The quality of animal life includes different elements of life – health, satisfaction and longevity. Science has taken up welfare as a subject of scientific research and, above all, it gives the answer to the question of what the animals perceive as quality life.
Because of ideological, religious, economic, and sociological approaches, the various elements of life are considered to have different degrees of importance, so three basic concepts and approaches to the exploration of welfare have been developed worldwide.
The first concept links animal welfare to their natural environment. Animals are supposed to live in an environment that allows them a natural behaviour. The main starting point for the assessment of welfare is the expression of species-specific behaviour. The second concept of welfare links it with the biological functioning of animals. Here the central issue is the animal's ability to adapt to different environments. Animal welfare is therefore expressed as the degree of successful adaptation to its immediate current environment. In this regard, the genotype of animals is also important. The main methodological approach within this concept is to assess welfare by applying criteria that indicate the difficulties of a specimen in controlling its environment. The set of welfare indicators includes, in particular, the assessment of animal health condition, of injuries, of growth, development and reproduction disorders, as well as quantitative measurements of physiological values and of behaviour. The third concept relates to the subjective feelings of animals. Caution is needed in this concept, since it can only be reasonably applied as appropriate for sentient animals, and it defines welfare as a subjective experience of animals, which is extremely difficult to measure objectively. A more widely used research approach includes studies of animal preference for different environments and the degree of animal motivation to acquire or avoid a particular element in the surrounding area.
In the early 1970s, research topics focused on measuring the negative aspects of life – suffering, pain, fear – while over the last fifty years, the focus of welfare research has also shifted towards positive aspects of life (assessments and measurements of happiness, playfulness, satisfaction).