Nutritional influences on gut physiology and microflora in the post-weaned piglet
In piglets, the post-weaning growth check is commonly associated with the weaning process that occurs within the European Union at approximately 3-4 weeks of age. The aims of the studies reported here were to investigate the contribution and importance of nutritional influences on the complex and multi-factorial problem of the post-weaning growth check in the piglet. Multi-disciplinary investigations focussed upon the relationship between post-weaning nutrition and the gut ecosystem with specific emphasis on gut physiology, immunity and microflora. The influence of dietary acid binding-capacity (ABC) on gut morphology characteristics was investigated in 20 newly-weaned piglets up to 14 days post-weaning. Piglets offered the low ABC diet displayed more rapid recovery of villus height (after a degree of villus atrophy) than control animals (P<0.001). Prior to the initial villus atrophy, villus height increased significantly throughout the experimental period for both dietary treatment groups (P<0.001; <0.001 (L); <0.001 (Q)). In control animals, villus width was greater (P=0.006) compared with treatment animals, and villus width increased over time for both groups (P<0.001; <0.001 (L); 0.014 (Q)). Crypt depth also increased temporally (P<0.001; <0.001 (L)) for both dietary groups, with treatment animals exhibiting the greatest overall dietary mean (P=0.009). No significant differences between ileal digesta pH and feed intake levels were determined. Despite the improvements in intestinal structure post-weaning, these effects were not manifested in increased performance, i.e. DLWG. The improvements in intestinal structure may not have been of significant magnitude to influence performance parameters. Dietary zinc oxide (ZnO) and avilamycin supplementation was found to exert a beneficial (although non-significant: P>0.05) effect on gut morphology; villus atrophy occurred over the initial 2 days post-weaning for animals fed ZnO, avilamycin or ZnO plus avilamycin (diets 2-4 respectively), compared to 4 days for control animals. No significant differences between intestinal coliform and lactobacilli load were established with respect to dietary treatment. Any differences observed in microflora load are most likely to be age-dependent. A positive relationship was established between dietary treatment (ZnO, avilamycin and ZnO plus avilamycin) on daily live weight gain post-weaning (P<0.001). Although not significant (P>0.05), a positive influence of dietary ZnO supplementation on feed intake levels was apparent, which may account, in part, for the enhanced growth performance. This finding was not however manifested through modifications of intestinal morphology or the lactobacilli and coliform populations studied. This further suggests that dietary ZnO may exert an effect either luminally or systemically. Further research is required to determine the mechanism responsible for the enhanced feed intake and DLWG response. The effects of feeding a yeast-based nucleotide source pre- and post-weaning revealed no significant differences with respect to villus height and width. Crypt depth was significantly greater in animals fed the treatment diet post-weaning (P<0.001). Post-weaning nucleotide-supplemented diets were found to significantly reduce intestinal coliform load (P=0.033). Such an effect was not evident in animals fed the diets pre-weaning, suggesting that the gut microflora may have adapted to the dietary regimen throughout the pre-weaning period. Lymphocyte blastogenesis assays revealed that piglets fed a yeast-based nucleotide source post-weaning might be immunosuppressed at the time weaning. Conversely, when the same diets (in terms of composition) were fed from 14 days pre-weaning (study 4), no indication of immunosuppression was evident. Since no dietary effects were apparent in either study, it is postulated that this could be a general effect of the diet per se and not the actual dietary composition. It is however also possible that the animals involved in study 4 were experiencing hypersensitivity reactions to the pre-weaning dietary antigens. These animals were also combating an E. coli infection. Additional studies are however required to identify conclusively a cause and effect relationship, and elucidate the complicated interactions between nutrition or feed intake and immunobiology in the post-weaned piglet. Implementation of dietary nucleotide-supplementation from 7 days pre-weaning through to 25 days post-weaning within a commercial environment was found to enhance significantly DLWG (P<0.001). In summary, the current work extends current knowledge and offers a greater understanding of the factors and complex process that influence the gut ecosystem and physiology in the post-weaned piglet. This thesis confirms the crucial role feed intake or, more specifically luminal nutrition, in post-weaned piglets and has highlighted key areas for future investigation.