Amino Acid Oxidation Increases with Dietary Protein Content in Adult Neutered Male Cats as Measured Using [1-13C]Leucine and [15N2]Urea.
BACKGROUND
Cats are unique among domestic animals in that they are obligate carnivores and have a high protein requirement. However, there are few data on protein turnover and amino acid (AA) metabolism in cats.


OBJECTIVE
The aim of this study was to examine the effects of dietary protein content on urea production and Leu metabolism in cats.


METHODS
Eighteen neutered male cats (4.4 ± 0.11 kg body weight, aged 4.6 ± 0.41 y) fed to maintain body weight for 3 wk with 15%, 40%, or 65% metabolizable energy intake as crude protein (CP) had [1-(13)C]Leu administered in the fed state. Urea production was measured by the infusion of [(15)N2]urea. Leu flux, nonoxidative Leu disposal (NOLD; protein synthesis), Leu rate of appearance (Ra; protein degradation), and Leu oxidation were determined.


RESULTS
Urea production and Leu oxidation were both ∼ 3 times greater in cats fed 65% CP compared with those fed 15% CP, whereas those fed 40% CP were ∼ 1.6 times greater (P < 0.05). Leu flux was 1.9 and 1.3 times greater in cats fed 65% CP compared with those fed 15% and 40% CP (P < 0.001). Almost 39% of total Leu flux was oxidized by cats fed 15% CP, whereas this increased to 58% in cats fed 65% CP (P < 0.002). There were no differences for Ra, but cats fed 65% CP tended to have 30% greater NOLD (P = 0.09) and to be in positive protein balance (P = 0.08) compared with those fed 15% CP.


CONCLUSIONS
The high protein requirement of cats combined with a low rate of whole-body protein synthesis ensures that an obligate demand of AAs for energy or glucose (or both) can be met in an animal that evolved with a diet high in protein with very little or no carbohydrate.
Monogastric Research Centre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand; and t.j.wester@massey.ac.nz.
Timothy J
TJ
Wester
Monogastric Research Centre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand; and.
Karin
K
Weidgraaf
Monogastric Research Centre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand; and.
Margreet
M
Hekman
Monogastric Research Centre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand; and.
Claudia E
CE
Ugarte
Monogastric Research Centre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand; and.
Sandra F
SF
Forsyth
Animal Nutrition and Health Group, AgResearch Grasslands Ltd., Palmerston North, New Zealand.
Michael H
MH
Tavendale
D000596:Amino Acids / Q000097:blood* / Q000378:metabolism*; D000821:Animal Feed / Q000032:analysis; D000818:Animals; D001835:Body Weight; D002415:Cats; D004032:Diet / Q000662:veterinary*; D004044:Dietary Proteins / Q000008:administration & dosage*; D002149:Energy Intake; D007930:Leucine / Q000097:blood*; D008297:Male; D010084:Oxidation-Reduction; D010865:Pilot Projects; D014508:Urea / Q000097:blood*
D000596:Amino Acids; D004044:Dietary Proteins; D014508:Urea; D007930:Leucine
Felis catus; carnivore; precursor method; protein metabolism; protein turnover; urea