Measurement of whole body protein turnover in the adult cat ( Felis catus )

There are few data on protein turnover in the domestic cat, which as an obligate carnivore, has a higher protein requirement than omnivores and herbivores. In the current study, kinetics of [1– 13 C]leucine metabolism was used to quantify rates of whole body protein synthesis, degradation, and oxidation in adult cats adapted to a commercial 45% crude protein diet at maintenance. Five female domestic short‐hair cats were fasted overnight before receiving a primed continuous infusion of [1– 13 C]leucine into the cephalic vein for 6 h. Blood and breath were sampled in the last hour of infusion. Isotopic enrichment of leucine and α‐ketoisocaproic acid in plasma and CO 2 in expired breath were measured. Basal CO 2 excretion was measured from a 2‐h primed continuous infusion of [ 13 C]NaCO 3 prior to the leucine infusion. Values (mean ± SE) for leucine flux, non‐oxidative leucine disposal (i.e., leucine disposal into protein), and leucine oxidation were 310 ± 10.7, 114 ± 10.3, and 196 ± 7.8 μmol/(kg body weight/hour), respectively. Non‐oxidative leucine disposal is an indication of whole body protein synthesis, and when intake is = 0 (i.e., fasted) flux represents appearance of leucine from body protein, an indication of whole body protein breakdown. Using the fraction of leucine present in the lean body mass of female cats, values for protein breakdown, synthesis, and balance were 13.4 ± 0.46, 8.48 ± 0.33, and −4.92 ± 0.45 g/(kg bodyweight/d), respectively. The [1– 13 C]leucine method proved to be a relatively simple method to determine whole body protein turnover in cats. Research supported by the Massey University Research Fund.