Assessment of endogenous nitrogen output in adult dogs of contrasting size using a protein-free diet

The purpose of the work was to assess endogenous nitrogen output in dogs of widely contrasting mature body size and genotype. Fecal and urinary nitrogen excretion was measured during 14-day metabolic periods in 25 adult dogs of body-weight range 2.8-51.0 kg fed a protein-free, semipurified diet. Endogenous nitrogen excretion was assumed from day 8 after introduction of the protein-free diet and was measured during the final 7 days of each period. Mean (+/- SEM) endogenous urinary nitrogen (EUN), metabolic fecal nitrogen (MFN), and total endogenous nitrogen (TEN) outputs were 210 +/- 9, 63 +/- 3 and 273 +/- 9 mg/kg 0.75 per day. There were no significant effect of either sex or body weight on the magnitude of EUN, MFN or TEN outputs, however, EUN output was positively and significantly (P less than 0.02) correlated (r = 0.50) with percentage body-weight loss during the metabolic period. The mean values obtained for endogenous nitrogen output in adult dogs agreed closely with previous estimates in the literature for dogs exhibiting a narrower range (8.3-16.7 kg) of mature body weight.