Sulfur amino acid requirements and metabolism in cats

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Close to 40% of the Canadian population owns a cat (8.8 million in 2016) and there has been growth in Canadian cat food sales. Cats are obligate carnivores and animal proteins are used in large amounts to manufacture cat food. The availability and price of animal proteins may become constrained in the future as the human population increases and developing countries demand more animal-based proteins. While we have sufficient data to precisely feed many mono-gastric agricultural animals, our current knowledge of the indispensable amino acid (AA) requirements and broader effects of provision of AA on cats is woefully lacking. In general, outcomes of either growth or nitrogen balance have been used to measure AA requirements in growing cats, but no estimates in adult cats exist. Much less invasive carbon oxidation techniques, and more specially, the indicator AA oxidation (IAAO) technique have been used to empirically estimate AA requirements in many mammals. My laboratory estimated phenylalanine turnover in cats and these data suggest that orally dosing a tracer is a valid approach and small, frequent meals support a pseudo isotopic steady state. We have also validated behavioural acclimation to space restriction required to conduct respiratory gas collection and quantification in cats and applied these to measure energy metabolism and the net energy of different foods consumed by cats. Finally, I have applied the IAAO to estimate AA requirements and protein quality in pigs and dogs. My long term goals are to determine the requirement for the indispensable AA requirements of adult cats and understand how other dietary factors, such as dietary vitamins, may alter these. These data will lead to significant optimization in the delivery of protein to cats and reduce over supply of protein and AA in feline diets. The short-medium term goals of my program are to: 1. Measure the phenylalanine requirements when tyrosine is provided in excess to adult neutered male and female cats using the direct AA oxidation technique (Study 1)  2. Measure the methionine requirement when minimal cyst(e)ine is provided in adult castrated male and spayed female cats using the IAAO (Study 2) 2. Measure the methionine requirement when cysteine is provided in excess in adult castrated male and spayed female cats using the IAAO (Study 3)  3. Understand how the ratio of dietary methionine to cysteine alter transmethylation, remethylation and transsulfuration and contribute to the control synthesis of taurine and felinine in adult castrated male and spayed female cats using labeled methionine and cysteine tracers (Study 4) SIGNIFICANCE: The proposed studies will provide fundamental knowledge of sulfur AA requirements and how other nutrients affect sulfur AA requirements in domestic cats. When applied to cat food development, this knowledge will lead to more precise AA delivery, reduce excess provision of dietary protein, and support the health and well-being of cats.