A Comparison of Two Noninvasive Techniques to Measure Total Body Lipid in Live Birds

Abstract

ABSTRAcr.-Total body electrical conductivity (TOBEC) and near infrared interactance (IRI) are noninvasive techniques with potential utility for monitoring body composition of freeranging birds or captive experimental subjects. I used live Northern Bobwhites (Colinus virginianus) to validate these methods for estimation of total body lipid. Total body electrical conductivity and IRI measurements were compared with body composition as determined by solvent extraction of carcasses. I measured IRI at three body sites (subscapular, pectoralis, and subfemoral) on 42 bobwhites. Only the subscapular and pectoralis sites yielded IRI measurements that were significantly correlated with percent body lipid, but IRI from these sites explained only 17.5% and 10.0% of the variation in percent body lipid, respectively. The cause of the low correlations is unknown, but it was not a function of differences in subject posture or light-wand position between replicate measures on the same subject. Total body electrical conductivity measurements explained 92% of the variation in lean body mass in a sample of 62 bobwhites. Measurements were affected by small differences in subject movement and position in the measurement chamber. There was no significant difference in TOBEC of subjects with or without aluminum leg bands. Measurements obtained from the same subjects with two different SA-1 TOBEC analyzers were not significantly different. The residuals about the regression of TOBEC against lean body mass were not correlated significantly with body temperature, but were significantly correlated with hydration. Total body electrical conductivity explained 99.1% of the variation in lean body mass when only those data from normally hydrated and properly restrained subjects were included (n = 38). Estimated body lipid from TOBEC measurements was highly correlated with total body lipid (R = 0.96) as determined by solvent extraction. The 95% confidence limits from the inverse regression procedure for the estimate of total body lipid from TOBEC measurements were ?4.75 g at 25 g lipid, ?4.85 g at 10 g lipid, and ?5.62 g at 50 g lipid. Estimated total body lipid from TOBEC measurements was on average within 10% of total body lipid from solvent extraction. Although IRI analysis failed to yield a suitable index to body composition, TOBEC analysis provided an accurate estimate of total body lipid in live bobwhites. Received 30 July 1990, accepted 4 December 1990.