J.R. Pluske

Factors influencing the structure and function of the small intestine in the weaned pig: a review

At weaning, the young pig is subjected to myriad of Stressors (e.g. change in nutrition, separation from mother and littermates, new environment) which cause reduced growth. This post-weaning ‘growth check’ continues to represent a major source of production loss in many commercial piggeries. Associated with weaning are marked changes to the histology and biochemistry of the small intestine, such as villous atrophy and crypt hyperplasia, which cause decreased digestive and absorptive capacity and contribute to post-weaning diarrhoea. In this review we have outlined the major factors implicated in the aetiology of these changes, such as the role of enteropathogens, transient hypersensitivity to dietary antigens, and the withdrawal of milk-borne, growth-promoting factors. Special attention has been paid to the role of food (energy) intake as a mediator of intestinal structure and function after weaning, although other influences such as the source of protein added to the diet may interact with food intake to alter gut structure and function. This is clearly an area of production concern, and future research into areas such as manipulation of the immature digestive tract with exogenous growth factors and (or) dietary supplementation with ‘non-essential’ amino acids such as glutamine, appear warranted.

A review of interactions between dietary fibre and the intestinal mucosa, and their consequences on digestive health in young non-ruminant animals

The maintenance of gut health is complex and relies on a delicate balance between the diet, the commensal microflora and the mucosa, including the digestive epithelium and the overlying mucus layer. Superimposed on this balance is the frequent presence of enteric bacteria with pathogenic potential, the proliferation and metabolic activity of which may perturb digestive function, and lead to diarrhoea, poor growth rates and even death. Such enteric infections with pathogenic bacteria are common in young animals and children. Diet has an important influence on gut health, including effects on proliferation of pathogenic bacteria, and it can provide either beneficial or harmful input. Dietary fibre (DF) is a dietary component that has a major influence in this regard. DF is a heterogeneous class of components that are not hydrolysed by digestive enzymes of non-ruminant animals, and consequently are the main substrates for bacterial fermentation in the distal part of the gut. This review presents evidence that some components of dietary fibre may improve gut health, or alternatively enhance gut perturbation and subsequent diarrhoea in young animals (including piglets, chickens and children). This review reports and discusses how DF interacts with the gut epithelium and mucus, directly or by the way of the microflora, and consequently can protect against or enhance enteric infections.

Gastrointestinal health and function in weaned pigs: a review of feeding strategies to control post-weaning diarrhoea without using in-feed antimicrobial compounds.

For the last several decades, antimicrobial compounds have been used to promote piglet growth at weaning through the prevention of subclinical and clinical disease. There are, however, increasing concerns in relation to the development of antibiotic-resistant bacterial strains and the potential of these and associated resistance genes to impact on human health. As a consequence, European Union (EU) banned the use of antibiotics as growth promoters in swine and livestock production on 1 January 2006. Furthermore, minerals such as zinc (Zn) and copper (Cu) are not feasible alternatives/replacements to antibiotics because their excretion is a possible threat to the environment. Consequently, there is a need to develop feeding programs to serve as a means for controlling problems associated with the weaning transition without using antimicrobial compounds. This review, therefore, is focused on some of nutritional strategies that are known to improve structure and function of gastrointestinal tract and (or) promote post-weaning growth with special emphasis on probiotics, prebiotics, organic acids, trace minerals and dietary protein source and level.

Environmentally-acquired bacteria influence microbial diversity and natural innate immune responses at gut surfaces

BackgroundEarly microbial colonization of the gut reduces the incidence of infectious, inflammatory and autoimmune diseases. Recent population studies reveal that childhood hygiene is a significant risk factor for development of inflammatory bowel disease, thereby reinforcing the hygiene hypothesis and the potential importance of microbial colonization during early life. The extent to which early-life environment impacts on microbial diversity of the adult gut and subsequent immune processes has not been comprehensively investigated thus far. We addressed this important question using the pig as a model to evaluate the impact of early-life environment on microbe/host gut interactions during development.ResultsGenetically-related piglets were housed in either indoor or outdoor environments or in experimental isolators. Analysis of over 3,000 16S rRNA sequences revealed major differences in mucosa-adherent microbial diversity in the ileum of adult pigs attributable to differences in early-life environment. Pigs housed in a natural outdoor environment showed a dominance of Firmicutes, in particular Lactobacillus, whereas animals housed in a hygienic indoor environment had reduced Lactobacillus and higher numbers of potentially pathogenic phylotypes. Our analysis revealed a strong negative correlation between the abundance of Firmicutes and pathogenic bacterial populations in the gut. These differences were exaggerated in animals housed in experimental isolators. Affymetrix microarray technology and Real-time Polymerase Chain Reaction revealed significant gut-specific gene responses also related to early-life environment. Significantly, indoor-housed pigs displayed increased expression of Type 1 interferon genes, Major Histocompatibility Complex class I and several chemokines. Gene Ontology and pathway analysis further confirmed these results.ConclusionEarly-life environment significantly affects both microbial composition of the adult gut and mucosal innate immune function. We observed that a microbiota dominated by lactobacilli may function to maintain mucosal immune homeostasis and limit pathogen colonization.

