Lowry, Lou Anne2022-09-262022-09-262022http://hdl.handle.net/10179/17589The domestic cat, an obligate carnivore, evolved eating a diet rich in protein. Their high protein requirement ensures an adequate supply of amino acids (AA) for metabolism even though AA are relied on for energy. However, there is little research examining AA use at intakes below their protein requirement. The first objective investigated AA kinetics using the [1-¹³C]Leu precursor method in cats fed above, at, and below their protein requirement. The second objective measured hepatic protein synthesis using a modified D₂O method, which when in conjunction with Objective 1, allowed direct comparison of hepatic protein synthesis with whole-body synthesis. Domestic short-hair cats (n=18) from the Massey University Centre for Feline Nutrition were fed to maintain body weight on diets containing 7.5, 15, and 40% of metabolizable energy as crude protein (CP). After 3 wk, [¹³C]Na bicarbonate and [¹⁵N₂]Urea were infused into a cephalic vein while in the fed state. After 2 h, bicarbonate was switched to [1-¹³C]Leu, and ²H₂0 was administered as a subcutaneous bolus to label body water. Blood and breath were sampled after 0, 100, 110, 120, 440, 460, and 480 minutes after start of infusions. Deuterium enrichment in free and albumin-bound Ala was measured to estimate hepatic protein synthesis. Non-oxidative Leu disposal (representing protein synthesis) was not different among treatments. Leu rate of appearance in plasma (representing protein degradation) was nearly 1.5X greater in cats fed 7.5 and 15% CP (P < 0.05) than in those fed 40% CP. Leu oxidation was greatest in cats fed 40% CP (P < 0.01), but did not differ for cats fed at or below their requirement, despite oxidation in cats fed 15% CP tending to be 20% greater than those fed 7.5% CP. Results for urea production (representing net AA catabolism) mirrored those for Leu oxidation. Values for hepatic protein synthesis proved unreliable, possibly due to errors in administration of D₂O. To conclude, AA oxidation in cats fed below their protein requirement did not decrease compared to those fed at requirement. This suggests that the cat is unable to down regulate AA oxidation when protein requirements are low.enThe AuthorThesis300303 Animal nutrition