Animal welfare in livestock production comes in different levels, as determined by the cost, benefit and ethics of each situation.
The cost refers to the expenditure in the way of providing higher welfare compared to lower welfare. For example, a larger roaming space for chickens would incur a cost of fewer eggs laid in total from fewer chickens in the same area that could be occupied by more chickens with less space.
The benefit refers to positive outcomes coming from higher welfare compared with lower welfare. For example, stressful conditions could impact negatively on animal development and the quality of subsequent products derived from them, so providing a higher level of welfare incurs a benefit to the final product.
Ethics refers to the acceptable level of welfare of animals regardless of the cost-benefit analysis. Ethics is about what is acceptable at any cost. Ethics is about what is unacceptable at any benefit. For example, is there a level of animal welfare that is too low to be acceptable under any circumstances, including those where the benefit is otherwise high?
Assessing animal welfare involves observing behavioural indicators. As such, this is part of the field that studies animal behaviour more generally, called ethology.
Categories of animal behaviour indicating distress include stereotypy, misdirected behaviour, failure in sexual and parental behaviour and altered levels of activity.
Stereotypy is the repetitive behaviour seen with no obvious cause, as seen with certain movements, utterances or postures. It can occur to provide some sensory stimulation to the animal, or as a replacement for adequate physical activity when isolated in confined spaces.
Misdirected behaviour is normal behaviour aimed in the wrong direction. For example, chicken over-plucking or trying to chew on inanimate objects are misdirected behaviours.
Lower reproductive success is also a symptom of poor welfare.
Studies to accumulate data on the ethology of domesticated animals in their natural or semi-natural environment take place in order to inform better practices. This helps maximise animal welfare in domesticate settings.
Additionally, preference tests can elucidate further the welfare state of an animal. They involve introducing an animal to a response mechanism that connects a signal, such as ringing a bell, to an outcome that they may or may not be interested in. By comparing e.g. a food reward with a social contact reward, we can establish the motivation of the animal towards certain things.