The gradual weaning of piglets: The influence of intermittent suckling and co-mingling on performance, the stress response, behaviour, and function and morphology of the gastrointestinal tract

A series of 5 experiments was conducted to test the general hypothesis that piglets subjected to intermittent suckling (IS, where piglets are temporarily separated from the sow during lactation) would have improved performance and gastrointestinal tract (GIT) structure and function after weaning compared with piglets weaned via conventional methods (abrupt weaning). It was also hypothesised that IS would not induce any additional stress or compromise piglet welfare before and after weaning, and that IS may in fact reduce the stress response immediately after weaning due to increased familiarity with creep feed and maternal separation. Piglets born to primiparous sows were the main focus of this thesis since they are lighter at birth, more susceptible to disease and generally have poorer performance than sow progeny, making them the most disadvantaged group at weaning. Separation times of 8 hours per day or 16 hours overnight were chosen for the IS regimen. Sugar absorption tests involving oral doses of mannitol, galactose and lactulose before and after weaning were used as markers of GIT tract absorptive capacity and permeability, and the stress response was assessed using a combination of neuroendocrine, immune, inflammatory and behavioural measures. Apart from a transient peak in cortisol and reduction in growth at the start of IS, the IS procedure was not associated with a chronic stress response. Onset of IS at an older age with an extended lactation (5 weeks instead of 4 weeks) markedly improved creep feed intake, post-weaning performance and galactose absorption in piglets born to primiparous sows. However, starting IS at 3 weeks with weaning at 4 weeks increased creep feed intake and post-weaning performance when progeny from multiparous sows were used and gave a varied response for primiparous sow progeny. Furthermore, IS in piglets born to primiparous sows had no effect on GIT permeability and did not attenuate post-weaning GIT structural changes, but rather advanced them as lactation progressed with IS piglets showing reduced absorption of mannitol and galactose before weaning. Longer separation times (16 hours versus 8 hours) had no impact on post-weaning performance or the stress responses, but did induce a more severe growth check at the start of IS. To further attenuate the stress associated with weaning, co-mingling (CoM, preweaning socialisation of piglets from different litters) was explored. It was hypothesised that CoM would improve post-weaning performance and GIT function through the facilitation of social eating behaviour and reduced aggression, and that combining IS with CoM would improve these measures additively. While CoM did not affect performance before or after weaning, post-weaning aggression was reduced and CoM piglets had the smallest changes in mannitol absorption over the periweaning period indicative of a larger GIT surface area. The combination of IS with CoM in piglets from multiparous sows additively improved post-weaning performance in the first week after weaning, but only when familiar groups remained together. From the experiments conducted in this thesis, it was shown that IS can improve piglet adaptation to weaning in multiparous litters, however IS in piglets born to primiparous sows gave varied responses. Furthermore, better performance outcomes were achieved if piglets had the opportunity to socialise with non-littermates and remain in familiar groups after weaning. It was shown that oral dosing with various sugars could be used in vivo to assess post-weaning changes to the GIT