As obligate carnivores, domestic cats rely on animal protein for their nutritional needs. The umami taste receptor (TAS1R1-TAS1R3) helps cats to detect nucleotides and amino acids that indicate sources of protein. However, some protein sources are characterised by an abundance of peptides, rather than free amino acids and nucleotides. Protein hydrolysates (peptones) are protein degradation products consisting largely of peptides. They are widely used within the pet food industry as both convenient sources of nutrition and for their role in palatability for cats. In this study we confirmed the positive taste response of cats to a peptone from animal tissue when dissolved in water and offered in a two-bottle choice test. Cats showed a significant preference for increasing concentrations of peptone solution (p < 0.0001) when 0.1% and 1% concentrations were compared to water and to each other. We also studied the response of the cat lysophosphatidic acid receptor 5 (cLPAR5, cGPR92) which has previously been shown to be expressed in the circumvallate papillae of mice and activated by peptones (but not by amino acids or nucleotides). We screened a library of 144 compounds against cLPAR5 when expressed in a heterologous assay system using CHO cells. The library included amino acids, nucleotides, fatty acids, biogenic amines, phospholipids, pyrophosphates, peptides, protein hydrolysates and pharmacological compounds. cLPAR5 was activated by 23 different compounds but only from the classes of phospholipids, pyrophosphates and peptones. The most potent stimulators of cLPAR5 by far were phospholipids, with EC50 values in the low micromolar to high nanomolar range. Peptones and pyrophosphates activated cLPAR5 at concentrations in the millimolar range.