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Optimum stomach function W
eaning of piglets is a stressful event. The low feed intake and stress caused by the weaning process result in damage to the intestinal wall and subsequently compromise immune response. The piglet’s feed intake starts to increase again from around one
week post-weaning. However, the digestive capacity of the intestine is insufficient because of the damage and because the digestive tract is not yet fully developed. Undigested nutrients will reach the large intestine and promote the proliferation of bacteria. Fermenting undigested protein can be especially dangerous due to the proliferation of Escherichia coli, and the adverse effects of fermentation products further increase the permeability of the intestinal wall. At weaning, a combination of low HCl secretion and the consumption of large meals at infrequent intervals can result in elevated pH, often to over 5.0, and it may remain high for several days. The high acid-binding/buffering capacity of the feed (its ability to neutralise acid) helps to further raise stomach pH, which results in reduced digestion; feed will then be fermented in the hind gut and may pro- voke diarrhoea. A high gastric pH will also allow pathogens to survive and gives them greater opportunity to colonise the digestive tract. The gastric pH can be manipulated by the acid-binding capacity (ABC) of the diet. The ABC is defined as the ability of a feedstuff to resist a pH change. The ABC is usually measured as the milliequivalents (mEq) acid or base needed to change the pH of the feedstuff to the pH end-titration. If the pH of the feedstuff is lower than the pH end-titration point, a base is used and the ABC value is negative. Ingredients with a high ABC will have a stronger effect on neutralising the pH in the stomach than ingredients with a low ABC. Depending on the method of analysis, acid ingredients can have a negative ABC and will have a strong- er effect on decreasing the stomach pH compared to ingredients with a positive ABC. Taking the ABC into account when formulating diets can help when choosing ingredients and additives that will not have a great neutralising effect on stomach pH. The ABC-4 at dietary level can be manipulated by different factors such as the crude protein level of the diet or the protein sources, the mineral sources and levels, or the addition of organic acids in post-weaning di- ets. Moreover, the physicochemical characteristics of the diet can also influence its stomach retention and therefore also have an effect on reducing the ABC-4 of the diet. Based on research conducted in Schothorst Feed Research we can conclude that immediately post-weaning the ABC-4 should be lower than 250–300 mEq/kg. This will result in a low stomach pH that will function as a natural barrier, lowering the chance for pathogens to pass the stomach and reach the intestine. Also, a lower stomach pH has a positive effect on protein digestion. And finally, a low stom- ach pH reduces the rate of emptying of the stomach, which also has a positive effect on diet digestibility.
Francesc Molist
holds a PhD in animal nutrition from the Universitat Autònoma de Barcelona in Spain. He has been working for Schothorst Feed Research in the Nether- lands since 2011, most recent- ly as manager research & development.
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