Dietary phenylalanine requirement of adult Labrador Retrievers using the direct oxidation approach

Abstract

Historically, the determination of amino acid (AA) requirements in dogs have been done in growing dogs and have been invasive in nature, requiring long periods of confinement and exposure to diets deficient in AA, which result in a reduction in the health and well being of dogs during the study period. Therefore, we were interested in examining whether carbon oxidation methods, with short periods of exposure to diets deficient in a single AA, could be successfully applied to determine AA requirements in dogs. Four adult Labrador Retrievers consumed 7 levels of phenylalanine (Phe), and excess tyrosine (Tyr) in random order and in combination with kibble that was formulated to be deficient in Phe and adequate in dietary energy (3730 kcal/kg as fed) and fed at ~13.5 g kg−1 BW d−1. Dogs were fed test diets for two days prior to conducting the tracer studies. The Phe requirement was determined by applying a 2‐phase linear regression crossover model to tracer oxidation (F13CO2). The mean Phe requirement was 3.27 g/kg diet (upper 95% CI= 4.96 g/kg diet) on a dry matter basis. The current NRC estimate of the adequate intake for Phe is 4.50 g/kg diet and based on growth and nitrogen balance in growing dogs. This magnitude of difference is similar to that seen when estimates of AA requirements in humans using nitrogen balance vs. carbon oxidation methods are compared.