What if live yeast could help ease the issues of weaning in piglets?
In 2006, when Europe started to ban antibiotic growth promoters, our swine experts were alerting pig professionals not to overlook the key role of digestive microbiota by these words: "the pig lives around its flora". Thirteen years later, the message seems to have come across the industry as we see gut health and digestive microflora balance gaining momentum. This seems all the more critical when looking at piglets around weaning, a key step of the production cycle that determines long-term welfare and performance. Let's see how in the past few year's technological advances such as metagenomics have helped to gain a better insight at the issues and stresses that surround weaning, and how these could be addressed in a context of antibiotic reduction.
Weaning: a stressful event
There is no doubt that weaning is one of the most stressful events in pig farming and represents a critical step which must be well managed in order to minimize production losses but also secure piglet health. In nature, weaning is a slow and gradual process, but today piglets are faced with a combination of stresses to which they must quickly adapt: diet, environment, social stress, maternal separation, etc. (Fig. 1). It is well known that the immediate consequence of weaning is a drastic reduction in feed intake. It has been shown that the interval between weaning and first meal can vary from a few minutes up to 60 hours, with up to 30% of non-eaters 24 hours post-weaning (Bruininx et al., 2002).
The source of digestive disorders
The stresses and sudden change of diet that happens at weaning can strongly impact the anatomy, functions and microbiota of the piglet gastro-intestinal tract, which in turn can be detrimental to an efficient digestive process and barrier function:
• First of all, low feed intake leads to an atrophy of digestive villi, hence a reduction of the gut absorption surface. This can impair nutrient assimilation and increase sensitivity to digestive pathologies (Berkeveld et al., 2009).
• In addition to reduced nutrient supply, the piglet ability to process those nutrients is also impaired. The newborn piglet is enzymatically equipped to digest milk, but poorly adapted to digest plant starch and proteins. For example, enzymes such as amylase and pepsine are not secreted at birth and their secretion is still far from optimal at six weeks. As a consequence, protein digestion is sub-optimal at weaning; feed conversion is less effective while digestive disorders can arise.
• Gut permeability, hence its barrier function is also affected at weaning. The epithelial cells that line the gut wall are sealed together by "tight junctions", which determine its impermeability to potential pathogens, preventing them from entering the gut tissue and blood supply. Weaning is a source of stress, translated by physiological reactions such as the release of cortisol. High level of cortisol will lead to the production of proinflammatory cytokines which is linked to the opening of the tight junctions, hence disrupting the digestive barrier function.
• Moreover, as the piglet moves away from colostrum, a source of immunoglobulins, its passive immunity is hindered while its own immune system is still fairly immature. At weaning, immune protection is sub-optimal and the piglet will be more sensitive to sanitary challenges.
• The piglet, its gut and its microbiome are intimately linked. The impact that weaning has on the piglet physiology and digestion is reflected at the microbiota level. Until recently, piglet microbiota was under-studied, scientists relying mainly on traditional microbial culture techniques. Today, thanks to genetic based techniques, it is possible to get a better insight of these microbial populations, especially minor populations or those that could not be cultured in the lab with traditional techniques. Recent studies have shown the important impact of weaning on the piglet gut microbiota profile (Yang et al, 2015, Frese et al. 2015). Frese attributes the changes during weaning to the sudden diet transition: from a milk-oriented microbiome, prone to digest milk sugars, to an increased population of saccharolytic microbes and an increase in populations expressing fiber degrading bacteria. This is further illustrated by a study conducted with the University of Nottingham where King et al. showed a reduced bacterial diversity at weaning (Fig. 2), linked to an increase in fecal E. coli abundance and diarrhea post-weaning (King et al., 2016).
This microbiota switch can be explained by the sudden change in feed material, as well as other factors such as feed intake drop. Indeed, after a potential fasting period, when piglets start eating again, the dramatic increase of intake can overcome the gut capability (impaired villosity). Partially digested feed can enter the colon, where undesired fermentations can occur, leading to dysbiosis, explaining the frequently observed post-weaning diarrheas(PWD). Pathogenic Escherichia coli plays a great role in the occurrence of PWD in the first two weeks after weaning. It is typically associated with dehydration, loss of body condition and increased mortality.
How to manage gut microflora and inflammation?
In a context of reduced antibiotic usage in piglet feed, other management strategies are sought to answer the challenges of weaning and associated morbidity such as PWD. A stack of evidence indicates that a pro-biotic approach, as opposed to an anti-biotic one is a virtuous answer to help at several levels. In particular, live yeast Saccharomyces cerevisiae boulardii, extensively documented in human and animals, has been shown to act at three levels in the gut: it helps improve microbiota balance, gut morphology and immunity (Fig. 3).
3rd line of defense:
New microbiota studies (King et al., 2016) indicate that piglet supplementation with Saccharomyces cerevisiae boulardiiCNCM 1-1079 appear to preserve microflora diversity around weaning. Supplemented piglets showed a greater proportion of Lactobacillipopulation. Antibiotic treatments profoundly affected the gut microbiota of weaned piglets (as expected), while administration of the live yeast maintained and stabilized the microbiota structure during antibiotic treatment. Similar findings came from a recent Canadian study (Brousseau et al., 2015). The authors showed that antibiotic treatment significantly reduced ileal microbiota diversity two weeks post-weaning and promoted the establishment of Firmicutes, while S. c. boulardiiCNCM 1-1079 consumption positively influenced the establishment of the Porphyromonadaceaeand Ruminococcaceaebacterial families in the colon of the piglets (Fig. 4).
• The live yeast supplementation leads to increased villi size and gut absorption surface (Bontempo et al., 2006).
• It was shown to maintain tight junction closed and reduces gut permeability as well as pathogens translocation from the gut, such as E. coli (Lessard et al., 2009 ).or Salmonella.
• At the immune response level, the live yeast helps control the inflammatory response and contributes to gut immune defenses, leading to increased survival under LPS challenges (Collier et al., 2011).
• Thanks to powerful genetic approach (transcriptomic), the intense stress of weaning could also be visualized at the level of gene expression in the piglet gut (Le Bon et al., 2015). The study, conducted in partnership with University of Nottingham, indicated that the expression of more than 1,000 intestinal genes was affected by weaning, in particular genes involved in the inflammatory response, defense against pathogens and the degradation of host tissues. In this study, when piglets received the probiotic around weaning, the number of genes affected by weaning was reduced by a staggering 60%. Most importantly, none of the genes related to inflammation or tissue degradation which were activated by weaning appeared to be up-regulated when the probiotic was used (Fig. 5).
This indicates that weaning entails important changes in gut gene expressions, and that the live yeast help alleviate these changes, suggesting a protective role on the gut barrier function and immunoregulation.
From the gut to the farm
These scientific findings are correlated to performance results and recurrent feed-backs from the field, reporting positive effect on morbidity (post-weaning diarrheas), and performance. For example, a recent trial (Savoini et al., University of Milan, unpublished, 2016) conducted in post-weaning piglets (day 0-50) show a positive effect of this particular probiotic on piglets' zootechnical performance: average daily gain and feed efficiency were improved in all phases by respectively +5.59% and -4.97% (Table 1).
In conclusion, weaning represents a major challenge for the piglet digestive microbiota, but it is not the only one. Studies have shown that interventions such as the use of antibiotics or probiotics can further impact microflora profile: while antibiotic lead to a poorer microbial diversity, probiotic seems to help maintain a healthy microflora while also affecting gene expression within the gut itself.
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Article made possible through the contribution of Lallemand