Weaning is a stressful event in the life of a pig, with a combination of environmental, social and nutritional adjustments for the piglet to deal with and the potential for illness or even mortality as a result of diarrhea. With restricted use of antibiotics, or complete bans in some countries, researchers are actively pursuing alternative feeding strategies. Researchers are also making considerable efforts to determine what conditions are necessary to optimize the gastrointestinal (GI) ecosystem to prevent the major intestinal diseases in the first place.
The GI tract is a very complex organ and its health and development hold the key to productivity in all domestic livestock and poultry. The tract has two basic functions that are essential to growth and development:
- acquiring and absorbing nutrients, and
- maintaining a barrier of protection against infection from microorganisms and viruses.
What changes occur in weaned piglets that predispose them to disease? At weaning, the piglet’s diet dramatically changes from sow’s milk to a solid ration so the gut microbes have to adapt very quickly. The change of diet usually results in reduced feed intake, below the maintenance requirement, during the first week. This low level of intake has a negative impact on the structure of the small intestine, resulting in shortening of the villi (fine projections that increase the surface area and absorptive capacity of the gut). The degeneration of the villi in the small intestine is considered a predisposing factor for postweaning health problems.
Some of the most prominent intestinal diseases in pigs include:
Postweaning colibacillosis is the most common intestinal disorder in pigs immediately post-weaning and is associated with the rapid growth of toxin-producing E. coli in the small intestine.
Swine dysentery is a form of colitis affecting the caecum, colon and rectum of grower pigs and is one of the most economically important intestinal diseases in swine.
Salmonellosis is a concern in the swine industry for two reasons: 1) clinical disease of pigs and 2) contamination of pig products with Salmonella serotypes that can infect humans.
Porcine proliferative enteropathies (AKA ileitis) can be acute or chronic conditions with a common underlying pathological change visible as a thickening of the mucosa of the small intestine and colon (garden hose gut). Economic losses associated with ileitis can result from poorer feed conversion, longer days to market, increased mortality and higher cull rates.
Gastric ulcers in the stomach are common in slaughter pigs and the lesions cause reduced growth performance.
Endo-parasite infection in grower finisher pigs can have major economic impact on pig production through reduced performance. At low levels of infection, parasites like Ascaris suum (roundworms) are known to reduce average daily gain and feed conversion and can even cause mortalities at higher levels.
Recent research in Denmark has focussed on feeding strategies to enhance intestinal function in pigs. To date, the most successful strategies being used include manipulation of feed composition as well as the use of fermented liquid feed, coarse non-pelleted feed, and organic acids.
Danish researchers suggest that the single most important control for the ecosystem in the GI tract, and ultimately for pig health, is the amount and type of substrate available to the microbial population. In theory, this would allow direct control over the processes of fermentation in the GI tract through feed composition. Results to date are inconsistent but studies have focussed on how the fiber, protein and fat content of the diet affect microbial fermentation.
Fermented liquid feed has been a hot topic in Europe over the past 5 years as they have searched for alternatives to antibiotics. Feeding fermented liquid feed reduces the pH in the stomach to four or less, which inhibits the growth of bacteria such as coliform and Salmonella, and prevents diarrhea. However, growth performance is not improved by feeding fermented liquid feed, although systems where only the grain is fermented show promise. This may be due to associated improvements in the gut structural components. Results from piglets fed a liquid diet with fermented wheat showed they had higher villus height and higher villus:crypt ratio, suggesting that this may be a way to prevent degeneration of the mucosal architecture after weaning.
Feed processing methods are another factor to be considered. Feeding slaughter pigs coarsely ground feed compared to fine pelleted feed reduces pH of the stomach contents and significantly increases the concentration of organic acids (such as lactic, acetic, propionic and butyric acid) in the stomach. This favors the growth of anaerobic bacteria in the stomach, which in turn produce organic acids. An obvious drawback with feeding a coarse ration is the reduction in performance results – this obviously has to be a consideration when using this strategy.
Adding organic acids to the diet results in inconsistent effects on GI ecology of pigs, depending on the acid and dose used. The pH along the GI tract tends to be lower after addition of organic acids but often the effect is not significant. In general, organic acids have a negative impact on bacteria along the GI tract while growth performance is positively affected, with variable results depending on the type of acid and diet used, as well as the dose employed. It is important to note that besides the option to add acids directly to the diet, the effect can be simulated through strategies like fermented liquid feeding or feeding coarse diets, resulting in increased levels of organic acids in the stomach.
The use of fermented liquid feed, coarse non-pelleted feed and organic acids lowers the pH in the stomach, killing off bacteria like E. coli and Salmonella so that they do not enter parts of the GI tract where they normally grow and multiply. In this capacity, the stomach acts as a barrier to break the vicious cycle where animals become a source of infection to themselves and others.
Danish researchers suggest that sufficient feed intake is THE most important factor in maintaining performance and health of piglets post-weaning. Piglets that consume creep feed in the farrowing stall are more likely to make the transition early to post-weaning feed intake. The best way to increase feed intake during the nursing phase, to limit problems in the transition phase and beyond, is to increase weaning age from four to five weeks of age (according to experience in Denmark).
Source: Jensen, BB, Hojberg, O, Mikkelsen, LL, Hedemann, MS, and Canibe, N. 2003. Enhancing intestinal function to treat and prevent intestinal disease. Proceedings of the 9th International Symposium on Digestive Physiology in Pigs. May 14-17, 2003.
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|Author:||Greg Simpson – Swine Nutritionist/OMAFRA|