106 - Minimum Methionine Requirement in Adult Cats Using the Indicator Amino Acid Oxidation Technique

Abstract: Despite the importance of Met for protein synthesis and a wide range of metabolic functions, little is known about its requirement in adult cats. Current recommendations for adult cats are based solely on studies using kittens and growth or nitrogen balance as the outcomes. Thus, this study aimed to determine the minimum Met requirement in mature cats using the indicator amino acid oxidation (IAAO) technique. Four adult neutered male cats (4.90 + 0.77 kg BW) were used in a Latin rectangle design. Cats were fed a semi-synthetic diet sufficient in Met for 2 weeks prior to being randomly allocated to one of the eight dietary Met treatments (0.12%, 0.17%, 0.21%, 0.28%, 0.35%, 0.42%, 0.50% and 0.57% dry-matter). Cys was provided in excess to spare the Met requirement and meet the Cys requirement. After 2d of adaptation, individual IAAO studies were performed. During each IAAO study day, cats were placed in indirect calorimetry chambers and fed 75% of their daily ration (12.38g/kg BW) split in 13 ½-hourly small meals. A priming dose of NaH¹³CO₃ (0.44mg/kg) and L-[1-¹³C]-Phe (4.8mg/kg) were provided in the 4^th and 5^th meal, respectively, following by a constant dose (1.04mg/kg) of L-[1-¹³C]-Phe in the next meals. Breath samples were collected ½-hourly to measure ¹³CO2 enrichment to quantify ¹³CO₂ and calculate F¹³CO₂ during isotopic steady state (Phe oxidation). Competing models, broken-line linear (BLL) ascending model, and a broken-line quadratic (BLQ) ascending model, were fitted on F¹³CO₂ to determine the minimum requirement of Met (breakpoint). The BLL yielded the best model with mean minimum Met requirement estimated at 0.305% (dry-matter), and the 95% confidence interval estimated at 0.521% (dry-matter) for adult cats. In conclusion, the estimated min Met requirement in this study is greater than those currently recommended by the NRC (2006; 0.17% dry-matter) and AAFCO (0.2% dry-matter).