The scientific assessment of the impact of housing on animal welfare: A critical review

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The issue of animal welfare, particularly in relation to legislation, involves philosophical, ethical, economic and political issues and is not just a matter for science. A scientific definition of welfare must address the concerns of the public, but is difficult to achieve because of a lack of consensus as to what good welfare involves. The assessment of animal welfare is best achieved using a mixture of design criteria (which specify what must be included in the environment) and performance criteria (which specify what the signs of good welfare are). The quality of stockmanship can have a major influence on animal welfare, and it should not be assumed that the method of housing is the major determinant of animal welfare. The validity of many of the proposed measures of welfare is difficult to determine because of a lack of understanding of the underlying biology. Measures of aversion are the best available measures of animal suffering caused by procedures of short duration, but whether they can be used to assess the effect of housing is uncertain. Consensus has not yet been reached on the issue of behavioral deprivation, but several measures of behavioral motivation can be used to determine if animals are frustrated, although none is free from criticism. Much abnormal, stereotyped behavior seems to reflect feeding rather than housing problems, and there is a lack of firm evidence that the level of stereotypic behavior correlates with the welfare of the animals. The method of housing can influence the animals' physiology, but this effect is not adequately described by measures of corticosteroids. Use of the term "stress" generates confusion. Production measures give some information about animal welfare but only if the causes of lowered production are known. Animal welfare is a complex phenomenon and one component of welfare should not be equated with the whole, nor should scientific assessment of welfare be considered a simple matter.