Abstract
This study evaluates the reliability of the equation, metabolizable energy (ME) = digestible energy (DE) -1.25×digestible crude protein (DCP), as a means of estimating the energy value of non-purified diets for laboratory dogs. To do this, five digestion and nitrogen-balance (NB) trials and determination of the energy value of a diet were conducted 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%, respectively. 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 into 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 correlation 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 equation. The ME value calculated by the equation is identical to the MEn value, and both are significantly lower (P<0.05) than the empirically determined ME value. We conclude that this equation should be expressed as MEn=DE-1.25DCP, and is a reliable and convenient means of estimating the MEn of diets. Also, this study demonstrates that this revised equation can be applied, in the case of dogs, not only at N-equilibrium but also when N is retained in the body.
