An Evaluation of Whole Body Potassium-40 Content for Estimating Lean and Fat Mass in Pigeons’

A severe limitation in studies of avian ecological energetics is the lack of an accurate, noninvasive technique for determining whole body fat storage in living birds. We explored a technique of assaying total body potassium as a predictor of lean mass (LM) and then derived fat mass (FM) by subtracting LM from total body mass. Body potassium ’ Received 15 December 1997. Accepted 3 April 1998. (K), present in lean tissue but not in fat, was estimated noninvasively from naturally-occurring radioactive 40K, which occurs as a fixed ratio to total body K. We assayed 29 pigeon (Columba livia) carcasses for 40K and then measured LM from body composition analyses in which fat mass was extracted using petroleum ether. The @K results were regressed against LM using five different combinations of independent variables. Regression equations were tested by comparing predicted LM (and FM predictions by subtraction from body mass) to measured LM values obtained from a 580 SHORT COMMUNICATIONS separate group of pigeons. Whole body assay of 4oK within a 250 kiloelectron volt (keV) region of interest was not a useful predictor of LM in pigeons (9 = 0.5 1; surrounding the 1.46 megaelectron volt (MeV) total mean absolute error was 14 2 7%). Absolute errors absorption peak of 40K. Contributions from backincreased with FM predictions (96 i 50%). Adding ground counts were regularly determined and subtractbody mass as an independent variable increased the 9 ed from the gross counts. to 0.97, but body mass alone explained 96% of the Efficiency in detecting 40K partially depends upon variability in LM. the size and number of NaI crvstals used for the anal