Kokumi taste is a well-accepted and characterised taste modality and is described as a sensation of enhancement of sweet, salty, and umami tastes. The Calcium Sensing Receptor (CaSR) has been designated as the putative kokumi taste receptor for humans, and a number of kokumi-active ligands of CaSR have been discovered recently with activity confirmed both in vivo and in vitro. Domestic cats (Felis catus) are obligate carnivores and accordingly, their diet is abundant in proteins, peptides, and amino acids. We hypothesised that CaSR is a key taste receptor for carnivores, due to its role in the detection of different peptides and amino acids in other species. Using in silico, in vitro and in vivo approaches, here we compare human CaSR to that of a model carnivore, the domestic cat. We found broad similarities in ligand specificity, but differences in taste sensitivity between the two species. Indeed our in vivo data shows that cats are sensitive to CaCl₂ as a kokumi compound, but don’t show this same activity with Glutathione, whereas for humans the reverse is true. Collectively, our data suggest that kokumi is an important taste modality for carnivores that drives the palatability of meat-derived compounds such as amino acids and peptides, and that there are differences in the perception of kokumi taste between carnivores and omnivores.

The domestic cat (Felis catus) is an obligate carnivore, and as such has a meat-based diet. Several studies on the taste perception of cats have been reported, indicating that their sense of taste has evolved based on their carnivorous diet. Here, we propose that umami (mediated by Tas1r1-Tas1r3) is the main appetitive taste modality for the domestic cat by characterizing the umami taste of a range of nucleotides, amino acids, and their mixtures for cats obtained using complementary methods. We show for the first time that cats express Tas1r1 in taste papillae. The cat umami receptor responds to a range of nucleotides as agonists, with the purine nucleotides having the highest activity. Their umami receptor does not respond to any amino acids alone; however, 11 l-amino acids with a range of chemical characteristics act as enhancers in combination with a nucleotide. l-Glutamic acid and l-Aspartic acid are not active as either agonists or enhancers of the cat umami receptor due to changes in key binding residues at positions 170 and 302. Overall, cats have an appetitive behavioral response for nucleotides, l-amino acids, and their mixtures. We postulate that the renowned palatability of tuna for cats may be due, at least in part, to its specific combination of high levels of inosine monophosphate and free l-Histidine that produces a strong synergistic umami taste enhancement. These results demonstrate the critical role that the umami receptor plays in enabling cats to detect key taste compounds present in meat.

Domesticated cats have evolved from the obligate carnivore Felis silvestris. The instinct to eat small frequent meals and a crepuscular feeding rhythm was conserved during domestication. Declining senses, cognitive impairment, and poor oral health decrease food intake in aging cats. Combined with metabolic and physiological changes, they are at risk of sarcopenia and general body condition impairment. Aging cats may, therefore, benefit from modified nutritional strategies to achieve their metabolic energy requirements; however, little is known about feeding patterns in aging cats and influence of food format. This in-home study of 134 aging cats (≥7 years) assessed ad libitum dry, wet, and wet/dry (‘mixed’) feeding regimens to compare 24 h feeding frequency and caloric intakes. Feeding frequency was significantly different between wet and dry (p = 0.02) and mixed and dry diets (p < 0.001), with cats consuming 6.0 (dry), 6.9 (wet), or 7.2 meals (mixed) per day. Mean caloric intakes were significantly higher for dry (262.6 kcal/d) and mixed (222.6 kcal/d) regimens (both p < 0.001) versus wet (138.1 kcal/d). In conclusion, healthy aging cats eat small frequent meals, with feeding frequency and caloric intake influenced by dietary format. These findings support development of evidence-based feeding guidelines for aging cats.

Dogs, domesticated from gray wolves over 15,000 yr ago, exhibit extensive variation among breeds, including differences in olfactory ability. To investigate the genetic basis of these differences, we analyzed single-nucleotide variants (SNVs) in 3 chemosensory receptor gene families—olfactory receptors (ORs), vomeronasal receptors type 1 (V1Rs), and bitter taste receptors (T2Rs)—using whole-genome data from the Dog Biomedical Variant Database Consortium, which includes 635 domestic dogs representing 121 breeds and 8 wolves. We identified 179 segregating pseudogenes in OR genes (minor allele frequency > 1%), including cases where intact genes are pseudogenized in some individuals and vice versa. The number of functional OR genes varied substantially among individuals (779 to 807), while V1R and T2R gene counts were nearly invariant (8 and 16, respectively). Compared to wolves, dogs exhibited significantly higher ratios of nonsynonymous to synonymous SNVs (N/S) in OR and T2R genes, suggesting relaxed functional constraints potentially associated with domestication. Among breeds, Pugs had significantly fewer functional OR genes and a higher N/S ratio than other breeds, even after accounting for copy number variation. Notably, an OR gene orthologous to the human androstenone receptor, OR7D4, was completely pseudogenized in all Pugs but remained largely functional in other breeds. These findings support the hypothesis that reduced olfactory ability in brachycephalic breeds, such as Pugs, is associated with genetic degeneration of OR genes. Overall, our study provides new insights into the genetic diversity of chemosensory receptor repertoires in dogs and underscores the impact of domestication and breed-specific morphological traits on olfactory function.