The learnt phenotype: Physiological, behavioural and

Measuring the response of animals to environmental stimuli is a central component of assessing animal welfare. Host responses are usually considered to be governed through three interrelated modalities: physiology, behaviour and immune defence. Understanding how these responses are regulated is necessary before we can interpret what the responses tell us about the animal. The traditional view of regulation of physiological process is encompassed by the concept of homeostasis. This view holds that regulation occurs through feedback loops that drive physiological variables, for example, blood pressure or metabolite levels, towards a constant set point. More recently this model has been superseded by the concept of allostasis, which propses that regulation is a dynamic process that anticipates the predicted load on the host. For instance, the host learns though experience the oxygen demand of tissues associated with a particular pattern of exercise and elevates heart rate at the commencement of exercise before the need actually occurs for increased blood flow to the relevant tissues. Participation of the central nervous system in the processes of learning, prediction and subsequent dynami