The use of probiotics, prebiotics and synbiotics in animal nutrition is substantially growing. On the one hand, this is the result of the increased restriction to the use of antimicrobial growth promoters. On the other hand, there is an interest in improving animal welfare and in reducing the risk of pathogens entering the food chain and affecting the final consumers. This article introduces the topic, which is further developed in other articles specific to each species.
Nowadays, the goal of animal production is to provide quality and safe food for human consumption, prioritizing animal welfare, respect for the environment and consumer safety.
It is well known that the risk of contamination by pathogens, such as Salmonella and Campylobacter, in animal products has been and still is a major concern for the European health authorities. This originated a legislative framework of great impact on the operational efficiency of the livestock sector.
The concerns surrounding the development of antibiotic resistance by some pathogens and the possible transfer of the genes responsible for resistance from the animals to the human microbiome led to the ban of antibiotic growth promoters in the European Union, in 2006. Currently, this concern is being the cause of legislative initiatives that establish a significant reduction in the therapeutic use of antimicrobial drugs in food-producing animals.
Given this scenario, there is a real need for viable solutions that stimulate animal growth and, at the same time, reinforce the animal’s own defence mechanisms. This is necessary to control infections by pathogens that may pose a risk for animal and consumer health.
One possible measure is the use of feed additives. They positively affect the performance and welfare of the animals, particularly through the modulation of intestinal microflora, which plays a key role on the maintenance of animal health.
A balanced intestinal microflora constitutes an effective barrier against pathogen colonization, produces beneficial metabolic substrates (such as vitamins, bacteriocins and short chain fatty acids), and stimulates the immune system, without causing inflammatory processes. In this context, probiotics, prebiotics, and synbiotics are tools we should take into serious consideration.
The main effects of these types of feed additives include an increased resistance to colonization by pathogenic bacteria, and a reinforced immune response of the intestinal mucosa. This results in a lower pathogen load in the farm environment, better health status of the animals, and a reduced risk of pathogen transmission to end consumers through the food chain.
In this article, we will discuss the concepts of probiotic, prebiotic and synbiotic, besides reviewing some research on their application in swine, poultry and ruminants.
Probiotics started to be used in animal diets in the 1970s. Parker (1974) used the term “probiotic” for the first time in the animal production sector. Since then, several definitions have been proposed for the term “probiotic”, being the one given by FAO/WHO (2002) the most widely accepted:
“probiotics are live microorganisms, which when administered in adequate amounts, confer a health benefit to the host”.
It is important to point out the meaning of this definition: for a microorganism to be considered as a probiotic it must have a positive effect on animal or human health.
According to FAO and WHO, probiotics have a beneficial effect on the health of the host.
Figure 1. Uses and effect of prebiotics, probiotics and synbiotics,
Mode of action of probiotics
According to Blanch (2005), the different mode of action of probiotics are:
Figure 2. Mechanisms of action of different probiotics.
The current European legislation warns that the main genera to which probiotics registered in the EU for use in animal diets belong are Bacillus, Lactobacillus, Enterococcus, Bifidobacterium, Clostridium (bacteria) and Saccharomyces (yeast).
Prebiotics are defined as “non-digestible food ingredients that have a beneficial effect on the host, selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon” (Gibson and Roberfroid, 1995). For a substance to be classified as a prebiotic, it is required to meet at least three criteria shown in Figure 3.
Prebiotics are “non-digestible food ingredients that have a beneficial effect on the host, selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon”
Figure 3. Criteria to be followed by prebiotics (after Scantleburry-Manning and Gibson, 2004).
Table 1. Comparison between effects of prebiotics on small and large intestine (adapted from Gaggia et al., 2010)
Most prebiotics currently used in animal nutrition are carbohydrates and oligosaccharides with different molecular structures.
The most promising prebiotics are the non-digestible oligosaccharides such as fructooligosaccharides (FOS, oligofructose and inulin), galactooligosaccharides (GOS), trans-galactooligosaccharides (TOS) and lactulose. Although on certain occasions they are referred to as “prebiotics”, the mannanoligosaccharides (MOS) do not selectively favour the populations of beneficial bacteria; therefore, they cannot be considered as prebiotics in the strict sense of the term. Researches on MOS mechanism of action indicate that these compounds bind to mannose-binding lectins of Gram-negative pathogens such as Salmonella and E. coli, dragging them through the intestine until their excretion via feces (Baurhoo et al., 2007).
Synbiotics were defined in the 1990s by Gibson and Roberfroid (1995) as “mixtures of probiotics and prebiotics that beneficially affect the host by improving the survival and implantation of live microbial dietary supplements in the gastrointestinal tract”. The study of the efficacy of synbiotics used as feed additives has been the subject of further investigations. Currently, there are symbiotic products in the market, registered as additives for use in animal nutrition.
New holistic strateegies strategies are being developed. They aim is to improve the performance and welfare of the animals, as well as reduce the presence of pathogens in livestock farms. This is particularly true considering the future legislative framework regarding animal health and nutrition.
One of these strategies involve the manipulation of the gastrointestinal microbiota through the administration of probiotics, prebiotics or synbiotics. The final objective is to obtain a better intestinal health, due to microbial diversity, microbial stability, presence of metabolites, and interactions with the enteric epithelium and the immune system.
Besides the therapeutic approach, this type of additive can be used to prevent the occurrence of gastrointestinal infections. They act not just on the pathogens (like antibiotics), but also on the modulation of the gastrointestinal environment, reducing the risk of gastrointestinal diseases in synergy with the immune system of the host.
This article was originally published on nutriNews Spain, under the title Prebióticos, Probióticos & Simbióticos en nutrición animal
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