PSXIII-B-3 - Determining Phenylalanine and Tyrosine Amino Acid Requirements in Growing Labrador Retrievers Using the Direct Amino Acid Oxidation Technique

Abstract: Phenylalanine and tyrosine are important amino acids for synthesis of proteins, catecholamine neurotransmitters, and melanin in canines. Since phenylalanine (Phe) is converted to tyrosine (Tyr), this experiment used the direct amino acid oxidation (DAAO) technique to determine the phenylalanine requirement and phenylalanine plus tyrosine requirements for growing Labrador Retrievers. The Phe requirement was separated from Phe plus Tyr requirement by supplementing the test diets utilized for Phe requirements with 1.48% crystalline Tyr. A total of twelve dogs were used in two trials to determine the Phe and Phe + Tyr requirements in growing puppies ( >14wk-1yr). Control diet was fed for two days, followed by a testing day where an experimental diet was fed, a tracer amino acid was supplied, and breath samples were collected. On test day, a priming dose of L-[1-¹³C] phenylalanine (Cambridge Isotope Laboratories, Inc.) based on the dog’s body weight was supplied, followed by enteral feeding of [1-¹³C]Phe every 30 minutes, spanning a four hour period. Respiration masks were placed on each subject every 30 minutes (Oxymax, Columbus Instruments), ¹³CO₂ collected, and enrichment determined by isotope ratio mass spectrometry (IRMS). Results for IRMS were converted to atom percent excess (APE) and analyzed using a segmented model (JMP^® Pro 15). Results showed that Phe mean and population safe requirements were 1.29 +/- 0.26 g/1000 kcal, while the Phe + Tyr requirements were 1.95 +/- 0.65 g/1000 kcal. Knowledge gathered through these studies is invaluable as both the Phe and Phe plus Tyr dietary requirements for growing Labrador Retriever puppies were determined.