Do probiotics work for poultry?

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.

Conclusions

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