Restricting microbial exposure in early life negates the immune benefits associated with gut colonization in environments of high microbial diversity.

Background Acquisition of the intestinal microbiota in early life corresponds with the development of the mucosal immune system. Recent work on caesarean-delivered infants revealed that early microbial composition is influenced by birthing method and environment. Furthermore, we have confirmed that early-life environment strongly influences both the adult gut microbiota and development of the gut immune system. Here, we address the impact of limiting microbial exposure after initial colonization on the development of adult gut immunity. Methodology/Principal Findings Piglets were born in indoor or outdoor rearing units, allowing natural colonization in the immediate period after birth, prior to transfer to high-health status isolators. Strikingly, gut closure and morphological development were strongly affected by isolator-rearing, independent of indoor or outdoor origins of piglets. Isolator-reared animals showed extensive vacuolation and disorganization of the gut epithelium, inferring that normal gut closure requires maturation factors present in maternal milk. Although morphological maturation and gut closure were delayed in isolator-reared animals, these hard-wired events occurred later in development. Type I IFN, IL-22, IL-23 and Th17 pathways were increased in indoor-isolator compared to outdoor-isolator animals during early life, indicating greater immune activation in pigs originating from indoor environments reflecting differences in the early microbiota. This difference was less apparent later in development due to enhanced immune activation and convergence of the microbiota in all isolator-reared animals. This correlated with elevation of Type I IFN pathways in both groups, although T cell pathways were still more affected in indoor-reared animals. Conclusions/Significance Environmental factors, in particular microbial exposure, influence expression of a large number of immune-related genes. However, the homeostatic effects of microbial colonization in outdoor environments require sustained microbial exposure throughout development. Gut development in high-hygiene environments negatively impacts on normal succession of the gut microbiota and promotes innate immune activation which may impair immune homeostasis.

Feed- and feed additives-related aspects of gut health and development in weanling pigs

The development of new/different management and feeding strategies to stimulate gut development and health in newly-weaned pigs, in order to improve growth performance while minimizing the use of antimicrobial compounds such as antibiotic growth promotants (AGP) and heavy mineral compounds, is essential for the long-term sustainability of the pig industry. Factors including the sub-optimal intake of nutrients and energy, inappropriate microbiota biomass and (or) balance, immature and compromised immune function, and psychosomatic factors caused by weaning can compromise both the efficiency of digestion and absorption and intestinal barrier function through mucosal damage and alteration of tight junction integrity. As a consequence, pigs at weaning are highly susceptible to pathogenic enteric conditions such as post-weaning diarrhea that may be caused by serotypes of enterotoxigenic Escherichia coli. Many dietary components, e.g., protein, fiber, feed additives and minerals, are known to influence microbial growth in the gastrointestinal tract that in turn can impact upon pig growth and health, although the relationships between these are sometimes not necessarily apparent or obvious. In a world climate of increased scrutiny over the use of antibiotics per se in pig production, certain feed additives are seen as alternatives/replacements to antibiotics, and have evolved in some cases to have important roles in everyday commercial pig nutrition. Nevertheless and in general, there remains inconsistency and variability in the efficacy of some feed additives and in cases of severe disease outbreaks, for example, therapeutic antibiotics and/or heavy minerals such as zinc oxide (ZnO) are generally relied upon. If feed ingredients and (or) feed additives are to be used with greater regularity and reliability, then it is necessary to better understand the mechanisms whereby antibiotics and minerals such as ZnO influence animal physiology, in conjunction with the use of appropriate challenge models and in vitro and in vivo techniques.

A chemical analysis of samples of crude glycerol from the production of biodiesel in Australia, and the effects of feeding crude glycerol to growing-finishing pigs on performance, plasma metabolites and meat quality at slaughter

Theaimsofthisstudywereto:(i)determinethechemicalcompositionof11samplesofcrudeglycerolcollected from seven Australian biodiesel manufacturers; and (ii) examine the effects of increasing levels of crude glycerol fed to growing-finishing pigs on performance, plasma metabolites and meat quality at slaughter. Chemical composition of crude glycerol samples varied considerably; glycerol content ranged between 38 and 96%, with some samples containing up to 29% ash and 14% methanol. One of these samples (76.1% glycerol, 1.83% methanol) was then fed to 64 female pigs (50.95.55kg;means.d.)allocatedtooneof fivedietarytreatments(0,4,8,12and16%crudeglycerol)untiltheyreached 105 kg liveweight. There were no statistical differences in performance indices with increasing levels of added glycerol, althoughtherewasanunexpectedlyhighvariationbetweentreatments.Bloodglycerollevelswereunaffectedbydietinweek two of the experiment, but increased linearly (P 0.05).Dietscontainingaddedcrude glycerolwerelessdustyaftermixing,butdietsthatcontained8,12and16%glycerolallformeda firmaggregatewithin24hof mixing that presented some feeding difficulties. This might restrict inclusion of glycerol in mash diets to dietary levels less than8%.Furthermore,levelsofresiduessuchasmethanolandashshouldbemonitoredtopreventexcessiveamountsofthese compounds in pig diets.

