Various systems already exist to judge animal welfare - of which distress can be one component - in the laboratory setting (see Hendriksen and Morton 1998). Many rely on nonspecific measures; that is they may be manifestations of a number of states, not all of them necessarily indicative of poor welfare. Certainly, there is already good provision for methods to recognise some of the commoner manifestations of distress, arguably they are sufficiently meaningful to categorise various distress states, though to my mind they are for the present still not suited for use as means of strictly quantifying the negative impact/suffering on animal welfare that they represent. Generally they will allow the condition of individual animals to be described and assigned to broad categories, rather than allowing fine distinctions to be made. There is a need to continue to look carefully for means of properly discriminating distress and suffering produced by pain, from suffering and distress caused by other factors - as both the diagnosis of the cause and the provision of effective relief require a proper understanding of the cause of these negative states.
Richmond, Jon, "International Regulatory Definitions of Animal Distress in Animal Research and Animal Production – An Overview." (2009). LAW. 13.