A holistic nutritional concept to enhance gut health and performance of young pigs

A healthy gut with balanced gut microbiota is essential because inflammation of the gut leads to immune activation coupled with increased energy expenditures and compromised digestion and absorption of nutrients.

Gut health – particularly important for weaned pigs

Post-weaning diarrhoea is caused by multiple factors, including excess indigestible protein, an immature digestive tract, and the proliferation of pathogenic bacteria. Pig producers pay special attention to post-weaning diarrhoea because it increases medication and animal mortality, reduces growth performance, and lowers profitability. According to the meta-analysis, bacterial infections of the gut are the main cause of reduced performance in weaned pigs – with weight gain reduced by up to 40% compared to healthy pigs.

The use of in-feed antimicrobial growth promoters and zinc oxide (ZnO) have been effective in controlling post-weaning diarrhoea. However, since the ban of antimicrobial growth promoters and ZnO in Europe and other countries, post-weaning diarrhoea has become more challenging for the swine industry.

Benefits of low-protein adequate diets on gut health

Diets fed to weaned pigs usually contain high crude protein (CP) levels because of a higher amino acid requirement (% of diet) and a lower capacity for feed intake compared with growing pigs. The digestive organs of weaned pigs are still immature, resulting in lower digestibility of protein and amino acids. Consequently, feeding high CP diets leads to greater amounts of undigested protein in the hindgut, causing the proliferation of pathogenic bacteria, e.g., E. coli, which increases the incidence of post-weaning diarrhoea and contributes to more nitrogen and ammonia emissions to the environment.

Figure 1 – The effect of nitrogen (N) intake (g/d) on the incidence of post-weaning diarrhoea in weaned pigs

Feeding low CP diets directly reduces the proliferation of pathogenic bacteria and post-weaning diarrhoea in weaned pigs. For example,  it was observed that a marked reduction in E. coli counts from ileal mucosa of weaned pigs subjected to an E. coli K88+ challenge by reducing the dietary CP content from 22% to 17%. The study showed that post-weaning diarrhoea incidence could be reduced by feeding a low CP (19%) diet compared to a high (25%) CP diet under both non-challenged and ETEC K88 challenged conditions (Figure 1).

In another study, pigs fed a low CP (17.3%) diet for a relatively short period of 5 days after weaning was sufficient to decrease incidences of post-weaning diarrhoea compared to pigs fed a high CP (24.3%) diet. Therefore, reducing the CP level of the diet is often one of the first steps nutritionists take as part of the nutritional strategy for weaned pigs.

Effects of probiotics on gut health and performance of weaned pigs

Probiotics (live microorganisms) are one of the functional feed additives used to improve gut health. Some of the mechanisms by which probiotics work include:

1. Direct inhibition of pathogen growth by the secretion of antimicrobial substances.
2. Modulation of resident microbiota composition and activity.
3. Stimulation of the host immune system and improvement in intestinal barrier function.

Most probiotics are based on bacteria (Bacillus-based and lactic acid-producing) and yeasts. Bacillus strains have advantages as they can form endospores and are resistant to heat processing and harsh conditions (such as bile acids) in the gut.

GutPlus (Bacillus subtilis 32540) and GutCare (Bacillus subtilis 32315) are probiotics specially developed by Evonik to inhibit pathogens, including E. coli F18 and C. perfringens, respectively, and produce secondary (antimicrobial) metabolites and lactic acid. They are also compatible with organic acids and antimicrobial growth promoters. Numerous studies show the beneficial effects of probiotics on the gut health of pigs.

A study conducted at the University of California, Davis, showed that supplementation with GutPlus resulted in greater body weight (day 7, 12 and 21) and a reduction in the frequency of severe diarrhoea (score >4) in pigs under E. coli F18 challenge (Figure 2). They also observed an increase in the number of goblet cells in the duodenum, as well as a greater mucin area in the villi of jejunum.

Figure 2 – The effect of GutPlus on diarrhoea and growth of weaned pigs challenged with E. coli F18 

Meanwhile, a recent study conducted at the research farm of PigChamp in Spain compared the effect on weaned pigs of supplementing their diet with GutCare combined with a pharmacological dose of ZnO for 35 days, divided into 2 phases (Pre-starter: day 0-14; Starter: day 15-35). ZnO was added to the diets only from days 0 to 14.

In terms of body weight gain, the results showed that supplementation with GutCare increased the average daily gain of pigs during all phases (compared to the basal diet). Meanwhile, ZnO addition increased average daily gain during the Pre-starter and Overall phase (Figure 3). ZnO also greatly reduced incidences of diarrhoea during both Pre-starter and Starter phases (compared to the basal diet), while pigs fed GutCare were intermediate. These results indicate that GutCare may replace ZnO under normal conditions.

Figure 3 – The effect of GutCare or ZnO on diarrhoea and body weight gain of weaned pigs 

Combination of low protein diets with probiotics

An earlier study reported that the addition of probiotics in a low CP diet resulted in the greatest average daily gain in weaned pigs challenged with E. coli compared to the addition of probiotics to a high CP diet.

Evonik also conducted a 42-day study at the facility of Sichuan Agricultural University to determine the effect of combining GutCare with a high and low CP diet. Both average daily gain and gain:feed ratio increased with probiotics addition but interestingly the best performance was achieved by combining GutCare with a low CP diet (Figure 4).

The greatest villus height to crypt depth (VH:CD) ratio as well as gene expression of tight junction proteins in the ileum were observed in pigs fed the low CP diets supplemented with GutCare, indicating a possible synergistic effect of combing low CP with probiotics. This may be because probiotics can out-grow in the gut better when the proliferation of pathogenic bacteria is reduced due to less undigested substrate from a lower CP content in the diet.

Figure 4 – The effect of dietary CP level and GutCare addition on performance and gut morphology of weaned pigs

Combination of fibres with probiotics

Dietary fibre is plant-derived polysaccharides resistant to enzymatic digestion in the small intestine but serves as a substrate for bacterial fermentation mainly in the hindgut intestine. Due to its physicochemical properties such as solubility, viscosity and water-holding capacity, dietary fibre interacts with the microflora and the mucosa in the gut, affecting passage rate and ultimately gut health.

High levels of both insoluble and soluble fibre had negative effects on gut health and nutrient digestion, while a moderate dietary inclusion of insoluble fibre or in combination with soluble fibre seems to have beneficial effects on gut health.

Figure 5 – The effect of dietary fibre types and GutCare addition on performance and E. coli count in cecum of weaned pigs

A study was conducted at PigChamp research farm, Spain, to evaluate the effect of fibre types (sugar beet pulp as fermentable fibre and wheat bran as insoluble fibre) with or without GutCare on the performance and gut health of weaned pigs for a period of 21 days.

Pigs fed sugar beet pulp had increased performance, and less caecal E. coli counts compared with those fed wheat bran (Figure 5). Dietary supplementation with GutCare increased gain:feed ratio and reduced E. coli in cecum regardless of which fibre sources they were fed.

Overall, the combination of GutCare with sugar beet pulp enhances the growth and intestinal health of piglets immediately post-weaning.

Conclusion

Based on these results, supplementation with probiotics GutPlus and GutCare in diets for weaned pigs can improve gut health, decrease diarrhoea incidences, and improve the performance of weaned pigs similar to the levels achieved with antibiotics. Reducing dietary crude protein may act synergistically with probiotics to further improve gut health, pig performance and reduce nitrogen excretion. Therefore, a holistic approach of combining low CP diets, probiotics and fermentable fibres should be considered as part of an antibiotic growth promoter-free gut health concept towards more sustainable pig production.

References upon request.