Animal well-being. III. An overview of assessment.

Assessment of animal well-being is a complex matter. It is difficult to establish a causal link between stimuli and internal state because of numerous variables and the time interval between cause and effect. Many studies document a correlation rather than a causal relationship among stimuli, responses, and subsequent health, disease, or mental state. Research objectives are often vague, the choice of assessment parameters is perplexing, and the results are difficult to interpret. In general, animal well-being cannot be assessed directly. There are no standardized methods or specific endpoints that provide an objective determination. Overt changes in physical and psychological functions occur only after the animal has experienced a prepathologic state. An animal's response to general arousal, life's events, and aversive stimuli depends on an integrated activation of various neural and endocrine factors. A variety of physiologic, biochemical, and behavioral characteristics change when an animal is exposed to aversive situations and stimuli, although many also change with the onset of positive general arousal, such as play, pleasant experiences, and sexual excitement. There is a need to evaluate numerous criteria (e.g., performance, clinical state, neurochemistry, endocrinology, immunology, morphology, behavior, and ethology) to compile a complete mental and biological profile of animals. The various systems, processes, and individual specific responses are interrelated and interact in a well-structured manner. Given the complexity of the topic and the disparate disciplines involved, developing a comprehensive understanding of animal well-being is not straightforward. Consequently, observers should be cautious. Foremost in any determination of animal well-being is assurance that criteria being used are relevant to well-being.