The effects of environmental enrichment on the welfare of laboratory swine housed in isolation

摘要

Pigs are gaining popularity for use as models in many areas of biomedical research. However, little research has been done on the welfare of pigs within a laboratory setting. Housing conditions are generally designed for optimal control over the environment and there is possible need for environmental standardization necessary for accurate and valid results. Within research and laboratory settings, pigs are often housed in isolation and in barren environments. A common buffer for many of the stressors caused by isolation and barren housing is the implementation of environmental enrichment. Environmental enrichment involves the enhancement of an animal's physical or social environment and may be defined as an improvement in the biological functioning of captive animals resulting from modifications to their environment. For laboratory pigs, constraints mean that the enrichments should positively enhance the pig's biological functioning, yet be practical to employ within a laboratory setting.;For these reasons, our experimental enrichments focused on two items that we expected to be important for a pig housed individually in a laboratory type environment; namely companionship and comfort. In our first experiment (Chapter 2), knowing that pigs are highly social and that isolation is stressful, we offered the pigs access to sight and relative proximity to another pig. We also investigated whether provision of a mirror could mimic this. Secondly, also knowing that pigs in indoor housing systems spend the vast majority (75%+) of their time inactive, we offered the pigs access to a rubber mat that may offer a more comfortable lying surface than perforated metal flooring. In order to test the relative importance of these enrichments, we used a preference test in which the pigs could choose to spend time with only one resource. Our results showed that the preference of pigs is largely dependent upon their environment. Pigs showed an overall propensity to spend their time with the companion enrichment. Only when a human was present were the mirror and the companion enrichment equally preferred. Due to the strikingly different enrichment uses when an human is present compared to when a human is absent, our results confirm that preference studies are indeed sensitive to experimental conditions and using time as a cost associated with preference choice is not a reliable indicator of importance.;Additionally, there is a great need in laboratory animal welfare to refine the husbandry and use of laboratory animals and develop less invasive and validated methods for acquiring data and measuring stress. In our second study (Chapter 3) it was therefore our goal to 1) study the physiological and behavioral effects of isolation and environmental enrichment in swine housed within a novel system which allowed for automated blood sampling and 2) determine if tear secretion in pigs could be used as a non-invasive indicator of stress. We found the presence of enrichment had positive effects. Animals not isolated and not given enrichment had higher cortisol levels than those not isolated and given enrichment, possibly due to frustration in their inability to get to the conspecific. Numerous studies have shown that stress is often correlated with impairment of immune function. Our evidence that isolation may be having a negative effect on welfare was seen in a decrease in eosinophils. Furthermore, our investigation of tear staining as a non-invasive indictor of stress proved to be promising, with an increase seen with those animals housed in isolation.