ESTIMATION OF NITROGEN-CORRECTED METABOLIZABLE ENERGY VALUE OF LABORATORY CANINE DIETS

This study evaluates the reliability of the equation, metabolizable en ergy (ME) = digestible energy (DE)-1.25 x digestible crude protein (DC P), as a means of estimating the energy value of non-purified diets fo r laboratory dogs. To do this, five digestion and nitrogen-balance (NB ) trials and determination of the energy value of a diet were conducte d using five diets and four mature, male Beagles for each experiment. The resulting digestibility of crude protein, acid ether extract, and nitrogen-free extract of these diets were 79.5%, 91.6%, and 84.8%, res pectively. The NB in every diet was positive : 1.4-8.6mg/g dry matter of ingested diet. Of the nitrogen (N) ingested, 21% was excreted into feces, 66% was excreted into urine, and 13% was retained. In terms of dietary gross energy (GE), 18% was lost in feces and 5% was excreted i nto urine leaving 77% as ME. Retained energy in the body was only 1%, and N-corrected metabolizable energy (MEn) was 76% of GE. The average urinary energy (UE) loss per gram of urinary N was 7.84kcal. The corre lation between UE/DCP and NB values is statistically significant : UE/ DCP = 1.24-0.03NB, r = 0.798, P < 0.001. Therefore, UE/DCP is 1.24kcal /g at N-equilibrium, almost the same as the factor in the above equati on. The ME value calculated by the equation is identical to the MEn va lue, and both are significantly lower (P < 0.05) than the empirically determined ME value. We conclude that this equation should be expresse d as MEn = DE-1.25DCP, and is a reliable and convenient means of estim ating the MEn of diets. Also, this study demonstrates that this revise d equation can be applied, in the case of dogs, not only at N-equilibr ium but also when N is retained in the body.