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Do probiotics work for poultry?

Probiotics might be one of the solutions to reduce the effects of the recent ban on antimicrobial growth Promoters (AGPS) in feed. However, the mode of action of Probiotics is still not fully understood and evaluating Probiotics in an objective way is therefore essential. In this article, Loek de Lange explains how the microflora in chickens is being developed, how Probiotics can influence this and, in return, have its effect on feed efficiency.

by Loek de Lange

Probiotics are used to influence the microbial flora in the gut and are usually defined as live microbial feed supplements that have a beneficial effect on the host animal by improving its intestinal microbial balance (Fuller, 1989). However, this definition does not clarify how probiotics may be beneficial to the host animal. Is it about improvement of health? But, how do we define health? Are probiotics meant to reduce pathogens and subsequently improve the bacterial quality of the carcass after slaughter, or is it about improving the utilisation of feed? Also, how probiotics may effect the intestinal microbial balance is not described in the definition stated by Fuller.

Intestinal microflora

The diversity and succession of the microbial flora in the ileum and ceaca of the maturing broiler chicken is well described by Lu (2003) after analysing the 16S ribosomal RNA gene sequences. Nearly 70% of the sequences from the ileum are related to those of the Gram-positive Lactobacilli, while in the ceaca, 65% is related to Clostridiaceae. During the first 14 days of age, the ceacal microflora is a subset of the ileal microflora. As the bird matures each region develops its own unique bacterial community. At a young age, L. acidophilus is abundant in the ileum and shifts to L. crispatus at a later age. In the ceaca there is a shift from Clostridia to Eubacterium and Fusobacterium species as the birds mature. All these species are Gram-positive and sensitive to many AGPs that are now banned in the EU. The unique microbial community at a very young age suggests that the early bacterial community is relatively transient and is replaced by a more stable community later in life. This suggests that influencing the bacterial community by probiotics or feed is probably most successful at a very young age in the proximal part of the gastro intestinal tract.

Adverse effects of the microbial flora

Competition for nutrients by intestinal bacteria also exists between host and commensal flora. The word commensal literally means 'together at the table'. Part of the protein and carbohydrates are already consumed by bacteria in the crop and fermented mainly to volatile fatty acids (VFA) and bacterial protein. Although the end products from this fermentation are utilised by the host, the indirect digestion is less efficient and decreases the utilisation of the feed. So, the more intensive this fermentation is, the lower the utilisation of the feed becomes. The pH or concentration of VFA is often used as an indicator for quantifying this fermentation. Another phenomenon is the deconjugation of bile salts by the microbial flora. An increase in microbial activity in the intestine is associated with a deconjugation and loss of bile salts resulting in a low digestion of fat, particularly long saturated fatty acids, together with a rather poor feed conversion (Langhout, 1998). Another adverse effect of the microbial flora is the degradation of glycoproteins in the mucus and the diminished activity of brush border enzymes (Dijk, 2002). An advantage, which can also become a disadvantage, is the effect that bacteria have on the immune system. Cell wall components and the DNA of Gram-negative and Gram-positive bacteria stimulate the immune system. This can cause a lower feed intake, an increased production of white blood cells and the formation of acute phase proteins in liver and blood, together with heat shock proteins in the cells. The extra protein required for this formation originates mostly from muscle proteins. This means that the metabolism of the animal becomes catabolic. This will decrease the daily gain of the animal and increase the loss of protein and essential amino acids (tryptophan).

Probiotics may improve health

A healthy intestinal microflora is important to prevent chickens from being infected with external pathogens. The commensal bacteria stimulate the development of the immune system of the host and compete for nutrients and attachment sites with pathogenic bacteria (competitive exclusion). In addition, there is also a direct interaction and communication between bacteria via molecules (quorum sensing or cross-talk). These are the ideas behind the development of probiotics. The older probiotics were mainly based on one lactic acid producing species as Lactobacilli and Bifido's; the newer ones are often multispecies and also contain Bacilli, Streptococci and Clostridiaceae. The main objective of these new probiotics is to keep out pathogens and to improve intestinal health and bacterial carcass quality.

Improving FE with Probiotics doubtful

Decades of research with probiotics have not led to a massive use of these products in animal feeds. A renewed interest for probiotics has resulted from the ban on AGPs in the EU in 2006. Replacing ANTI-biotics, which suppress growth of a large part of the commensal microflora and improve the FCR, with PRO-biotics, which stimulate the growth of certain bacterial strains, seems to be more than a "contradictio in terminis". To achieve a good feed efficiency (FE) a sound balance between the host and its microbes is important, meaning that the number of commensal bacteria should be kept quite low. That is, to my opinion, the main effect of the classic AGPs, although other direct effects of AGPs on the metabolism of the host (suppression of inflammatory effects) might also be an explanation for the effectiveness of these products. A good indicator in the microbial flora for a good utilisation of the feed seems to be the relative quantity of DNA from Lactobacillus acidophilus (LA). In feeding trials in broilers by De Heus Feeds, where the growth of the intestinal flora to test alternatives for AGPs was stimulated, a shift within the bacterial community in the gut was frequently observed. It was shown that LA becomes more dominant when the fermentation is stimulated and the numbers of LA go down when AGPs or other antibacterial components are added to the feed. When the relative quantity of the 16S ribosomal RNA genes for LA in the total bacterial mass increased, the feed conversion ratio becomes worse. This clearly indicates that high numbers of LA in the gut are related to bad feed efficiency.


A good balance between the host and the microbes in the gut, together with a good balance within the microbial intestinal community, is essential for a healthy and economical production of broiler chickens. A clear indicator to understand this principle might be the relative quantity of bacterial DNA originating from LA. It is unlikely that the addition of probiotics (under normal practical conditions) has a positive effect on the feed efficiency and the economics of fattening broiler chickens.

About the author:

Loek de Lange graduated in animal husbandry from wageningen university in the netherlands in 1980. he then went on to work work as a nutritionist at several feed companies in the netherlands, responsible for feed formulation, research & development, quality assurance and extension. since 1998, de lange has been the r&d manager at de heus/ koudijs feeds, specialising in animal nutrition and intestinal health. since 1999, he became a member of the advisory research committee of the dutch product board for animal feeds. Contact info: llange@de-heus.nl  

Source: Feed Mix magazine Volume 15 nr.1

Editor AllAboutFeed

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