Brains, quacks, and boojums: a review of neurotransmitter and neuroendocrine bases of welfare and enrichment in poultry with an emphasis on the Pekin duck.

In 1876, Lewis Carroll wrote The Hunting of the Snark in which he described a boojum as a particularly dangerous snark that if you found it, you would slowly disappear. In 1950, Dr. Franek Beach wrote The Snark was a Boojum in which he warned of the dangers of over interpreting physiological data related to behaviors. Today, we understand a great deal about the neurobiology of behavior, yet few have related this field to welfare. The purpose of this review is to provide an overview of this field as related to poultry and to point out some potential boojums. The Pekin duck, a major poultry product, is an important livestock species that requires further study to understand their physiological needs and welfare. Assessing welfare includes measuring physical, biological, and mental states of an animal and how it copes with its environment. There are many ways to improve animal welfare, one way is to provide environmental enrichment. Environmental enrichment varies among poultry species. Pekin ducks are waterfowl, so some believe that they should be allowed access to open water to increase positive natural behaviors and reduce unwanted behaviors. Beyond physical enrichment, another emerging approach is auditory enrichment, which has been extensively studied in zoo animals and is now gaining attention in livestock management. Vocalizations are a way to assess welfare and can be used as auditory enrichment. Birds use vocalizations as an effective way to communicate and can be used in various environmental conditions. This review highlights the established indicators for mental state, such as serotonin and dopamine, to validate methods of measuring affective state applied to environment changes. Neurotransmitter activity levels or turnover may be another physiological variable to determine affective state that is more reliable across age and sex. Similarly, gene expression can be linked to affective state by investigating the rate-limiting enzyme in serotonin and dopamine synthesis. Developing neuroendocrine profiles for poultry can elucidate how environmental changes affect physiology and welfare.