Assessing animal welfare

Animal welfare is assessed by observing or measuring physical or behavioural features of the animal or qualities of the animal’s environment. These signs of animal welfare are known as ‘welfare indicators’. Welfare is complex, so it is usually important to assess more than one indicator to reveal the extent to which welfare is good or bad, rather than assessing just one aspect of the animal’s biology or environment.

There are three main sources of welfare indicators:

  1. The animal in its current situation, e.g. frequencies or durations of abnormal behaviour 1, concentrations of hormones 2, or body condition;
  2. The animal in a decision-making test, e.g. preference tests (reviewed in 3) and cognitive bias tests 4, 5; and
  3. The animal’s environment or situation, e.g. quality and quantity of the diet, presence of a hiding place, exposure to weather, or details of husbandry routines 6.

Furthermore, welfare indicators can be measured via a continuum between two main approaches:

  1. Objectively, e.g. quantifying rates, durations, frequencies, concentrations or intensities g. for behaviour: 7, 8; or
  2. Subjectively, g. owner/keeper questionnaires 9, qualitative behaviour assessment 10, or subjective lameness or pain scoring systems 11.

Which welfare indicators you should assess depends partly on whether your concept of welfare includes the animal’s feelings, physical functioning, and/or naturalness. Feelings can be crucial to some concepts of welfare, e.g. even healthy animals living in a naturalistic habitat could have poor welfare if they are anxious, bored, or socially stressed. Despite feelings being private to each individual, it is possible to measure the behavioural and physical signs of those underlying experiences 12-15.

The specific welfare indicators for any given scenario should be selected on the basis of:

  • the welfare concern or aim, e.g. preventing pain, or encouraging playfulness;
  • the timescale of interest, e.g. using vocalisations to assess fleeting experiences, or stomach ulceration to assess long term stress;
  • ethical considerations, e.g. assessing hormone concentrations non-invasively in faeces, rather than invasively in blood samples, where possible; and
  • feasibility, e.g. the amount of money, time, and skill required.

A hypothesis should be created with a specific prediction about whether each welfare indicator should increase or decrease under better (or poorer) welfare conditions. Other features of good scientific practice include ‘blinding’ the observer to sources of bias, random allocation of animals across treatments, ethical approval, repeatability, and appropriate sample sizes e.g. 7.

Good reviews of commonly used welfare indicators exist for different species or sectors of animal use, such as for zoo animals 16, 17. Well-chosen welfare indicators can provide evidence that allow reasoned conclusions to be drawn about animal welfare.


  1. Mason GJ, Rushen J. Stereotypic Animal Behaviour: Fundamentals and Applications to Welfare. Wallingford: CAB International; 2006.
  2. Palme R. Monitoring stress hormone metabolites as a useful, non-invasive tool for welfare assessment in farm animals. Animal Welfare. 2012;21:331-337.
  3. Kirkden RD, Pajor EA. Using preference, motivation and aversion tests to ask scientific questions about animals’ feelings. Applied Animal Behaviour Science. 2006;100:29-47.
  4. Harding EJ, Paul ES, Mendl M. Cognitive bias and affective state. Nature. 2004;427:312.
  5. Mendl M, Burman OHP, Parker RMA, Paul ES. Cognitive bias as an indicator of animal emotion and welfare: Emerging evidence and underlying mechanisms. Applied Animal Behaviour Science. 2009;118:161-181.
  6. Mellor DJ, Beausoleil NJ. Extending the ‘Five Domains’ model for animal welfare assessment to incorporate positive welfare states. Animal Welfare. 2015;24:241-253.
  7. Martin P, Bateson P. Measuring behaviour: an introductory guide. Cambridge: Cambridge University Press; 2007.
  8. Asher L, Collins LM, Ortiz-Pelaez A, Drewe JA, Nicol CJ, Pfeiffer DU. Recent advances in the analysis of behavioural organization and interpretation as indicators of animal welfare. Journal of The Royal Society Interface. 2009;6:1103-1119.
  9. Whitham JC, Wielebnowski N. Animal-based welfare monitoring: using keeper ratings as an assessment tool. Zoo Biology. 2009;28:545-560.
  10. Wemelsfelder F, Hunter TEA, Mendl MT, Lawrence AB. Assessing the ‘whole animal’: a free choice profiling approach. Animal Behaviour. 2001;62:209-220.
  11. Meagher RK. Observer ratings: Validity and value as a tool for animal welfare research. Applied Animal Behaviour Science. 2009;119:1-14.
  12. Dawkins MS. Using behaviour to assess animal welfare. Animal Welfare. 2004;13:S3-7.
  13. Duncan IJH. Science-based assessment of animal welfare: farm animals. Revue Scientifique et Technique – Office International des Epizooties. 2005;24:483-492.
  14. Mason GJ, Mendl M. Why is there no simple way of measuring animal welfare? Animal Welfare. 1993;2:301-319.
  15. Johnsen PF, Johannesson T, Sandoe P. Assessment of farm animal welfare at herd level: Many goals, many methods. Acta Agriculturae Scandinavica Section a – Animal Science. 2001;S30:26-33.
  16. Mason GJ, Veasey JS. How should the psychological well-being of zoo elephants be objectively investigated? Zoo Biology. 2010;29:237-255.
  17. Wolfensohn S, Shotton J, Bowley H, Davies S, Thompson S, Justice WSM. Assessment of Welfare in Zoo Animals: Towards Optimum Quality of Life. Animals. 2018;8.

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