Body Composition of Live Animals as Determined by K40. I. A Crystal-Type, Whole-Body Counter for Determining Body Composition of Live Animals

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Abstract
The Colorado State University whole-body counter was designed to measure body burdens of Csl37 and total body K in large animals by gamma-ray spectrometry. The shield is a 2.44 m cube of 20.3-cm-thick steel walls and weighs 68 metric tons. The detector is a single 23- by 10-cm Nal (Tl) scintillation crystal. Lean-body mass (LBM) was studied in Holstein cattle by measurement of K40 and, hence, total body K. The concentration of K in LBM was determined by slaughter and rendering experiments. Potassium was determined in the carcass components by large sample gamma-ray spectrometry and fat by pentane extraction. The calibration figures for a 450 kg Holstein was 4.0 counts/30 min./g of body K. Animals are carefully washed before counting and counted in a modified squeeze chute for 30 min. with the crystal over the rump of the animal. A series of 12 weekly counts on a Holstein cow indicated a coefficient of variation of 2.82% on the estimate of total body K. During the spring fo 1965 there was opportunity to observe the effects of short-lived fallout fission products from ingesta present in the rumen. Only Ba-Lal40, due to its high energy gamma-ray, significantly interfered with the estimate of either Csl37 or K40.

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