PSX-7 - Determination of tryptophan requirements of adult and senior Labrador retrievers using the indicator amino acid oxidation technique

Abstract: Nutritional requirements vary across the life stages of canines, and the consumer demand for advanced diets that meet the age-appropriate needs of their pets has steadily increased. Availability of veterinary care and high-quality nutrition has led to a longer average lifespan in companion animals, and although senior dogs represent a significant proportion of the pet population, few studies have targeted the specific amino acid requirements of the aging canine. In this study, the indicator amino acid oxidation (IAAO) technique was used to compare the tryptophan (Trp) requirements of young adult and senior Labrador retrievers. After 2-day adaptation to Trp-adequate basal diet (Trp= 0.256% dry matter), dogs underwent individual IAOO studies. In brief, all dogs were randomly fed one of six test diets with varying levels of tryptophan ranging from deficient to sufficient (final Trp content in experimental diets was 0.05, 0.1, 0.15, 0.224, 0.25 and 0.256% dry matter. Test diet was divided into 13 equal meals; at the 5th meal, a tracer amino acid was supplied (a bolus L-[1-¹³C]phenylalanine based on body weight was first given, followed by [1-¹³C]Phe doses every thirty minutes spanning a four-hour period), and breath samples were collected via respiration mask every thirty minutes. Total production of ¹³CO₂ during isotopic steady state was determined by enrichment of ¹³CO₂ in breath samples and total CO₂ production measured via indirect calorimetry and isotope ratio mass spectrometry (IRMS). Results for IRMS were converted to atom percent excess (APE) and analyzed using segmented linear regression. The Four Rivers mean and population requirements for tryptophan were 377.7 ± 31.9 mg/1000 kcal ME (mean ± 2SD) in the young adults and 362.9 ± 31.5 mg/1000 kcal ME for senior dogs, which are higher than the currently recommended amounts by NRC and AAFCO. As the petfood industry offers more specialized diets for aging canines, updating the amino acid requirements for such animals is increasingly important.