Results are presented from a study of 42 steers relating whole-body and carcass K40 contents, as measured by a large-volume, liquid scintillation counter, to carcass lean muscle mass as measured by chemical analysis. Variations in the amount of radioactivity of the gastrointestinal contents, in the counting efficiency of the whole-body counter and in the positioning of the steers with respect to the scintillation detector were found to be the main sources of error affecting the precision of estimated whole-body potassium and the precision with which the carcass lean muscle mass could be predicted. With procedures developed to account for, or minimize the above sources of variation, wholebody count was repeatable from day to day to within 2 or 3% in 21 steers and predicted carcass lean with standard errors of estimate less than 3% within two narrow weight ranges. Carcass K40 measurements predicted carcass lean with standard errors of estimate somewhat greater than the whole-body count (3.5%). Body potassium can be measured precisely enough to suggest practical utility of the K40 method for determining carcass lean muscle mass in live steers and in steer carcasses.
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Lohman et al. (1966) studied this question.