BackgroundAnimals captive bred for reintroduction are often housed under conditions which are not representative of their preferred social structure for at least part of the reintroduction process. Specifically, this is most likely to occur during the final stages of the release programme, whilst being housed during transportation to the release site. The degree of social stress experienced by individuals during this time may negatively impact upon their immunocompetence.Methodology/Principal FindingsWe examined two measure of stress - body weight and Leukocyte Coping Capacity (LCC) - to investigate the effects of group size upon captive-bred water voles destined for release within a reintroduction program. Water voles were housed in laboratory cages containing between one and eight individuals. LCC scores were negatively correlated with group size, suggesting that individuals in larger groups experienced a larger degree of immuno-suppression than did individuals housed in smaller groups or individually. During the course of the study mean body weights increased, in contrast to expectations from a previous study. This was attributed to the individuals sampled being sub-adults and thus growing in length and weight during the course of the investigation.Conclusions/SignificanceThe reintroduction process will inevitably cause some stress to the release cohort. However, for water voles we conclude that the stress experienced may be reduced by decreasing group size within captive colony and/or transportation housing practises. These findings are of significance to other species' reintroductions, in highlighting the need to consider life-history strategies when choosing housing systems for animals being maintained in captivity prior to release to the wild. A reduction in stress experienced at the pre-release stage may improve immunocompetence and thus animal welfare and initial survival post-release.

In the wild, European badgers, Meles meles, naturally display marked individual and seasonal variation in body condition. To establish whether body condition affects their ability to produce an antioxidant defence when exposed to immunological stress, we tested the plasma antioxidant capacity of eighty-eight wild badgers using analysis of emitted light antioxidant kits, with values expressed as vitamin E analogue (VEA) equivalents. The body condition of subject animals was a key explanatory variable in the extent of the antioxidant responses observed. Naturally emaciated animals in the poorest body condition mounted a significantly lower antioxidant response than that recorded for animals with more body fat. Related to natural cycles in body fat (reflecting feeding success), a significant seasonal effect was also observed, VEA equivalent values being significantly higher in autumn than in summer. In addition, animals were also assigned to one of two experimental regimes: non-transported (n= 18), that is, sampling at the site of capture, or sampling immediately after transport (transported n = 70). Transport consisted of a ride for o10 min (around 1500 m on average) while caged, on a trailer pulled by an all-terrain quad bike; this was a necessary part of our wider studies of these badgers, but incidentally also providing a standardized stressor. Transportation had a marginal, but non-significant, effect on antioxidant capacity, and sex had no interactive effect on the outcome of the transportation treatment, or on body-condition results. These findings are discussed in the context of seasonal corollaries with foraging ecology, giving particular consideration to changing climatic conditions and species management.

Wild badgers (Meles meles) in Wytham woods, Oxfordshire, are routinely trapped, transported to a central field laboratory, studied and released as part of an on-going population study. These procedures have been carefully developed to minimise impact on the badgers' welfare; however they are potentially stressful, and, as part of our on-going welfare refinements, and our exploration to develop methods for quantifying stress in wild mammals, we studied the effects of transport stress on neutrophil activation in wild trapped badgers. Blood samples were obtained from 28 badgers. We compared three transport regimes: transported (n = 9), transported and rested for at least 30 mins (n = 11), and not transported (n = 8). Total and differential white cell counts were carried out and neutrophil activation was measured by the nitroblue tetrazolium test. Our goal was primarily to validate neutrophil activity as an indicator of stress, on the basis that the transport treatment was expected to be more stressful than the non-transport treatment. There were significant increases in % activated circulating neutrophils in response to transport. This study supports the proposition that stress affects circulating neutrophil numbers and the state of their activation, as determined by the nitroblue tetrazolium reduction assay, and therefore adds weight to the idea that neutrophil activation is a potential measure of stress in wild animals.