Young broiler chickens© Design Pics Inc/Rex/Shutterstock

The impressive genetic improvement of poultry growth rate has led to a modern bird with a very low feed conversion, high average daily gain and low mortality.

This improvement in growth and the corresponding feed conversion ratios put enormous pressure on the digestive system of the birds from the very first day of life.

Any factors that result even in the slightest reduction in digestion and absorption may enhance the development of enteric disease in an intensively kept commercial broiler.

See also: Why it’s vital to pick the right fibre for poultry diets

Among influencing factors, coccidiosis is considered to be the most important one, as any infection of coccidia requires an invasion and finally destruction of the host cells to fulfil the reproduction cycle of the parasite.

Very often coccidiosis infection is directly linked with digestive problems such as bacterial enteritis (disbalance of bacterial microflora) or even necrotic enteritis in case of presence of Clostridium perfringens.

The microbiome

In the past, the investigation of intestinal bacterial population has been done with in vitro culture techniques. These techniques are able to assess only those bacterial species that can be grown in different media in laboratory conditions.

More recently, modern approaches using molecular techniques have been able to show that a significant part of intestinal microbiota has never been cultured. So only a small fraction of intestinal bacterial population has been studied.

Any conclusions regarding the composition of intestinal microbiota and its functions must be drawn very carefully.

Today there is a better understanding of the role of microbiota in oral tolerance and physiological functions of a healthy gut, and this has helped to disqualify simplistic views such as the idea of “good” Lactobacillus spp and “bad” Clostridium spp bacteria.

Nowadays, microbiota is considered as a gene toolbox that is complementing the gene pool of the host.

Research is focusing on unraveling the complex interactions of what kind of gene pool is linked with good gut health and understanding how genes, both from the gut and its microbiota, can be switched on and off with different diet types, in order to reach the best performance: lowest level of inflammation, best digestive and absorptive properties.

What we know so far is that a composition of intestinal microbiota is changing throughout the life cycle of a bird, becoming quantitatively and qualitatively more complex with the age.

Environmental factors

In addition, environmental factors, such as stocking density, diet composition and feeding practice, management, housing conditions, pathogen load in the environment, and use of antibiotics can modify intestinal microbiota.

Feed withdrawal, especially over a longer time, causes a reduction in the number of detected bacterial species. Also, from one segment of the gastro-intestinal tract to the other, bacterial populations of the gut vary significantly.

In the small intestine of a healthy bird, Lactobacillaceae spp are dominant, whereas in the caeca Clostridiaceae spp prevails, which is connected with different pH and physiologic functions of these intestinal segments.

There are some members of mucosa-associated microbial community that are considered to be especially crucial for a healthy status of the gut. These are bacteria producing short chain fatty acids, like acetic, propionic and butyric acid, during the fermentation process of dietary carbohydrates.

Production of butyrate near the epithelial cells and in close association with invading and histotoxic pathogens promotes development and recovery of the villi, stimulates the expression of the tight junction proteins, limits invasion of pathogens such as E coli and Salmonella and further promotes a beneficial microbial ecosystem, which leads to an overall increase in tissue health.

On the contrary, mucin-desulphating bacteria and sulphate reducers create hydrogen sulfide, which enhances some pathogens and causes tissue damage.

The main negative gut health drivers are:

  • Parasites (coccidiosis)
  • Viral
  • Bacterial
  • Anti-nutritional feed compounds (Mycotoxins, NSP’s)
  • Feed-poor management and poor physical feed texture

 

 

 

 

 

Antimicrobial alternatives

Pressure on the use of therapeutic antimicrobials has caused a scramble to find alternative solutions to develop a healthy digestive system in poultry.

Different natural and nontoxic alternatives for antibiotics, such as prebiotics, probiotics, phytotherapeutics (botanical products – herbs and etheric oils), organic acids and enzymes have been investigated for their improvement of intestinal health and animal performance in general.

Also, bacteriophages, antimicrobial peptides and toll-like receptor agonists are under investigation.

Each alternative has a different mode of action and its own specific features – it will depend on different contributing factors as to which product will be most cost effective when it comes to improving intestinal health in different situations.

Prebiotics are defined as non-digestive food ingredients that selectively favour the multiplication or metabolic activity of a specific fraction of microbiota in colon. Inulin and oligofructose/fructo-oligosaccharides are from plant roots and mannan-oligosaccharides and B-glucans from yeasts.

They stimulate bacteria that are naturally present in the intestine, selectively increasing beneficial ones and decreasing non-desirable ones. For B-glucans an immunomodulatory effect next to prebiotic action has been shown. MOS inhibit bacterial binding to the villi and support Lactobacillus spp.

Probiotics are single or mixed cultures of living micro-organisms, which beneficially affect the host by improving the properties of the indigenous microbiota.

The mode of action of probiotics is a competition with pathogens for adhesion site and for nutrients, immunomodulation and production of antimicrobial compounds.

They are also known to regulate intestinal microbial homeostasis and stabilise the gastro-intestinal barrier functions. A more diverse bacterial population is beneficial over a single dominate bacterial species, as is seen in the more stable adult gut microbiome.

Organic acids are molecules that are widely present in nature. They occur in different plants and animal tissues or originate from intestinal bacterial fermentation of plant materials such as fibres, starches and sugar.

The primary antimicrobial action of the organic acid in the feed or drinking water (in vitro) is through lowering of the pH, the reduction of buffering capacity of the feed and a direct effect on the microbial population.

Much more important is the mode of action of organic acid in the digestive tract of the animal. In the bacterial cell the acid will dissociate, which will lead to the suppression of the cell enzymes and depletion of energy as bacteria will try to maintain a neutral pH of the cytoplasm pumping protons out of the cell.

Botanical products

Essential oils and herbs contain phenolic compounds, glycosides and alkaloides such as thymol (thyme), carvacrol (oregano), allicin (garlic), cinnamaldehyde (cinnamon) and other active chemical substances.

Some of them have antimicrobial, anti-inflammatory, mycotoxin binding, antiparasitic, anti-oxidant or immunomodulation properties. T

hey also positively influence tight junctions, stimulate the endogenous digestive enzyme and stimulate the appetite.

When using essential oils and herbs, it is important to keep in mind that these products show large variation in composition, depending on origin, harvest and storage and extraction methods.

Alternative products, depending on the type, can act on different levels on intestinal health: they can improve gut developmental physiology, modulate immune response of GALT (gut-associated lymphoid tissue), reduce oxidative stress, improve digestibility. They work not only against bacteria but mostly also have other additional features that beneficially support gut health.

They have a big potential as an alternative to a classical antibiotic treatment of enteric diseases.

*The above reports were written by Andrew Walker, of Slate Hall Veterinary Services