In 1994, Professor David Mellor and Dr Cam Reid proposed a new model as a means of systematically identifying and grading the severity of different forms of welfare compromise by reformulating the Five Freedoms as ‘Five Domains’ of nutrition, environment, health, behaviour and mental state  (Table 1).
Table 1 Five Freedoms and Five Domains – simplistic form
|Five Freedoms||Five Domains|
|1. From hunger and thirst||1. Nutrition|
|2. From discomfort||2. Environment|
|3. From pain, injury and disease||3. Health|
|4. To express normal behaviour||4. Behaviour|
|5. From fear and distress||5. Mental state|
This approach allowed a distinction to be made between the physical and functional factors that affect an animal’s welfare and the overall mental state of the animal arising from these factors. Over the past 20 years this paradigm has been widely adopted as a tool for assessing the welfare impacts of research procedures, pest animal control methods and other interventions in animals’ lives.
The Five Freedoms and Five Domains frameworks contain essentially the same five elements. However, the Five Domains explore the mental state of an animal in more detail and acknowledge that for every physical aspect that is affected, there may be an accompanying emotion or subjective experience that may also affect welfare. This is useful in terms of reinforcing the message that emotional needs are equally important as physical needs for animals.
One of the most important strengths of the Five Domains is the clarity it provides that merely minimising or resolving negative physical or mental states does not necessarily result in positive welfare, but may only provide, at best, a neutral state. To have good welfare, animals need more than this.
To help ensure animals have a ‘life worth living’ they must have the opportunity to have positive experiences, such as anticipation, satisfaction and satiation. To enable this, those responsible for the care of animals need to provide them with environments that not only allow, but encourage animals to express behaviours that are rewarding. This shift in understanding is the basis for the Five Domains model incorporating positive welfare states. You can read about this in detail here.
Thus, the Five Domains provide a means of evaluating the welfare of an individual or group of animals in a particular situation, with a strong focus on mental well-being and positive experiences. The Five Domains also allow us to extend our thinking beyond the Five Freedoms to place even greater emphasis on providing opportunities for animals to be exposed to or engage in activities which provide positive experiences.
 Mellor DJ (2017) Operational details of the Five Domains Models and its key applications to the assessment and management of animal welfare. Animals 7(8):60. doi:10.3390/ani7080060 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5575572/
 Mellor DJ & Beausoleil NJ (2015) Extending the ‘Five Domains’ model for animal welfare assessment to incorporate positive welfare states. Animal Welfare 24:241–253. doi: 10.7120/096272188.8.131.52.
 Mellor DJ & Reid CSW (1994) Concepts of animal well-being and predicting the impact of procedures on experimental animals. In Improving the Well-Being of Animals in the Research Environment; Australian and New Zealand Council for the Care of Animals in Research and Teaching (ANZCCART): Glen Osmond, SA, Australia, pp. 3–18.