Dietary strategies to minimize the detrimental impact of weaning on gut morphology, physiology and microbiota of piglets

Weaning is a crucial period in the management of piglets. In modern piggeries economic interest make weaning age decrease more and more and the detrimental consequences of weaning have as much importance as earlier the weaning occurs. The risk of development of post-weaning diarrhea (PWD) in piglets is high and PWD is the cause of serious economic losses in pig herds. In the past the supplementation of the feed given after weaning with growth promoters antibiotics, in order to keep PWD under control, used to be a common practice, but their usage has been banned in EU since 2006. This measure led to the investigation of alternative suitable feed supplements that would be reasonably efficient in protecting and sustaining animal health and performance. Aim of this thesis was to evaluate the effect of some different alternatives to growth-promoters antibiotics on weaning piglets and to assess if some of them could be considered as valuables options to replace auxinic in animal feeding. The study is composed by four experimental trials. The first one aims to identify mechanisms involved in the auxinic effects of antibiotics in the diets; the following three evaluate the addition butyric acid, tryptophan, and nitrate as alternative to in-feed antimicrobials. Although some results are controversial, it appears from the data presented that the alternatives to in-feed antibiotics considered may exert positive effects on some zootechnical and health parameters on piglet in the post-weaning period. Anyway, the mechanism of action and the interaction with microbiota of such additives should be investigated inside out because many effects remains poorly understood.

Diet Effects on Activation and Maturation of Feed Control over the Gastrointestinal Defence Barrier in Piglets

Weaning is an important and complex step involving many stresses that interfere deeply with feed intake, gastro-intestinal tract (GIT) development and adaptation to the weaning diet in young pigs. The health of the pig at weaning, its nutrition in the immediate post-weaning period, and the physical, microbiological and psychological environment are all factors that interact to determine food intake and subsequent growth. GIT disorders, infections and diarrhoea increase at the time of weaning, in fact pathogens such as enterotoxigenic Escherichia coli (ETEC) are major causes of mucosal damage in post-weaning disease contributing to diarrhoea in suckling and post-weaned pigs. The European ban in 2006 put on antibiotic growth promoters (AGP) has stimulated research on the mechanisms of GIT disorders and on nutritional approaches for preventing or reducing such disturbances avoiding AGPs. Concerning these aspects here are presented five studies based on the interplay among nutrition, genomic, immunity and physiology with the aim to clarify some of these problematic issues around weaning period in piglets. The first three evaluate the effects of diets threonine or tryptophan enriched on gut defence and health as possible alternatives to AGP in the gut. The fourth is focused on the possible immunological function related with the development of the stomach. The fifth is a pilot study on the gastric sensing and orexygenic signal given by fasting or re-feeding conditions. Although some results are controversial, it appears that both tryptophan and threonine supplementation in weaning diets have a preventive role in E.coli PWD and favorable effects in the gut especially in relation to ETEC susceptible genotype. While the stomach is believed as almost aseptic organ, it shows an immune activity related with the mucosal maturation. Moreover it shows an orexygenic role of both oxyntic mucosa and pyloric mucosa, and its possible relation with nutrient sensing stimuli.

Feeding the Gut Microbiome and Immune Maturation to Manage Weaned Piglets

This thesis reports five studies that may contribute to understand how weaning affects the immune and intestinal microbiota maturation of the piglet and proposes some possible nutritional strategies to attenuate its negative effects. The first study showed that weaning is associated in Payer’s patches with the activation of MHC response against class I antigens and that related to the stimulation to IFN-γ and showed, for the first time, that their blood at weaning remains dominated by immature blood cells. In the second study we tested if the use of a live vaccine against a conditionally but also genetically based intestinal disease, like PWD, could have an impact on the growth performance of pigs and their intestinal microbiota and if it could provide a model to test the response to nutritional strategies under conditions of an immune and intestinal stimulation for animals susceptible to ETEC type. In this study, we demonstrated how a vaccinal strain of F4/F18 E. coli can affect the gut microbial composition of piglets, regardless of their genetic susceptibility to ETEC infection. In the third study we evidenced how a nucleotide supplementation can favor the proliferation of jejunal Peyer patches and anticipate the maturation of the fecal microbiota. In the fourth study we reported how xylanase can favor the proliferation of Lactobacillus reuteri. Finally, we showed some first results on the muscles fiber development in fast- and slow-growing suckling pigs and the relationship with the intestinal microbiota. Taken together, the results presented in this thesis provide new insight about the interplay between the host-genetics, gut microbial composition, and host physiological status. Furthermore, it provides confirmation that the use of known genetic markers for ETEC F4 and F18 could represent a potential tool to stratify the animals in the trials both in healthy or challenge-based protocols.