ILAR Journal Online, Volume 39(1) 1998: Animal Well-being: Immune Function, Behavior, Morphology, and Psychoneuroimmunology

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ILAR Journal V39(1) 1998
Animal Well-being: Immune Function, Behavior, Morphology, and Psychoneuroimmunology

Introduction
J. Derrell Clark

Although the term "animal well-being" has become prominent in the vocabulary of scientists and others concerned about animal care and use, the concepts behind the term are unclear. Frequently asked questions are

What is animal well-being?
Why is there concern about animal well-being?
What determines well-being?
How is animal well-being assessed?
How does one interpret and use existing information?

At the time of this writing, there are many more questions than answers.

Biomedical and behavioral scientists must strive to develop an acceptable definition and understanding of animal well-being and to implement objective and valid means of evaluating well-being of laboratory animals. From the physical well-being perspective, this has been at least partially accomplished. Much emphasis has been placed on physical factors such as freedom from disease and contamination. This has led to strict veterinary care and disease control practices, cleaning and sanitation protocols, guidelines for facility construction, and other management practices and programs focused on the standardization of animal care and use and the reduction of variables to improve the quality of science. Until recently, however, there has been little interest in psychological well-being of animals unless specific activities or data interpretation were overtly affected.

Animal well-being represents a close interrelation between animals' physical and mental states, involving much more than humane care. To consider each animal's quality of life, it is necessary to evaluate many other factors such as its needs, perspectives, and feelings as well as the values of the human society in which the animals exist. To determine the physical and mental states of animals, we must evaluate different viewpoints and consider using a variety of criteria and measures.

A reductionist view of well-being (that is, one of single cause and effect) separates physical and psychological/mental aspects of well-being. The reductionist attempts to isolate disciplines and to study areas with individual factors and respective roles in animal well-being. In a holistic view of well-being, however, proponents point to increasing evidence that physical and psychological phenomena are not distinct or separate. Instead, they view molecules, cells, organs, systems, the animal, the social group, and the entire environment as stimuli, responses, and interacting variables. The holistic vocabulary incorporates terms such as biopsychosocial, mind-body, and physical-psychosocial-mental-psychological.

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 physiological, biochemical, and behavioral characteristics change when an animal is exposed to aversive situations and stimuli, although many also change with the onset of routine life events and positive general arousal such as play, pleasant experiences, and sexual excitement. To compile a complete mental and biological profile of animals, one must evaluate numerous criteria such as performance, clinical state, neurochemistry, endocrinology, immunology, morphology, behavior, ethology, and preference. The different systems, processes, and individual specific responses interrelate and interact in a well-structured manner.

Relatively few empirical studies have addressed psychological well-being in animals, and little objective information exists on this subject. However, extensive literature has accumulated in related fields such as basic animal biology, animal behavior, farm animal science, stress biology, and psychoneuroimmunology. Even though animal well-being, per se, has not been a primary goal of many of these studies, much of this information is likely to be useful in developing a better understanding of animal well-being.

This issue of ILAR Journal is intended to stimulate increased dialogue and understanding among diverse groups that can contribute to this complex, evolving area. The 5 articles in the issue representing the respective authors' diverse scientific disciplines discuss research data that can contribute to our understanding of various aspects of animal well-being.

Morphology and pathology are integral aspects of evaluating animal well-being. We have known for many years that threats to homeostasis over the long term can lead to gross and microscopic changes in the anatomy of organs. It is generally accepted that intense aversive stimuli strongly enhance the occurrence of organ damage such as cardiovascular diseases and gastric ulcers in animals and humans. For example, prolonged release of free fatty acids into the blood stream by several hormones may result in the formation of fatty deposits in blood vessel walls and may therefore contribute to atherosclerosis. Prolonged hypertension in response to aversive stimuli may be associated with the formation of arteriosclerotic changes in the kidneys. A variety of aversive psychosocial stimuli are known to cause peptic ulcers in animals. Additional examples of pathology associated with aversive stimuli include amyloidosis, adrenal hypertrophy and hemorrhage, changes in skeletal muscle, acceleration of normal age-related changes of the retina, and weight changes in certain organs. For instance, immune suppression induced by aversive stimuli often leads to smaller spleens and thymus glands.

Ms. Benefiel's and Dr. Greenough's paper reviews a specific aspect of morphological change related to environmental enrichment. Compared with animals in a less enriched environment, the laboratory rats they studied had a heavier and thicker visual cortex, more extensive dendritic branching of neurons, and more synapses per neuron in the brain. The authors address sensitivity of the developing nervous system to experience and lifelong information storage.

There is considerable evidence that aversive physical or psychological stimuli can affect the health of humans and animals, that the mental state of an individual may determine the activity of body defenses, and that the nervous system can modulate immune responses. Dr. Capitanio's paper reviews the relationship of social experience and immune function and their relation to well-being. Specifically, he supports a holistic view and the use of immune function as indications of well-being; and he addresses the implications of environmental factors in management and research decisions.

Animal behavior, which can be observed directly and noninvasively, is very useful in the assessment of animal well-being. Dr. Mench's paper addresses the development of behavioral approaches to the study of animal well-being, the reasons behaviors are important, and the use of behavior in designing animal housing and environments.

In 1975, Drs. Ader and Cohen (1975) demonstrated that immune responses can be learned or classically conditioned, thus providing convincing empirical support for the concept of nervous system-immune system interactions. Dr. Ader's reprinted review in this issue shows that the nervous, endocrine, and immune systems influence one another through an elaborate system of chemical messengers that includes neu-rotransmitters, hormones, and cytokines, and that interactions among these 3 systems may have important implications for various forms of physical and psychological pathology in both human and animals.

The paper by Fullwood and others acknowledges the relatively few empirical studies that have addressed the caging needs of laboratory animals and points out the need for such studies on which to base recommendations. Determining appropriate housing conditions for animals is a complex matter involving interaction of many environmental factors and internal responses. Using several diverse assessment criteria, this paper addresses these issues for mice in a specific situation.

Interest in and concern about animal well-being have increased recently due to changing views toward nonhuman animals, societal attitudes, legislation, and conduct of quality scientific research and testing. Because animal well-being is multidimensional but not scientifically or technically precise, we recognize limitations in determining the overall well-being of an animal and comparing well-being in disparate environments. Continued research and discussion are needed to improve our knowledge about this critically important area. The following papers represent the work of several scientists whose goal was not necessarily to study animal well-being, yet whose results are useful in understanding the need for continued study.

REFERENCE

Ader R, Cohen N. 1975. Behaviorally conditioned immunosuppression. Psychosom Med 37:333-340.