Volume 89, Issue 1, January (2003), pp. 29-37 © The Author 2003
doi:10.1079/BJN2002735

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Whole-body protein turnover of a carnivore, Felis silvestris catus

K. Russell^1*, G. E. Lobley² and D. J. Millward^3
1Waltham Centre for Pet Nutrition, Melton Mowbray LE14 4RT, UK
²Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, UK
³School of Biomedical and Life Sciences, University of Surrey, Guildford GU2 5XH, UK

 (Received 28 November 2001–Revised 16 July 2002–Accepted 15 August 2002)

The cat (Felis silvestris catus) has a higher dietary protein requirement than omnivores and herbivores, thought to be due to metabolic inflexibility. An aspect of metabolic flexibility was examined with studies of whole-body protein turnover at two levels of dietary protein energy, moderate protein (MP; 20 %) and high protein (HP; 70 %), in five adult cats in a crossover design. Following a 14 d pre-feed period, a single intravenous dose of [¹⁵N]glycine was administered and cumulative excretion of the isotope in urine and faeces determined over 48 h. N flux increased (P<0·005) with dietary protein, being 56 (se5) mmol N/kg body weight ( BW) per d for cats fed the MP diet and 146 (se 8) mmol N/kg BW per d for cats fed the HP diet. Protein synthesis was higher (P<0·05) on the HP diet (75 (se 10) mmol N/kg BW per d; 6·6 (se 1) g protein/kg BW per d) than the MP diet (38 (se 5) mmol N/kg BW per d; 3·4 (se 0·4) g protein/kg BW per d). Protein breakdown was higher (P<0·05) on the HP diet (72 (se 8) mmol N/kg BW per d; 6·3 (se 0·7) g protein/kg BW per d) than the MP diet (44 (se 3) mmol N/kg BW per d; 3·9 (se 0·3) g protein/kg BW per d). Compared with other species the rate of whole-body protein synthesis in the well-nourished cat (9·7 (se 1·3) g protein/kg BW^0·75 per d) is at the lower end of the range. These results show that feline protein turnover adapts to dietary protein as has been shown in other species and demonstrates metabolic flexibility. Further work is required to determine exactly why cats have such a high protein requirement.

*Corresponding author: Miss Kim Russell, fax +44 1664 415 440, email kim.russell@eu.effem.com

Keywords:
Cat: Nitrogen: [¹⁵N]glycine endproduct method: Protein metabolism: Protein intake