Summarised by Rick Kleyn (SPESFEED (Pty) Ltd.) from Drikzwager, Veldman and Bikker, Animal Research: 54 231-236
Gut infection immediately post weaning is a problem in pigs. Previously, Post Weaning Syndrome (PWS) was mainly regarded as a disease with Escherichia coli as the monocausal agent. Currently PWS is regarded as a multi-factorial problem, with management, feed composition and hygiene all playing a role. In a recent article Drikzwager and co-workers deals with a nutritional approach to overcoming PWS.An important aspect of the resistance in the gut against PWS is a diverse and stabile microflora, by which “competitive exclusion” is generated and growth and attachment of (pathogenic) bacteria is counteracted. Newly weaned piglets may suffer from PWS because of the immature development of the gut and inadequate capacity to digest a “vegetable” diet. Gut damage is also caused by the weaning process. As a result, the colonisation resistance is disturbed and E. coli can proliferate and attach to the enterocytes.
In newly weaned piglets the gut can be damaged by the reduced feed intake immediately post weaning and the increased susceptibility for infections like Rota virus. Moreover, weaning itself is stressful. The villus height is reduced, crypt depth is increased, and the rate of mitoses is increased. In addition, the ability of the gut to digest a solid diet is inadequate. These processes result in mal-digestion, malabsorption and increased undigested food in the ileum. This substrate induces an explosive growth of bacteria and a disturbance of the colonisation resistance. Normally transient E. coli strains in the gut multiply and attach. The toxins produced by these bacteria are responsible for the PWS symptoms.
Specific measures with regards to feed composition and feeding strategy are discussed. These may have variable effects under practical conditions.
Improvement of gut development and prevention of gut damage at weaning:
When weaning occurs three or four weeks of age, it takes ten to 14 days before gut development matures enough to digest vegetable diets. In addition, the villus height is impaired because of low feed intake, infection, stress, etc. Feed and hence energy intake is often below the maintenance requirement for the five days after weaning. Thereafter feed intake increases but gut development remains inadequate. This creates an overload on the digestive system.
Gut damage immediately post weaning can be achieved by stimulating feed intake during day one to four post weaning and then control feed allowance from five to ten days after weaning. This implies that stimulation of feed intake before weaning is an important factor to prevent PWS. The measures that can be taken to prevent gut damage practice management are:
- Increase feed intake before weaning: supply a palatable diet to suckling piglets.
- Increase feed intake after weaning: use same diets before and after weaning. Soft pellets and wet diets have a positive effect on feed intake. The use of lights improves feed intake.
- Reduce gut damage supplying energy and growth factors to the enterocytes: e.g. butyrate, glutamine, nucleotides.
Improvement of digestion and absorption in the gut, reduction of the amount of substrate:
The impaired digestive and absorptive function of the gut can be (partly) compensated by the provision of highly digestible diets or by the addition of supplements stimulating digestion. These measures diminish the amount of substrate and reduce the risk of bacterial growth. The following can support improvement of the digestibility:
- Addition of enzymes, e.g. glucanases, xylanase and proteases.
- Technological treatment of the diets: the production of diets at higher temperature and pressure increases the digestibility of carbohydrates and fat in the diet.
- Use ingredients with a high nutrient content and high ileal and faecal digestibility.
- Piglet diets should contain low levels of crude protein and low levels of soluble NSP.
Inhibition of the growth of pathogenic bacteria:
Growth of Enterobacteriaceae like E. coli is inhibited below pH 4 (acid). Because of the faecal-oral recontamination, the stomach plays an important role in the infection cycle and an adequate function of the stomach.
Additives like organic acids and other measures with bacteriostatic or bacteriocidic may be used:
- Organic acids have a direct impact on increasing acidity of the gut. In addition, they have a bactericidal activity by disturbing the bacterial metabolism. They may improve stomach function, slow down stomach emptying rate, increase pancreatic enzyme production, and improve nutrient digestibility.
- The buffering capacity of the diet can be lowered, mainly by using a lower limestone levels and by reducing the crude protein content. This improves the stomach HCl production and the effectiveness of added organic acids.
- The addition of coarse particles, especially those containing indigestible fibre improves stomach function.
- Some essential oils may have bactericidal effects. There is still discussion as to which are effective and what the appropriate dosage is.
- Recent results indicate that medium chain fatty acids have potent bacteriostatic capacities.
Improvement of colonisation resistance:
A diverse and stabile microflora can prevent the growth and attachment of pathogenic bacteria. Bacteria regarded as beneficial create a less favourable gut environment or Enterobacteriaceae. Lactobacillae are regarded as positive bacteria as they produce lactic acid and bacteriocins which suppress the growth of E. coli. Improvement of colonisation resistance can be achieved as follows:
- Addition of high levels of positive bacteria (probiotics) e.g. Lactobacillae, certain Streptococcus strains in the diet or water.
- Prebiotics which are nutrients (e.g. inuline, mannan-oligo-saccharides) known to be substrates for Lactobacillae can fed.
- Ileal undigested residues from feed ingredients form the substrate for the growth of beneficial bacteria, e.g. resistant starch from potato and maize origin.
Decrease the attachment of bacteria and increase immune response:
Certain additives reduce the attachment of bacteria to enterocytes. The systemic and local immune response can be influenced by certain nutrients.
- Antibodies such as plasma proteins, egg powder, etc may be added to the diet.
- The sugar mannose may block glycoproteins and consequently reduce the attachment of Enterobacters.
- The immune response and cellular defence can be improved by ß-glucans, n-3 fatty acids, selenium, and vitamins A, D, E. Many of the feed additives mentioned, for example enzymes, probiotics, nucleotides etc. have variable effects under practical conditions. Factors influencing the effectiveness of these feed additives are the nature and amount of the substrate in the diet, the effective pH in the digestive tract, housing conditions and infection pressure from the environment. More insight and research is required for an appropriate evaluation and practical application of the measures mentioned.