Palatability: principles, methodology and practice for farm animals.

Abstract Palatability is a complex concept, not amenable to concise definition because it depends not only on the organoleptic properties of the food but also on the experience and genetic background of the animal in question and its physiological state, as well as environmental conditions and social context. The learning of the association between the appearance, flavour or texture of a food and the metabolic consequences of eating that food provides the animal with a conditioned response to that food, either preference or aversion, irrespective of the nature of the sensory cue. Some flavours are innately preferred, others aversive, but conditioning can change these preferences. Critical to the understanding of palatability is an appreciation of the methods used to measure it. These range from the initial rate of eating of a food, through choices expressed between two (or more) foods offered simultaneously, to more sophisticated methods involving direct or operant conditioning. Many factors influence the outcome of palatability tests, including the length of the test, time of the day, sensory characteristics of foods, environmental factors, physiological state of the animal and opportunity to learn from conspecifics. Whether or not long-term intake can be predicted from short-term preference depends on how the latter is measured and whether the animals have innate or conditioned preferences for a food; thus, detailed knowledge of the animals' history and the conditions under which a test has been carried out is necessary in order to interpret and make use of palatability measurements.