Howarth, GordonWhittaker, AlexandraBarker, Timothy Hugh2019-03-172019-03-172018http://hdl.handle.net/2440/118200The identification of cognitive biases has become an important measure of animal affective (emotional) state, and therefore, animal welfare. Negative cognitive biases can be evidenced by animals preferentially processing novel information pessimistically and judgement-bias testing is the commonplace methodology to detect such biases. As the use of judgement-biases has increased in the scientific community, concerns regarding the efficacy and repeatability of these methods has been questioned. This body of work began with the aim of identifying the effects that a common housing procedure would have on judgement bias expression in rats. However, after analysis of data multiple confounding factors were identified that were argued to have seriously impacted on validity of methods employed. Therefore, investigations in this thesis focussed on a commonly employed, active choice judgement bias test as used in rats. Confounding factors that have received limited attention in the literature have been applied to these studies. These factors include phase of oestrous, social status, housing density and space allocation. It was aimed to investigate if the judgement bias test employed can find practical utility in welfare assessment of the laboratory rat. In addition to investigating the effects of external factors on animal expression to the judgement bias test, investigations into the mechanistic nature of the test were also undertaken. Extinction of learning, which results in the animals failing to perform the test parameters, is a commonly reported limitation of these methods, as are significantly long training times often associated with their use. These two factors were also identified and studied in this thesis, with the aim of improving practicality of the judgement bias discrimination task (JBT) to allow its employment in applied animal husbandry situations. This thesis has identified many potentially confounding concerns of judgement bias testing in rats. Whilst evidence suggests that the JBT may never find practical use as a welfare assessment technique, it remains an extremely important indicator of animal affect. Improved understanding of these confounding factors will increase validity of the JBT as a tool for detection of affective state.enThesis