Investigating the use of dietary magnesium on pig performance, welfare and stress during key life events

Some processes and practices commonly used in pig production may be experienced by the animals as stressful, negatively impacting pig performance and welfare, as well as farm productivity and profit. Research in rodents and humans has demonstrated that dietary magnesium is effective at reducing stress. However, research in other species is limited. This thesis investigated the impact of dietary magnesium supplementation on stress, performance, and welfare during key life events in farmed pigs. A systematic review indicated that magnesium supplementation can positively impact welfare, stress, and behaviour, although the literature was limited. A survey of farmers reflected this finding, but highlighted gaps between scientific research and commercial application in the timing of supplementation. To examine the effect of supplementary magnesium phosphate, with or without phytase, on physiological and behavioural measures of stress during regrouping, a study was conducted with 240 pigs over five weeks. In a separate study, two types (phosphate and sulphate) and levels (0.2% and 0.3%) of magnesium were supplemented in the diet of 240 pigs pre- and post-weaning. Magnesium phosphate improved performance and reduced body lesions scores post- weaning, but not in grower pigs. However, magnesium phosphate positively impacted pig behaviour in grower pigs despite no difference in cortisol measures. Despite an increase in dietary magnesium level, there were no further benefits of supplementing magnesium phosphate with phytase. Post-weaning, magnesium sulphate resulted in poorer performance and faecal scores. Taken together, the results of these novel studies demonstrate that dietary magnesium phosphate may improve or maintain performance post-weaning, and can improve pig behaviour and welfare during stressful events. The effects of magnesium phosphate on the stress response during these events, and potential interactive effects with other nutrients, needs further exploration. This thesis elucidates the benefits and advances understanding of the impact of magnesium supplementation on pig welfare, stress, and performance.