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Gut Endogenous Nitrogen and Amino Acid Excretions in Adult Domestic Cats Fed a Protein-free Diet or an Enzymatically Hydrolyzed Casein-Based Diet¹

Monogastric Research Centre, Department of Animal Science ^* Department of Physiology and Anatomy, Massey University, Palmerston North, New Zealand

Ileal and fecal gut endogenous nitrogen and amino acid excretions in adult domestic cats were determined. Ileal digesta were collected (10 cm of terminal ileum) from the cats fed either a protein-free diet or an enzymatically hydrolyzed casein-based diet (free amino acids and peptides < 10,000 Da) for 1 wk. Chromic oxide was included in each diet as an indigestible marker. The relative contribution of the hindgut to total endogenous gut excretion was investigated in a separate study by feeding cats a protein-free diet with or without added antibiotics for 10 d. Endogenous ileal nitrogen and amino acid nitrogen excretions of (mean ± SEM) 2.4 ± 0.27 and 1.9 ± 0.13 mg/g food dry matter intake, respectively, were found for the cats fed the protein-free diet, whereas higher excretions of 3.6 ± 0.73 (P = 0.12) and 3.6 ± 0.76 (P = 0.03) mg/g food dry matter intake were obtained in cats fed the enzymatically hydrolyzed casein. Significantly (P < 0.05) higher endogenous ileal amino acid excretions, for the enzymatically hydrolyzed casein-fed cats compared with those fed the protein-free diet, were found for methionine, aspartic acid, serine, glutamic acid, proline, valine and isoleucine, with the differences in excretions of glycine, alanine, leucine and histidine being significant at the 6% level. Most of the endogenous fecal amino acid excretions were unaffected by the inclusion of the antibiotics in the protein-free diet, although bacterial numbers were significantly lower (69%). Antibiotics addition led to significantly higher fecal endogenous excretions of nitrogen, taurine, threonine, serine and histidine but significantly lower excretions of methionine and lysine. Cats, like other simple-stomached mammals, excrete higher amounts of endogenous amino acids at the terminal ileum when the diet contains peptides.

KEY WORDS: • cats • endogenous loss • amino acid • ileal • fecal

¹ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

² To whom correspondence should be addressed: Monogastric Researdh Centre, Department of Animal Science, Massey University, Private Bag 11222, Palmerston North, New Zealand.

Manuscript received 31 July 1995. Revision accepted 4 January 1996.