Weaning the pig: concepts and consequences

Weaning the Pig: Concepts and Consequences addresses the major issues surrounding the weaning process, both for piglets and the breeding herd, in modern-day pig production. The post-weaned pig presents many challenges to the manager, stockperson and nutritionist, and as such is a critical phase in the overall production system. Numerous challenges are also faced by the sow, which is required to be rebred as soon as possible after weaning. This book draws together summaries of research dealing with both piglets and the sow. Accordingly, the material presented covers the following areas associated with the weaning process: growth of the weaned pig, nutritional management in preparation for weaning, behavioural changes and adaptations around weaning, voluntary feed intake, digestive physiology, modulation of small intestinal integrity, the intestinal microflora and diarrhoeal diseases after weaning, intestinal immunity, nutritional requirements and intestinal requirements of the weaned pig, environmental and housing issues after weaning, saving and rearing supernumery and underprivileged piglets, and productivity and longevity of the weaned sow.

Feeding a diet with decreased protein content reduces indices of protein fermentation and the incidence of postweaning diarrhea in weaned pigs challenged with an enterotoxigenic strain of Escherichia coli

This study evaluated the effect of feeding low protein (LP) diets for 7 or 14 d after weaning or a high protein (HP) diet for 14 d after weaning on postweaning diarrhea (PWD), indices of protein fermentation, and production in pigs infected or not infected per os with an enterotoxigenic strain of Escherichia coli. A total of 72 female pigs weaned at aged 21 d with initial BW of 5.9 +/- 0.12 kg were used in a 3 x 2 factorial arrangement of treatments. The factors were 3 feeding regimens associated with different combinations of feeding duration and diet CP level: (i) HP diet (256 g of CP/kg) fed for 14 d after weaning, (ii) LP diet (175 g of CP/kg) fed for 7 d after weaning, and (iii) LP diet fed for 14 d after weaning; and infection or noninfection with an enterotoxigenic strain of E. coli (10(7) cfu/mL, serotype O149:K91:K88) at 72, 96, and 120 h after weaning. The LP diets were fortified with crystalline Ile and Val to achieve an ideal AA pattern. A second-stage diet (213 g of CP/kg) was fed to pigs at the conclusion of each feeding regimen, and the study finished 4 wk after weaning. None of the diets contained antimicrobials. Feeding the LP diets decreased (P < 0.001) plasma urea nitrogen, fecal ammonia nitrogen concentrations, and the incidence of PWD, but increased (P = 0.001) fecal DM content compared with pigs fed HP in the 2-wk period after weaning. Infection increased shedding of beta-hemolytic E. coli (P < 0.001), the incidence of PWD (P < 0.001), and fecal ammonia nitrogen concentrations (P < 0.01), but did not interact with feeding regimen, after weaning. Pigs challenged with E. coli grew more slowly (P < 0.001) and had decreased G:F (P < 0.01) compared with nonchallenged pigs in the 4-wk period after weaning. Feeding an LP diet for 7 or 14 d after weaning markedly reduced the incidence of PWD after infection with beta-hemolytic E. coli. Infection was associated with decreased indices of protein fermentation in the distal gastrointestinal tract but did not compromise the growth of weaner pigs in the 4-wk period after weaning.

Establishment of normal gut microbiota is compromised under excessive hygiene conditions

Background Early gut colonization events are purported to have a major impact on the incidence of infectious, inflammatory and autoimmune diseases in later life. Hence, factors which influence this process may have important implications for both human and animal health. Previously, we demonstrated strong influences of early-life environment on gut microbiota composition in adult pigs. Here, we sought to further investigate the impact of limiting microbial exposure during early life on the development of the pig gut microbiota. Methodology/Principal Findings Outdoor- and indoor-reared animals, exposed to the microbiota in their natural rearing environment for the first two days of life, were transferred to an isolator facility and adult gut microbial diversity was analyzed by 16S rRNA gene sequencing. From a total of 2,196 high-quality 16S rRNA gene sequences, 440 phylotypes were identified in the outdoor group and 431 phylotypes in the indoor group. The majority of clones were assigned to the four phyla Firmicutes (67.5% of all sequences), Proteobacteria (17.7%), Bacteroidetes (13.5%) and to a lesser extent, Actinobacteria (0.1%). Although the initial maternal and environmental microbial inoculum of isolator-reared animals was identical to that of their naturally-reared littermates, the microbial succession and stabilization events reported previously in naturally-reared outdoor animals did not occur. In contrast, the gut microbiota of isolator-reared animals remained highly diverse containing a large number of distinct phylotypes. Conclusions/Significance The results documented here indicate that establishment and development of the normal gut microbiota requires continuous microbial exposure during the early stages of life and this process is compromised under conditions of excessive hygiene.