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Where's Waldo? Using sickness behavior to find the sick animal in the crowd
The ability to find sick animals in a group can be challenging for people in charge of caring for animals. Specifically, in food animal agriculture sick animals are frequently recognized as ill by vague signs of physical and behavioral changes that are described as animals being dull or off. While some people can use these signs effectively, these signs are difficult to quantify and are difficult to train people unfamiliar with ‘normal’ animals to identify. In order to better identify sick animals in groups sickness behavior represents an avenue to facilitate early disease detection, animal handlers can be trained in detection sooner, and environments can be designed to improve recovery through supporting animals natural defenses against disease during convalescence.
Hart first described sickness behavior as a strategic evolved response rather than a maladaptive response to infection in 1988. In this paper Hart described characteristics that were consistent across species as indicators of illness- lethargy, anorexia, depression and febrile. The next great leap forward in occurred in 1999 when Aubert published his hypothesis that the behaviors described by Hart and other researchers were motivational in nature and as such, could be suspended in cases where sickness behavior conflicts with activities that are essential for short-term survival, care of offspring, and in some cases reproduction. Since 1999, there has been continued research into increasing our knowledge of the function and causation of sickness behaviors. However, aspects of this information are only recently being used on farms to identify sick animals in a group.
The lack of species specific indicators of these behaviors has limited the use of sickness behavior for disease detection. While sickness impacts similar changes in the motivation to perform behavior across species, the species specific indicators of how these changes can be identified is still in its infancy. As animal agriculture has expanded the more obvious behavior changes of decreased feed and water intake become more difficult to detect at the individual level. By understanding sickness behavior and identifying species specific behaviors sick animals can be identified sooner, appropriate technology can be utilized to measure changes, training of animal handlers can be improved, and housing environments can be altered to suit the needs of the animals during convalescence.
Keywords: sickness behavior, health, management