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Adaptation to Amino Acid Kinetics and Urea Production in Adult Cats (Felis catus) Fed Below Their Protein Requirement (P09-008-19).

Objectives
Cats are obligate carnivores that evolved eating meat-based diets and have high requirements for amino acids (AA). However, little is known about how they regulate AA metabolism, especially at intakes below their requirement. This study was undertaken to examine the effect of dietary protein level above and below their requirement on urea production and AA metabolism in cats.


Methods
Cats (n = 18) were allocated to three treatments (7.5, 15, or 40% ME intake as crude protein), fed at maintenance for 3 wk, and then fitted with saphanous and cephalic vein catheters. On the following day, they received primed continuous infusions of [13C]bicarbonate, [1-13C]Leu and [15N2]urea from 0 to 120, 120 to 480 and 0 to 480 min, respectively. Cats were fed hourly during infusion and Leu entry rate from diet was calculated. Breath was sampled at 0, 100, 110, 120, 440, 460, and 480 min to measure 13CO2, with blood sampled at 0, 440, 460, and 480 min to measure 13C enrichments in Leu and ketoisocaproate, and [15N2]urea.


Results
Values for non-oxidative Leu disposal (NOLD, an indicator of protein synthesis), Leu rate of appearance in plasma (Ra, an indicator of protein degradation), Leu oxidation, and urea production rate (an indicator of net protein catabolism) are shown in Table 1. There were no differences in any measurements in cats fed at (15%) or below (7.5%) their requirement for protein. However, those fed with 7.5% of ME intake as crude protein had numerically lowest rates of whole body AA catabolism and oxidation, whereas, Leu Ra was numerically greatest.


Conclusions
Using Leu kinetics to trace AA metabolism, there did not seem to be a difference between cats fed at or below their requirement for protein. This may indicate that cats are able to adapt to dietary protein content more than what was previously believed.


Funding Sources
Massey University Research Fund, and the McGeorge Research Fund.


Supporting Tables Images and/or Graphs