Shining a light on gut health

By Prof Dr Peter Spring , College of Agriculture, Forestry and Food Science (HAFL), Zollikofen, Switzerland

The digestive system plays a key role in both supplying nutrients to the animal and in nutrient utilisation. Only with a healthy digestive tract can the bird reach its genetic potential. While being the supplier of nutrients to all other organs, the digestive system itself is also one of the major users of nutrients, as it has a high maintenance requirement. If the digestive system is challenged, its requirement for energy and protein increase sharply.

This drastically reduces the nutrients which are available to the bird for growth and thus weight gain, resulting in a reduction in feed efficiency. In addition, most intestinal challenges will lead to a reduction in feed intake, which will further compromise bird performance. The reach of intestinal health goes far beyond production efficiency as it also plays key roles in minimising environmental impact and in protecting animal welfare and product quality. Poor intestinal health increases the moisture content of the excreta and will therefore negatively affect litter conditions. E

xcessive litter moisture leads to elevated ammonia emissions. Producers in many countries will have to reduce ammonia emissions in the coming years in order to reach the targets governments have agreed to, by signing the Göteborg protocol. Excessive litter moisture has also been shown to increase footpad dermatitis, hock burns, processing downgrades and condemnations. Control of both foot pad lesions and litter conditions are part of the EU welfare regulations.

Nutrient availability to microflora

Antibiotics still play an important role in protecting gut health in poultry production. A proportion of global poultry production still uses antibiotic growth promoters and many countries that have banned them rely too heavily on veterinary prescribed antibiotic treatments. Whether used as growth promoters or to treat infection, the global poultry industry must drastically reduce the use of antibiotics in the coming years, without putting intestinal health at risk. This will require further optimisation in biosecurity, management and nutrition in both breeder and production flocks. The diet should support the bird by quickly establishing a stable microflora.

In order to strive for microflora stability it may become necessary in the future to keep formulation restrictions more narrow, in order to reduce the variation in inclusion level of ingredients. In a time of high fluctuations in ingredient costs, narrow restrictions will, under certain conditions, lead to slightly higher diet costs. However, if a stable microflora can be established and maintained, the bird will return this extra cost with better performance. In the absence of antibiotics, the most efficient way to influence the gut microflora is via control of the nutrient availability and flow to those microbes. The key nutrients to consider are protein, energy (starch, fat) and dietary fibre. In addition, stringent measures should be taken to minimise the presence and impact of dietary contaminants such as mycotoxins, which negatively impact gut health and performance.

Focus on protein digestibility

Protein and amino acids should be formulated based on digestible values in order to maximise protein digestibility and to keep the total protein concentration reasonably low. The flow of too much undigested protein to the lower gut will alter the gut environment and can favour the proliferation of Clostridia perfringens. High protein concentrations will also lead to increased uric acid in the excreta, which is known to be linked to higher litter moisture.

A challenging issue is to provide starch in the right form to the bird. Both overall digestibility and its rate of digestion have been shown to influence microfloral composition. Particularly when feeding wheat, starch digestibility can be too fast and thus favour the growth of C. perfringens. Toxins produced by C. perfringensare responsible for necrotic enteritis (NE). Starch properties in the digestive tract are mainly affected by ingredient, particle size and heat processing. Therefore, changes in diet composition might also demand adaptations in the milling process. Several studies have shown that whole wheat feeding may contribute to improved gut performance. In order to manage these aspects of diet formulation, the ingredient matrix should take starch properties into consideration.

Further dietary factors

Consideration should also be given to the fat quality and the use of an appropriate enzyme cocktail ideally matching the major raw ingredients used in the diet. Particularly in starter diets, unsaturated fat with a high digestibility should be used. When properly matched, the enzyme cocktail will increase diet digestibility and improve litter quality. Addressing the challenge by increasing dietary zinc or copper is not a solution, as this approach will lead to high levels of those minerals in the litter.

Instead of increasing the level of trace minerals, highly available organic forms should be considered and excessive safety margins should be avoided. In particular, copper and zinc are continually on the radar of regulatory bodies and the industry should respond proactively. Instead of considering ideas of the past, such as high copper or zinc levels, the industry must adopt the latest technologies in the area of feed additives.

Natural carbohydrate fraction

Most recently, new and interesting data have become available on a natural carbohydrate fraction (Actigen, Alltech Inc.) isolated from a specific strain of yeast. It has been shown to support the first line of an animal’s defences, stimulate innate immunity, maintain intestinal function and maximise nutrient absorption. With nutrigenomics, it has been proven convincingly that this natural carbohydrate fraction has unique properties to alter the function of the digestive system and the metabolism of the animal. Nutrigenomics enables the detection and measurement of the change in expression of several thousand genes in the bird all at the same time, in response to a feed product or diet, thus allowing a far more comprehensive understanding of how a concept affects the metabolism and health of the bird.

Among the many changes in gene expression observed, Actigen regulated intestinal enzyme production, reduced cell cycling and heat shock protein production when tested in a challenge model with increased intestinal viscosity. The overall data from this study indicated improved intestinal health and reduced stress. The data also showed that vast differences exist among different yeast products. Dr Hooge recently analysed the existing published broiler performance trials using Actigen and calculated, compared to a negative control diet, 129g higher body weight, 4.5 points improvement in feed conversion ratio and 0.76% reduced mortality. As mentioned earlier, necrotic enteritis is a major reason for the excessive use of antibiotics in commercial production. In a necrotic enteritis challenge model, Actigen was able to alleviate most of the negative effects that the clostridial challenge had on body weight and feed intake (Figure 1).

A small-scale challenge trial using Campylobacter jejuni was recently conducted by Prof Pasmans at Gent University. The addition of the natural carbohydrate fraction to the feed from day one increased the number of viable C. jejuni cells, which were needed to establish colonisation in the caeca of broilers at 16 days of age. According to the researchers, this indicates that the addition of Actigen to the feed at 800 ppm might prevent colonisation of the “first” bird in a flock at limited C. jejuni exposure and thereby prevent flock colonisation. Studies with larger numbers of birds are currently on-going.