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

Drivers of Palatability for Cats and Dogs-What It Means for Pet Food Development

The pet food industry is an important sector of the pet care market that is growing rapidly. Whilst the number of new and innovative products continues to rise, research and development to assess product performance follows traditional palatability methodology. Pet food palatability research focuses on the amount of food consumed through use of one-bowl and two-bowl testing, but little understanding is given to why differences are observed, particularly at a fundamental ingredient level. This review will highlight the key differences in feeding behaviour and nutritional requirements between dogs and cats. The dominant pet food formats currently available and the ingredients commonly included in pet foods are also described. The current methods used for assessing pet food palatability and their limitations are outlined. The opportunities to utilise modern analytical methods to identify complete foods that are more palatable and understand the nutritional factors responsible for driving intake are discussed.

The Neurobiology of Behavior and Its Applicability for Animal Welfare: A Review

Simple Summary

Animal welfare is the result of physical and psychological well-being and is expected to occur if animals are free: (1) from hunger, thirst and malnutrition, (2) from discomfort, (3) from pain, (4) to express normal behavior, and (5) from fear and distress. Nevertheless, well-being is not a constant state but rather the result of certain brain dynamics underlying innate motivated behaviors and learned responses. Thus, by understanding the foundations of the neurobiology of behavior we fathom how emotions and well-being occur in the brain. Herein, we discuss the potential applicability of this approach for animal welfare. First, we provide a general view of the basic responses coordinated by the central nervous system from the processing of internal and external stimuli. Then, we discuss how those stimuli mediate activity in seven neurobiological systems that evoke innate emotional and behavioral responses that directly influence well-being and biological fitness. Finally, we discuss the basic mechanisms of learning and how it affects motivated responses and welfare.

Abstract

Understanding the foundations of the neurobiology of behavior and well-being can help us better achieve animal welfare. Behavior is the expression of several physiological, endocrine, motor and emotional responses that are coordinated by the central nervous system from the processing of internal and external stimuli. In mammals, seven basic emotional systems have been described that when activated by the right stimuli evoke positive or negative innate responses that evolved to facilitate biological fitness. This review describes the process of how those neurobiological systems can directly influence animal welfare. We also describe examples of the interaction between primary (innate) and secondary (learned) processes that influence behavior.

Preference and discrimination of facial expressions of humans, rats, and mice by C57 mice

Social animals likely recognize emotional expressions in other animals. Recent studies suggest that mice can visually perceive emotional expressions of other mice. In the first experiment, we measured the preference of mice for two different facial expressions (a normal facial expression and an expression of negative emotion such as pain) of rats, mice, and humans. Results revealed that mice showed a slight preference for the normal expression over the face expressing pain in the case of rats, but no preference in the case of others. In the second experiment, we trained mice to discriminate between the two facial expressions in an operant chamber with a touch screen. They could discriminate facial expressions of mice and rats, but they did not show discrimination of human facial expressions. Principal component analysis of the images of stimuli reveals negative correlation between pixel-based dissimilarity of training stimuli and the number of sessions to criterion. The mice showed generalization to novel images of the mouse faces with and without pain but did not maintain their discriminative behavior when new rat faces were shown. These results suggest that mice display category discrimination of conspecific facial expressions but not of other species.

Vegan versus meat-based pet foods: Owner-reported palatability behaviours and implications for canine and feline welfare

Consumer suspicion of conventional pet foods, along with perceived health benefits of alternative diets, are fuelling development of the latter. These include raw meat diets, in vitro meat products, and diets based on novel protein sources such as terrestrial and marine plants, insects, yeast and fungi. However, some claim vegan diets may be less palatable, or may compromise animal welfare. We surveyed 4,060 dog or cat guardians to determine the importance to them of pet food palatability, and the degree to which their animals displayed specific behavioural indicators of palatability at meal times. Guardians were asked to choose one dog or cat that had been within their household for at least one year, and not on a prescription or therapeutic diet. Of 3,976 respondents who played some role in pet diet decision-making, palatability was the third most important among 12 factors cited as important when choosing pet diets. For 1,585 respondents feeding conventional or raw meat diets, who stated they would realistically consider alternative diets, palatability was the fourth most important among 14 desired attributes. For the 2,308 dogs included, reported observations of 10 behavioural indicators of palatability at meal times reliably indicated significant effects of increased reports of appetitive behaviour by dogs on a raw meat diet, as opposed to a conventional diet. There was no consistent evidence of a difference between vegan diets and either the conventional or raw meat diets. For the 1,135 cats included, reported observations of 15 behavioural indicators indicated that diet made little difference to food-oriented behaviour. Based on these owner-reported behaviours, our results indicate that vegan pet foods are generally at least as palatable to dogs and cats as conventional meat or raw meat diets, and do not compromise their welfare, when other welfare determinants, such as nutritional requirements, are adequately provided.

Taste-induced facial responses in black-handed spider monkeys (Ateles geoffroyi)

Taste-induced facial expressions are thought to reflect the hedonic valence of an animal's gustatory experience. We therefore assessed taste-induced facial responses in six black-handed spider monkeys (Ateles geoffroyi) to water, sucrose, caffeine, citric acid and aspartame, representing the taste qualities sweet, bitter, and sour, respectively. We decided not to include salty-tasting substances as the concentrations of such tastants found in the fruits consumed by spider monkeys are below their taste preference threshold. We found that the monkeys displayed significant differences in their facial responses between substances, with significantly higher frequencies of licking, sucking, closed eyes, tongue protruding, mouth gaping and lip smacking in response to sucrose, a presumably pleasant stimulus. The response to caffeine and citric acid, in contrast, yielded the lowest frequencies of these behaviors, but the highest frequency of withdrawals from the stimulus, suggesting these substances are perceived as unpleasant. Lip stretching, a newly described behavior, was performed significantly more often in response to caffeine than to any other substance, suggesting an association with the response to bitter taste. The facial response to the artificial sweetener aspartame was generally similar to the response to water, corroborating the notion that Platyrrhines may be unable to detect its sweetness. Overall, the present study supports the idea of similarity of taste-induced facial responses in non-hominoid primates and humans, suggesting these displays to be evolutionarily conserved across the primate order.

Multisensory and Motor Representations in Rat Oral Somatosensory Cortex

In mammals, a complex array of oral sensors assess the taste, temperature and haptic properties of food. Although the representation of taste has been extensively studied in the gustatory cortex, it is unclear how the somatosensory cortex encodes information about the properties of oral stimuli. Moreover, it is poorly understood how different oral sensory modalities are integrated and how sensory responses are translated into oral motor actions. To investigate whether oral somatosensory cortex processes food-related sensations and movements, we performed in vivo whole-cell recordings and motor mapping experiments in rats. Neurons in oral somatosensory cortex showed robust post-synaptic and sparse action potential responses to air puffs. Membrane potential showed that cold water evoked larger responses than room temperature or hot water. Most neurons showed no clear tuning of responses to bitter, sweet and neutral gustatory stimuli. Finally, motor mapping experiments with histological verification revealed an initiation of movements related to food consumption behavior, such as jaw opening and tongue protrusions. We conclude that somatosensory cortex: (i) provides a representation of the temperature of oral stimuli, (ii) does not systematically encode taste information and (iii) influences orofacial movements related to food consummatory behavior.