibiting 12.7 mm of fat cover over the longissimus; and Crossbred or Shorthorn steers weighing 415 kg and/or possessing 12.7 mm of fat thickness at the 12th rib.

¹ Scientific Paper No. 3350, Washington Agricultural Research Center.

² Present Address: Department of Animal Science, Texas A & M University.

³ Department of Animal Sciences.

⁴ The authors acknowledge the assistance of the following County Extension Agents in the collection and summarization of data: John W. Bernard, Phillip E. Bloom, Lawrence L. Brown, Richard W. Brown, Joe S. Maxwell, Edgar C. Reif and W. Douglas Warnock.