Many definitions of "animal welfare" have been proposed. According to the American College of Animal Welfare, "animal welfare" refers to “the state of the animal.” Some definitions incorporate the different aspects of animal welfare. For example, David Fraser proposed that the welfare of an animal is determined by three key components: 1) the animal's physiology, 2) its ability to perform species-typical behavior, and 3) its emotional state (1). "Good welfare" exists when all three components are at satisfactory levels, and welfare is assessed on a continuum from poor to adequate to good. A 2025 article provides a good overview of how this three-pronged approach to animal welfare applies to the veterinary profession (2).
The original framework for animal welfare science was that of the “Five Freedoms": freedom from hunger or thirst; freedom from discomfort; freedom from pain, injury, or disease; freedom to express normal behavior; and freedom from fear and distress (3). The current framework, the "Five Domains," is more specific and direct in addressing animal welfare. The Five Domains of animal welfare are as follows (4):
nutrition
environment
health
behavior
the resulting mental state
The Five Domains model encourages veterinarians to think beyond providing freedom from negative experiences and focus more on providing positive experiences.
Determining the welfare of an animal (or population of animals) is fundamentally an effort to view the world from the animal’s perspective. A veterinarian making a welfare assessment should attempt to discern whether the animal has an acceptable balance of negative and positive experiences and is able to cope within its environment to obtain its needs.
Although animal welfare and ethics are intertwined, it is important to be able to distinguish between the ethical questions and the factual data that inform animal welfare assessments. Ethical questions illuminate areas of societal concern, whereas animal welfare science elucidates an animal's biological processes and responses to its environment. For example, whether humans should be allowed to use animals in biomedical research is an ethical question; how a laboratory animal responds to the conditions it is experiencing is a matter of animal welfare science.
Veterinarians play a variety of integral roles in improving the welfare of animals, from helping an individual animal during a clinical appointment to working with populations of animals in research laboratories, livestock farms, and animal shelters.
Laws and Regulations Concerning Animal Welfare
Laws and regulations related to animal welfare are enacted by either federal, state, or local municipalities. Examples in the US at the federal level include the Animal Welfare Act, the Fur Seal Act, and the Twenty-Eight Hour Law. State and local laws can be more restrictive than federal laws, and examples include those regarding animal cruelty, breed-specific legislation, and specific housing requirements.
There are numerous international entities that promote animal welfare by providing a framework for international cooperation. The World Organisation for Animal Healthprovides international standards for animal welfare, including standards for shipping, production systems, and slaughter.
Assessment of Animal Welfare
Measurement of Physiology, Behavior, and Emotions for Animal Welfare Assessment
No single measurement can quantify the state of an animal’s welfare. Animal welfare assessments are multifaceted and include physiological and behavioral measures, as well as assessments of emotional state. Furthermore, some measurements are animal-based, and others are facility-based. Animal-based measures assess how an animal is responding to its environment. Facility-based measures assess the environment itself. For example, an assessment of scratches or other skin lesions is an animal-based measure; measuring the size of the animal's pen is facility-based.
Physiological measures of welfare include those that reflect the overall health of animals, such as mortality rates and lifespan, as well as measurements of productivity (eg, milk production, reproduction rate) and disease incidence. Often, hypothalamic-pituitary axis measurements are used to determine stress responses in animals; for a particular animal, concentration of the species-relevant glucocorticoid might be measured(5). Although physiological measures are a key part of welfare assessment, they often lack valence (intrinsic, measurable value); for example, an animal's glucocorticoid concentration might increase after a painful procedure or after a positive social interaction. For this reason, behavioral and emotional responses must also be evaluated for a well-rounded welfare assessment.
Behavioral measurements of welfare indicate how well an animal functions or how frequently an animal demonstrates a particular behavior. Behavioral indicators of good welfare include the following:
normal exploratory behavior
alertness
normal interaction with others
normal play behaviors
Behavioral indicators of poor welfare include the following:
stereotypic behaviors
abnormal fear behaviors
excessive aggression
behaviors directed toward an atypical object
behaviors related to pain or illness
The frequency, duration, and intensity of the behaviors, and the number of animals in a population demonstrating the behaviors, provide a quantitative measure of the welfare of an individual or population.
Measures of emotion in animals have often been considered controversial; however, progress continues to be made in this area. One method of assessing emotional states in animals is called cognitive (or judgment) bias (6). In this method, an animal is trained to a positive cue and a negative cue and then given an ambiguous cue. If the animal approaches the ambiguous cue, it is said to be in a positive affective state; if the animal treats the ambiguous cue as negative, it is said to be in a negative affective state. This approach has been used to assess how animals respond to different situations, such as a painful procedure with and without analgesia, and has been tried in many species, from honeybees to pigs (7).
An emerging trend in animal welfare science is the focus on assessing positive states in animals ("positive welfare"), rather than just preventing negative states. A state of positive welfare is one in which the animal is able to engage in rewarding, goal-directed behaviors, such as affiliative behavior between a mother and offspring. Other behaviors, such as play, are considered indicators of positive welfare.
Good welfare is a balance of physiological, behavioral, and emotional factors. Sometimes, improvement in one welfare measurement correlates to a decline in another aspect of welfare.
Standardized Animal Welfare Assessments
The goals of an animal welfare assessment are usually developed and standardized by experts in a specific animal population, whether production animals, sheltered dogs and cats, or laboratory animals. Standardized assessments should identify the indicators used in evaluation, including animal-based indicators (eg, lameness or body condition scores) and production-based indicators (eg, milk production). The measures should be valid and reliable, and the protocols should be reproducible.
Standardized welfare assessments can be used in welfare certification and auditing programs, as outlined by the USDA. They are also incorporated into institutional and regulatory oversight protocols, such as those established by Institutional Animal Care and Use Committees (IACUCs) for animals in research settings.
For More Information
Also see pet owner content regarding welfare of pets.
References
Fraser D, Weary DM, Pajor EA, Milligan BN. A scientific conception of animal welfare that reflects ethical concerns. Anim Welf. 1997;6(3):187-205. doi:10.1017/S0962728600019795
Beaver BV, Meunier L, Peralta JM, et al. What is animal welfare and why does it matter to veterinarians?Today's Veterinary Practice. March-April 2025. Published online February 17, 2025.
Brambell FWR. Report of the Technical Committee to Enquire Into the Welfare of Animals Kept Under Intensive Livestock Husbandry Systems. Her Majesty's Stationery Office; 1965.
Mellor DJ. Updating animal welfare thinking: moving beyond the “Five Freedoms” towards “a life worth living”. Animals (Basel). 2016;6(3):21. doi:10.3390/ani6030021
Moberg GP. Biological response to stress: implications for animal welfare. In: Moberg GP, Mench JA, eds. The Biology of Animal Stress: Basic Principles and Implications for Animal Welfare. CABI; 2000:1-22.
Mirza U. Animal memory. In: Rana T, ed. Principles of Animal Behavior: Aspects of Behavioural Biology and Evolution. CRC Press; 2025:45-55.
Mendl M, Burman OHP, Parker RMA, Paul ES. Cognitive bias as an indicator of animal emotion and welfare: emerging evidence and underlying mechanisms. Appl Anim Behav Sci. 2009;118(3-4):161-181. doi:10.1016/j.applanim.2009.02.023
