Fibre in the diet of the suckling pig : opportunities for the maturation of the gastrointestinal tract and post-weaning resilience

Research with weaned piglets has provided information that dietary fibre (DF) is implicated in gastrointestinal (GIT) maturation and health. Dietary fibre can mitigate the risk for intestinal infections and diarrhoea occurring in pigs that are weaned at 3 to 4 weeks of age, which is common practice on most farms. There is a paucity of scientific information, however, on the role of DF in the diet of suckling pigs. A pig is born with a relatively immature gastrointestinal tract able to digest and absorb nutrients from sow milk. To attain capacity to digest diets containing high levels of vegetable feedstuffs the GIT needs to go through a process of maturation. In a natural setting, a large part of a pigU+2019s diet consists of vegetable fibrous feedstuffs, such as leaves, roots, tubers, fruits, and seeds. Wild boar and feral piglets are anticipated to start consuming non-milk feed items already early in life, including vegetable material. This allows gradual adaptation of the GIT and its harbouring intestinal microbiota to the solid diet before weaning, which is completed in nature at 10-17 weeks of age. The diet of farmed pigs also contains a high proportion of vegetable material, with varying levels of DF. Commercial pre-weaning diets , on the other hand, are formulated to be highly digestible and nutrient-dense, using sow milk as the benchmark. In this regard, there seems to be a major difference in diet characteristics between the natural diet and a typical commercial low-fibre, nutrient dense piglet diet. The implications of this difference for the maturation of the GIT are not known. Chapter 1 provides a literature overview of the significant maturational changes in dentition and the GIT after birth. For this thesis, it was decided to focus on the stomach, small and large intestine, as these organs play a central role in feed digestion and absorption. The available information shows that early nutrition of piglets modulates many aspects of the maturational processes of the GIT and the residential microbiota. The microbiota, mostly bacteria, are starting to colonize the GIT of the piglet from the immediate prenatal period onwards, especially in the large intestine where they are most abundant. Its composition develops with age of the pig in a complex coexistence with the host and the diet. The microbiota thrive on undigested nutrients, sloughed off intestinal cells and secretions (e.g., mucus, enzymes) through a process called fermentation. From the fermentation of carbohydrates, mostly volatile fatty acids are produced, such as acetate, propionate and butyrate. Volatile fatty acids are an energy source for the intestinal mucosa and the host. Furthermore, they play a role in many body processes, such as immune modulation, mineral and water absorption in the hind gut among many others. The end- products from protein fermentation, such as ammonia and branched-chain fatty acids and biogenic amines are mostly regarded as a risk for intestinal health. It is generally accepted that the intestinal microbiota play a pivotal role in GIT maturation and general health of animals, but the underlying mechanisms are still largely unclear. Dietary fibres are characterized by the fact that the pigU+2019s own enzymes are unable to digest them. Consequently, they pass through the stomach and small intestine to subsequently arrive at the level of the large intestine as substrate for the microbiota. For the older pig, the large intestines are well developed, and the microbiome herein capable to digest and ferment DF to a large extent (up to 70%), provided it is well adapted (U+2018primedU+2019) to the DF. A well-developed microbiome possesses a wide array of enzymes capable of digesting and fermenting DF. Dietary fibres consist of an array of chemical compounds, such as cellulose, hemicellulose, oligosaccharides, lignin, and pectin. Collectively, these compounds determine the physicochemical characteristics of DF and their effect in the GIT. Solubility, in this respect, is relevant as it is associated with the fermentability of the DF by the intestinal microbiota. On the other hand, an insoluble DF may exert maturational effects too, for instance through its bulking and abrasive effects in the GIT. However, a paucity of data exists on how, next to sow milk, DF in supplemental diet affects GIT maturation in suckling piglets. For this thesis we hypothesized that DF is important for early-life GIT maturation. Hence, the aim of this PhD was to evaluate the impact of DF enriched supplemental diets on GIT maturation in suckling pigs, including the capacity and functionality of stomach, small and large intestine, and the priming of GIT microbiota to ferment a typical post-weaning diet with plant-derived carbohydrates. The research questions deduced from this hypothesis were formulated in Chapter 2. A first study was performed to answer the question whether feral piglets start to ingest vegetable material from early life onwards and how this may be associated with GIT maturation (Chapter 3). To this aim, feral piglets were collected, and their age was estimated based on body size and their dentition. Stomachs were weighed and contents were examined to determine particle size distribution and to classify the diet items. Vegetable matter (mainly U+2018leaves and stemsU+2019) was predominantly present in most piglets, representing a large part of their diet (on average 83% of total stomach contents by weight). This was reported earlier for older wild boars and feral pigs. Approximately 25% of the stomachs of piglets contained curd (clotted sow milk) representing on average 16 % by weight. Other diet items (e.g., insects, fruits, seeds, mammals), were less abundant or absent. The data also indicated that a large proportion of their diets consisted of larger feed particles. The stomach development of the feral pigs appeared to be advanced when compared to stomach of farmed piglets of similar age fed a nutrient-dense, finely ground diet. We inferred from these data that feral suckling piglets consume a variety of non-milk items, mainly consisting of vegetable material with a coarse particle size from their first week of life onwards. Moreover, their