Methods of identifying canine subjects having an increased likelihood of developing elevated levels of 4-ethylphenyl sulfate, canine stress, canine anxiety and/or an inhibition of growth of beneficial microbes and promotion of growth of harmful microbes are disclosed. Methods comprise analyzing a biological sample obtained from the canine subject for the presence of two copies of a minor allele of the single nucleotide polymorphism BICF2P1175095 in a canine subject. Methods of treating the identified canine subjects by administering an effective amount of tomato pomace are also disclosed. Methods of treating canine subjects for elevated 4-EPS levels, canine anxiety or canine stress are disclosed. Canine food compositions that comprises tomato pomace are disclosed.