DENSITOMETRY-BASED EQUATIONS FOR ESTIMATING BODY-COMPOSITION IN FISCHER RATS

Male Fischer rats are widely used to evaluate the effects of nutrition al repletion or deprivation on the rat's nutritional status. Practical methods are needed to evaluate changes in body composition. Chemical analysis is expensive, time consuming, and often not available; bioele ctrical impedance analysis in laboratory animals lacks standardization . Postulating that the measurement of densitometry would allow reliabl e estimation of body composition in the male Fischer rat, we studied 2 7 male Fischer rats. Densitometric measurements of the carcasses and t heir chemical analysis were performed to obtain reference values. Init ial estimation of the fraction of body fat based on densitometry was a ttempted with the Siri equation intended for use in humans. We found t hat this equation was not suitable for use in the male Fischer rat bec ause it underestimated fat mass at high carcass weights and overestima ted fat mass at low carcass weights. Therefore, the Siri equation was modified to more accurately predict carcass composition in the male Fi scher rat. Three different predictive equations based on simple densit ometric measurements were developed that allow separate estimation of carcass fat, carcass water, and carcass protein in the male Fischer ra t. These equations were found to be accurate to within 2-5-3% of carca ss weight.