diet is associated with an enhanced stomach development compared to those of farmed piglets. In a next experiment (Chapter 4), the effect of DF on GIT maturation in suckling piglets was studied. From day two of life onwards, sow suckled piglets were fed either a nutrient dense, low fibre control diet or diets enriched with two types of DF: a diet with a soluble fermentable DF from wheat; a diet with a largely non-fermentable purified cellulose, or a diet containing both DF sources. Piglets consumed the fibre-containing milk supplements and creep diets well. Upon weaning at 25 days of age, their GIT and large intestinal microbiota composition were evaluated. Stomach size and small intestinal maturation were not affected by diet. Large intestinal fill was increased with the soluble DF only. Large intestinal weight and length was increased in piglets consuming the fibrous diet; length mainly by the insoluble cellulose. Cellulose also decreased ileal pH and tended to increase ileal DM content compared to the control diet. Moreover, the concentration of volatile fatty acids tended to increase in the caecum and especially in the large intestine by supplementation with cellulose. The soluble DF source stimulated caecal propionate only. The microbiota composition showed a high individual variation and only limited dietary impact. Nonetheless, cellulose induced minor shifts in specific genera, with notable reductions of putative pathogens. It was concluded that the DF altered large intestinal morphology with little effect on the small intestine and stomach. Moreover, changes in the large intestine were associated with greater fermentation and changes of the microbiota, with more prominent effects from the low-fermentable cellulose. In Chapter 5, it was investigated whether piglets consuming fibrous supplemental diets prior to weaning were more resilient when exposed to an oral infection with enterotoxigenic E. coli (ETEC) one week after weaning. The suckling piglets were fed the same four supplemental diets as described for chapter 4. Upon weaning at approximately 25 days, piglets were fed the same low-fibre diet. Feed intake and body weight gain did not differ between treatments. Overall, indicators of GIT and general health of the piglets were similar between groups. Therefore, it was concluded that neither the supplementation of the soluble nor the insoluble DF source to the pre-weaning diet improved post-weaning growth or GIT health of piglets.In Chapter 6, the effect of inclusion of fine and coarsely ground oat hulls on gastrointestinal development of suckling pigs was studied. Piglets were fed one of three experimental diets. A finely ground low-fibre, nutrient dense diet served as control diet. For the high-fibre diets, heat-treated starch in the control diet was exchanged with finely or coarsely ground oat hulls. Oat hulls are a source of insoluble, slowly fermentable DF. The suckling piglets were fed the diets for approximately 3.5 weeks with their individual feed intake being recorded two times per day when separated from their dam. Feeding oat hulls did not impede clinical health or production performance of the piglets. The full stomach weights tended to be greater for the coarsely ground oat hulls compared to the finely ground oat hulls, whereas CON was intermediate. The coarse oat hulls increased GIT full weight and the weight of the caecum contents compared to piglets fed the control diet and the diet with finely ground oat hulls. Supplementing oat hulls increased villus height in the small intestines and dry matter concentration of the caecal contents. For the colon, inclusion of oat hulls increased its length, contents weight, short-chain fatty acid concentration and reduced total bacterial count as well as U+03B3-proteobacteria count and proportion. Furthermore, feeding the coarse oat hulls reduced colonic crypt depth when compared to the finely ground oat hulls. It was concluded that supplementing oat hulls to a diet for suckling piglets exerted subtle developmental effects on gastrointestinal morphology and colonic microbial community. These effects were largely independent from the particle size of the oat hulls. In the last experiment (Chapter 7), the growth performance and faecal consistency of piglets from birth to eight weeks of age was recorded with the objective to evaluate the inclusion of oat hulls in the diet during suckling and in the nursery period. From two weeks prior to weaning until two weeks after weaning (phase 1), the same diets were fed as described in chapter 6. For phase 2 of the study (day 14-28 after weaning), the inclusion level of oat hulls was decreased from 15% to 5%. The inclusion of oat hulls resulted in a reduction of the dietary net energy concentration by 12% and 4% for phase 1 and 2, respectively. The general health of all piglets remained good, based on the low morbidity and mortality rates. Pre-weaning feed intake and growth were not affected by diet. Overall, faeces score, body weight gain, feed intake and feed efficiency were similar across treatments. The overall net energy efficiency for weight gain was improved for pigs fed the oat hull diets. It was concluded that diluting pre- and post-weaning diets with oat hulls did not significantly influence performance in piglets. In summary, with DF supplementation of diets for suckling piglets it was possible to alter the maturation of the gastrointestinal tract and large intestinal microbiota. This was associated with greater fermentation activity in the large intestine. The magnitude of the observed changes were, however, subtle. Early feeding of DF may represent a U+2018window of opportunityU+2019, but its relevance for post-weaning resilience of the piglet needs to be further elucidated. Still, the work described in this thesis shows that young pigs can adapt to fibrous diets, even before weaning, confirming data in grower-fattener pigs and sows. Further work is warranted to optimize DF nutrition in the youngest category of pigs, both with respect to inclusion level as well as for the period during which fibrous diets are fed. Increasing our understanding of the diet of pigs in nature may advance the development of healthy diets as part of a sustainable pig production system with high welfare standards.

Jaar van publicatie:2022

Toegankelijkheid:Embargoed