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Nutrient Metabolism

Net Protein Oxidation Is Adapted to Dietary Protein Intake in Domestic Cats (Felis silvestris catus)¹

Kim Russell^*2, Peter R. Murgatroyd and Roger M. Batt^*

^* Waltham Centre for Pet Nutrition, Waltham on the Wolds, Melton Mowbray, Leics LE14 4RT, UK and the Department of Clinical Biochemistry, University of Cambridge, Addenbrookes Hospital, Cambridge2 2QR, UK

²To whom correspondence should be addressed. E-mail: kim.russell{at}eu.effem.com

Cats have a requirement for dietary protein two to three times that of omnivores and herbivores. This was reported to be due to the hepatic catabolic enzymes of this species being set to a permanently high level and, therefore, showing little adaptation to low dietary protein. A major mechanism for adapting to dietary protein in other species is amino acid oxidation (hereafter referred to as protein oxidation), and the objective of this study was to determine whether protein oxidation in cats was correlated with protein intake. Net protein and net fat oxidation in six adult cats were studied directly from gas exchanges using indirect calorimetry, after feeding moderate protein (MP; 35% energy) and high protein (HP; 52% energy) diets. Protein oxidation was significantly higher (P < 0.05) when cats were fed the HP diet (28.4 ± 0.7 mg/min) rather than the MP diet (20.4 ± 0.8 mg/min). Fat oxidation was significantly higher (P < 0.05) when cats consumed the MP diet (9.0 ± 0.7 mg/min) rather than the HP diet (4.7 ± 0.5 mg/min). Protein oxidation was significantly correlated (linear regression, R² = 46.0, P < 0.05) with protein intake such that the mean ratio of 18-h oxidation: 18-h intake was 1.2 on both diets. Fat oxidation was significantly correlated (linear regression, R² = 18.9, P < 0.05) with fat intake such that the mean ratio of 18-h fat oxidation: 18-h fat intake was 1.1 (MP) and 0.9 (HP). This study demonstrated that cats adapt net protein oxidation at these levels of protein intake, and the reason for the high dietary protein requirement of this species is, therefore, unclear.

KEY WORDS: • indirect calorimetry • fat oxidation • amino acid catabolism • carnivore • cats

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