Facial expressions and other behavioral responses to pleasant and unpleasant tastes in cats (Felis silvestris catus)

- Cats display distinct facial expressions to pleasant and unpleasant tastes.
- No masking effect of a pleasant taste on an unpleasant taste was observed.
- Behavioral responses may be more informative than consumption data concerning taste.

The goal of the present study was to assess how cats react to tastes previously reported to be preferred or avoided relative to water. To this end, the facial and behavioral reactions of 13 cats to different concentrations of l-Proline and quinine monohydrochloride (QHCl) as well as mixtures with different concentrations of the two substances were assessed using a two-bottle preference test of short duration. The cats were videotaped and the frequency and duration of different behaviors were analyzed. Significant differences in the cats' behavior in response to the taste quality of the different solutions included, but were not limited to, Tongue Protrusions (p < 0.039), Mouth smacks (p = 0.008) and Nose Licks (p = 0.011) with four different stimulus concentrations. The cats responded to preferred taste by keeping their Eyes half-closed (p = 0.017) for significantly longer periods of time with four different stimulus concentrations compared to a water control. When encountering mixtures containing l-Proline and QHCl the cats performed Tongue protrusion gapes (p < 0.038) significantly more frequently with three different stimulus concentrations compared to an l-Proline control. A stepwise increase in the concentration of l-Proline from 5 mM to 500 mM in mixtures with 50 μM QHCl did not overcome the negative impact of the bitter taste on intake. The results of the present study suggest that behavioral responses provide an additional dimension and may be more informative than consumption data alone to assess whether cats perceive tastes as pleasant or unpleasant. Thus, the analysis of behavioral responses to different taste qualities may be a useful tool to assess and improve the acceptance of commercial food by cats.