Microbial balance and optimal digestion in pigs

By Peter Kürti DVM, Chr. Hansen

Compared to the total number of microorganism species inhabiting the intestinal ecosystem, only a few are able to cause an upset of the microbial balance that can result in disease. In the healthy pig the intestinal balance is based on the constant competition between bacteria for space and nutrients within the lumen of the intestines.
calendar icon 3 March 2006
clock icon 7 minute read
Chr. Hansen - BioPlus 2B

Harmless and potentially pathogenic bacteria keep each other in check. When external influences, for example stress or sudden change in nutrient sources, occur this balance can be upset and potential pathogenic bacteria dominate their harmless counterparts in sections of the intestines. This can result in disease or suboptimal growth.

As far as profitability of pig production is concerned, the most devastating effect of the disturbed microbial balance in the intestines is diarrhoea. This occurs mainly at the time around weaning or in the periods of sudden change in feed. Under normal conditions potential pathogen bacteria are present in very low numbers in the intestines. Their specific counterparts, bacteria that need the same habitat or have identical nutrient requirements, are also present in low numbers, compared to the total number of intestinal bacteria.

Whether stress or changes in feed cause diarrhoea, generally depends on how potential pathogens, for example E. coli, are able to outcompete those species which it is forced to live in balance with. After such upsets, the intestinal balance can be replenished by administrating beneficial bacteria via the feed. The principle of outcompeting undesirable intestinal bacteria with desirable ones is well known as the probiotic principle.

Probiotics in animal nutrition are live microbial feed supplements which beneficially affect the host animal by improving its intestinal microbial balance (Fuller 1989). The improved intestinal balance results in no diarrhoea or fewer days of diarrhoea. This will result in better average daily weight gain and improved feed conversion, especially around weaning time.

Fig. 1: Effect on daily weight gain of piglets by using a probiotic (BioPlus® 2B), average of 19 trials.

Solutions of natural origin

The selection of bacteria which can assist maintaining intestinal balance is aided bynature. In animals living naturally the intestinal balance is usually not affected by sudden changes in feed, as is often the case in modern animal husbandry. On the other hand the continuous and balanced supply of bacteria — beneficial or less beneficial — is secured from natural sources, mainly from the soil. Under the conditions of modern animal husbandry the bacterial population in the intestines of the pig is under continuous pressure from potential pathogens and a balanced supply of bacteria is not readily available.

Feedstuffs are designed to ensure fastest possible growth in the shortest possible period of time. The highly concentrated nutrients, however, might favour the upset of the intestinal balance. This balance can be controlled by the intake of beneficial bacteria, though the number of these is usually lower in the modern rearing facilities than in the natural environment. Heat treatment and/or pelletising means that the feed itself does not contain a naturally balanced bacterial population. Theoretically, supplying the animal with probiotic bacteria, which can outcompete pathogens, will help to reestablish the intestinal balance and, thereby, increase the profitability of pig production.


Since the search for feed additives that could replace antibiotic growth promoters has become more intensive, probiotics have gained more attention. The effect of beneficial bacteria on humans, hypothesised first by Metchnikoff, is well known. The use of probiotics in human nutrition aims to maintain intestinal balance and the side effect of reaching this goal, better nutrient utilisation, is only of importance to animal husbandry. Since the start of the search for probiotic bacteria, which can be used as feed additives, attention has mainly focused on lactic acid bacteria.

Lactic acid bacteria are natural inhabitants of the pig’s intestines and are generally known for their beneficial effects in maintaining the intestinal microbial balance. Lactic acid bacteria, however, are sensitive to modern feed processing, particularly heat treatment, for instance during pelletising. Therefore, special treatments are needed in order to ensure they survive heat treatment and stay viable on reaching the intestines.

Survive pelletising

Surviving modern feed processing is a major requirement of any probiotic. The protection of live lactic acid bacteria against heat treatment, however, is not without difficulties. The search for natural solutions in order to obtain in-creased stability in the feedstuff, has led to the evolution of naturally spore forming bacteria. Spores are provided with the best possible protection against heat and moisture: the spore wall. The bacterial spore form is highly protected and only becomes an active form when the environmental conditions are optimal.

Feed conversion

The probiotic principle might fit the new ‘green’ requirements of customers preferring natural solutions. Nevertheless, modern animal husbandry, organic or not, needs to be profitable as well. No farmer will use ‘green’ or ‘not green’ additives that do not improve their bottom line. The question they ask is ‘can a probiotic feed additive improve feed conversion?’ and, if so, ‘how?’

Originally the probiotic idea explained the improved intestinal balance in humans — feed conversion and daily weight gain were not terms that could be used in the context of human health. However, since the 1980s it is widely acknowledged that improved intestinal balance by animals, not only results in lower mortality but also in improved weight gain and feed conversion. International studies on probiotics and feed conversion show that in pigs up to four months of age feed conversion can be significantly improved by administrating probiotics in the feed.

Results of controlled trials show that piglets with balanced intestinal flora, as a result of the use of heat stable probiotics, need 5-10% less feed for 1kg weight gain (see Figs. 1 and 2).

Fig. 2: Improved feed conversion of piglets by using a probiotic (BioPlus® 2B).

Digestibility and bacterial growth

Several bacillus species showed beneficial effects on the intestinal balance and improved feed utilisation and weight gain. This positive effect is due not only to competitive exclusion, by outcompeting undesirable bacteria from specific sections of intestinal ecosystem, but by affecting nutrient metabolism as well. Several bacillus species, for example B. subtilis, are known and have been used for their extensive enzyme production. In the intestinal content this means that there are less nutrients undigested and, therefore, less available for growth of undesirable bacteria.

The more undigested nutrients there are in the intestines, the more likely that maldigestion, not physiological degradation of nutrients, will occur. This means a loss of nutrients and thereby a waste of feed and a lower weight gain. Better digestibility means there is a lower density of nutrients in the manure and this leads to less optimal conditions for growth of undesirable bacteria in the immediate environment of the animals. This is of particular importance for sows and newborn piglets as newborn piglets have a sterile gastrointestinal tract, which will be colonised by bacteria from their surroundings.

It is very important that the bacterial population is not dominated by potential pathogens. High digestibility will, therefore, not only ensure better growth, but lower the pathogen pressure on the piglets.

Hygiene control

In modern pig production high hygienic standards reduce the number of pathogens and potential pathogens in the rearing environment. At the same time the natural bacterial population is also significantly decreased, so can not always outcompete undesirable bacteria in the pigs’ environment or in their intestinal tract. Disinfection methods cannot be aimed only at the undesirable bacterial populations! By administrating beneficial bacteria through the feedstuff the microbial balance in the gastrointestinal tract and in the manure can be replenished in a way that the beneficial bacterial population dominates or overcomes undesirable bacteria.

Solution invented by nature

Even sceptics admit that pig nutrition of today is far away from that of the old days when the only source for microbially balanced feed was nature. Extensively kept pigs had the opportunity to consume a lot of different foods. This not only resulted in a balanced nutrient intake but, since the contaminated soil could not be avoided, the continuous intake of bacteria which could outcompete undesirable bacteria also occurred. Modern pig nutrition has the opportunity to administer probiotics with proven effects in order to establish an intestinal bacterial population, which bestows the benefits of natural extensive pig production.

Fig. 3: Improved nutrient digestibility in piglets, between the age of 21-56 days.

Source: Chr. Hansen - March 2006
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