PSX-A-17 - Late-Breaking: Methionine and total sulfur amino acid requirements for pups (>14 wk to 9 months), adults, and senior Labrador Retrievers using the indicator amino acid oxidation (IAAO) technique

Methionine and cystine are often considered limiting amino acids in canine diets but limited requirement studies have been conducted especially for different life stages. Eighteen Labrador Retrievers (6 pups ( >14 wk-9 month), 6 adults, and 6 seniors [ >8yr)] were utilized in feeding studies to evaluate the changing requirements of methionine (Met) and total sulfur amino acids (TSAA) as canines age. For this study, the indicator amino acid oxidation (IAAO) technique was utilized to determine the amino acid (AA) requirements in each of the three age groups. Dogs were subjected to diets ranging from deficient to excess, with indispensable amino acids formulated at 1.6x NRC values. To allow for adaptation, a control diet with same dietary ingredients, protein and amino acid levels was fed for two days prior to feeding the test diets on the third day. On test day, a baseline breath sample was collected for determining CO2 production using a respiration mask (Oxymax, Columbus Instruments). A priming dose of L-[1-¹³C] phenylalanine (Cambridge Isotope Laboratories, Inc.) based on body weight was utilized, followed by [1-¹³C] Phe doses every 30 minutes, spanning a four hour period. After each dose ¹³CO₂ was collected, and enrichment was determined by isotope ratio mass spectrometry (IRMS). Results for IRMS were converted to atom percent excess (APE) and analyzed using a piecewise model of best fit (JMP^® Pro 16). A segmented line regression showed Met and TSAA mean and population requirements for pups ( >14 wk-9 mo.) were 0.78 ± 0.16 and 1.53 ± 0.21 g/1000kcal (mean ± 2SD), respectively. Meanwhile, for adults, mean and population requirements for Met and TSAA were estimated to be 0.68 ± 0.19 and 1.4 ± 0.30 g/1000kcal (mean ± 2SD), respectively, and for seniors, Met and TSAA mean and population requirements were determined to be 0.62 ± 0.17 and 1.27 ± 0.23 g/1000kcal (mean ± 2SD), respectively.