A very popular approach to assessing animal welfare is to make a list of things that animals need. The general idea is that, if animals have the things on the list, then probably they’re happy.
The most popular list is the Five Freedoms, created by the Farm Animal Welfare Committee, which advises the British government about animal welfare. The Five Freedoms are:
1. Freedom from hunger and thirst by ready access to water and a diet to maintain health and vigor.
2. Freedom from discomfort by providing an appropriate environment.
3. Freedom from pain, injury, or disease by prevention or rapid diagnosis and treatment.
4. Freedom to express normal behavior by providing sufficient space, appropriate facilities, and appropriate company of the animal’s own kind.
5. Freedom from fear and distress by ensuring conditions and treatment which avoid mental suffering.
Sometimes you see the Five Domains; the difference between these two systems is impossible to understand for people who don’t have a PhD in animal welfare science.
But the Five Freedoms is far from the only list. Botreau et al (2009) say:
Good feeding
1. Absence of prolonged hunger.
2. Absence of prolonged thirst.Good housing
3. Comfort around resting.
4. Thermal comfort.
5. Ease of movement.Good health
6. Absence of injuries.
7. Absence of disease.
8. Absence of pain induced by management procedures.Appropriate behavior
9. Expression of social behavior.
10. Expression of other behaviors.
11. Good human-animal relationship.
12. Absence of general fear.
Fraser has a list of four criteria:
1. Maintain basic health (i.e. sufficient food, water, housing, and medical care)
2. Reduce pain and distress (i.e. preventing injuries and diseases which cause fear or pain)
3. Accommodate natural behaviors and affective states
4. Natural elements in the environment (i.e. outdoor access, sunlight).
Webster presents three questions:
1. Is the animal living in an environment consistent with that in which the species has evolved and to which the species is adapted? (Is the animal living a natural life?)
2. Is the animal able to obtain normal growth, function, and good health, and to sustain fitness in adult life? (Is the animal healthy?)
3. Is the animal experiencing a sense of mental satisfaction or, at least, freedom from mental distress? (Is the animal happy?)
These lists are pretty varied, but reading them over you can see some basic themes. I am tempted to make my own list summing up the other lists.
In general, all standards—those I listed and the ones I didn’t—agree that animals should be well-fed, physically comfortable, and in good health. They agree that animals should be able to do their ordinary behaviors, such as social behaviors and spending time outdoors. They also agree that animals should have a high level of subjective well-being, with as little fear and distress as possible.
This use of common-sense heuristics is perhaps the most common way that animal welfare is assessed in the field.