Evaluation of 40K Count as a Predictor of Muscle in Yearling Beef Bulls

Carcass merit is an important characteristic of a beef animal, however, its incorporation into a selection program requires some means of effective measurement on the live animal. Current procedures for determining the breeding value of prospective herd sires with respect to carcass traits by slaughtering a random sample of their progeny and/or sibs are costly and time consuming. Anderson (1959) proposed the use of wholebody counters to estimate the quantity of muscle in an animal by counting the emission of gamma rays from the radioactive isotope 40K. Natural potassium has been shown to contain a constant proportion of 40K (Vinogradov, 1957), however, the constancy of muscle potassium as a proportion of total body potassium is still a subject of discussion. Lohman and Norton (1968) found 53.4% of the total potassium in steers was located in the separable lean and observed variation in potassium content of muscle among breed groups but not among weight groups.