From resistance to resilience

Intense genetic selection for improved feed efficiency and intensive production practices have accelerated the progression towards establishing a balance between the efficiencies of immune tolerance and the cost of defence at the gut-and-microbe interface. The intimate relationship and the balance in the gastrointestinal tract between gut flora, host and environment are key to maintaining a healthy gut. Production stresses compromise host resistance and cause an imbalance in gastrointestinal ecology, initiating microbial-mediated disease. Although the inflammatory response is directed at containing disease, it is both costly in terms of feed efficiency and potentially damaging to the cells lining the gastrointestinal tract.

The discovery of gut microfloral involvement in mediating host inflammatory response is revolutionising understanding on the subject. To enhance feed conversion efficiency under current market constraints, the emphasis must shift from maximising host gastrointestinal disease resistance to gut ecology management in order to optimise host resilience. Only a healthy gut can digest and absorb the maximal amount of nutrients to obtain the most out of the diet. If the digestive system is compromised, its requirements for energy and protein increase sharply. This can severely reduce the nutrients available to the bird for growth, thus slowing weight gain and resulting in reduced feed efficiency. Additionally, most intestinal challenges will lead to reduced feed intake that can further impede bird performance.

Decreased feed efficiency and low weight gain are not the only side effects of gut health challenges. Poor intestinal health will increase the moisture content of the excreta, therefore negatively affecting litter conditions. This can augment the level of ammonia in the house and lead to more respiratory problems. Wet litter has been shown to increase footpad dermatitis, hock burns, processing downgrades and more problems. Uneven flocks, runting and stunting, ruffled feathers and an increased chance of mortality can occur as well.

Maintaining gut health

To establish an effective gut health programme, it is important to focus on optimising gut absorptive membrane development and integrity. The early establishment and maintenance of a beneficial intestinal flora is key, since the gut flora competes with pathogens such as Clostridium spp. Furthermore, a favourable flora also helps to stimulate early enterocyte development. The aim of any gut health programme is to protect flock health by establishing and maintaining a stable, normal flora immediately after hatching. This would require several possible interventions:

• Seed the gut with a host-adapted favourable flora, which will prevent the establishment of pathogens. Success is dependent on the degree of challenge.

• Prepare a favourable gastrointestinal environment to help the rapid establishment of the favourable flora. This assists enterocyte development, accelerating gut maturation to assist digestion efficiency and absorption capacity.

• Exclude pathogens to maintain the stability of the gut flora by managing it to ensure competitive exclusion, by preventing the pathogens from establishing and by preventing the negative impact of mycotoxicosis on the gut flora.

• Improve digestion and absorption by reducing substrate accumulation in the lower gastrointestinal tract, thus avoiding negative impacts on the gut flora profile. This will help to improve membrane integrity and therefore improve absorption.

Based on the above multiple-intervention strategy, a unique gut health programme has been developed by Dr S.R. Collett at the University of Georgia. His approach has been shown to achieve improved growth rates and feed conversions by ensuring gut health. The programme advocated by Collett is comprised of the sequence of ‘Seeding’ the gut with beneficial intestinal organisms, ‘Feeding’ these intestinal flora by creating a positive gut environment to allow their proliferation and ‘Weeding’ which involves the selective exclusion of potentially deleterious flora using prebiotics that inhibit pathogens.

Introducing favourable flora

Seeding starts from the parent stock. Since normal eggs have a sterile surface prior to oviposition, the point of lay is the first opportunity for contamination. The level of contamination varies from 103–105 colony forming units (cfu) per egg under clean conditions to 107–108 cfu per egg under dirty conditions, therefore confirming that contamination is a function of the environment into which the egg is laid.

These eggshell contaminants provide the first seed stock for the chick and its gut colonisation at hatch. Positive manipulation of parent stock flora provides the first opportunity for seeding beneficial flora in the gut of the broiler chick. Fernandez et al., 2001, reported that feeding the parent stock mannan-rich fraction (MRF) positively altered the normal flora, significantly enhancing the chick’s resistance to pathogen colonisation. The need for appropriate environmental management of houses, especially management of ventilation, which influences litter quality, is the key for overall success.

Direct-fed microbial preparation at a day old in the hatchery establishes favourable flora prior to the chicks being housed. Hofacre reported that using a direct-fed microbial (All-Lac, Alltech) resulted in improved conditions due to the colonisation of the gut with favourable microbials. He went on to suggest that the direct-fed microbials may be strain-specific, since Lactobacillus acidophilus and Streptococcus faecium were the primary organisms used.

Again, appropriate environmental management of houses, especially of ventilation (which will influence litter conditions, which will in turn intensify any coccidiosis challenge as well as shifting the balance in favour of pathogen populations, impacting the overall gut health of the broiler) is critical. Controlling relative humidity, particularly during the brooding period (when ventilation needs are low), is essential to prevent a proliferation of Clostridium, coccidia and other pathogenic organisms.

Figure 1 – Effect of water acidification in broiler performance (% relative to control).

Creating a favourable environment

‘Feeding’ refers to using preparations consisting of organic acidifiers that reduce pH levels and promote beneficial bacteria. With a beneficial microfloral community and an intestinal ecology established, the resultant healthy villi allow maximum-capacity absorption within the GI tract. Figure 1 shows an overall improvement in broiler performance due to acidification of drinking water.

Selective exclusion of pathogens

‘Weeding’ is the selective exclusion of pathogens by blocking their attachment to the intestinal epithelium. For most bacteria to colonise the gastrointestinal tract, they first need to attach to the epithelial surface. They do this via carbohydrate projections such as lectins, which recognise certain epithelial surface sugars. Many enteric pathogens attach to these sugars via Type 1 fimbria, which recognise mannose. MRF, a second-generation concentrated mannan oligosaccharide (MOS), blocks potential pathogen attachment on the epithelial surface, hence preventing pathogen colonisation and maintaining a stable gut flora.

The improvement in the absorptive capacity of the gut is reflected by the significantly increased body weight gains observed in diets supplemented with MRF compared to control. However, no effects of supplementation on feed conversion ratio (FCR) were observed. This study indicates that there may be a positive dose-dependent response to MRF when looking at the villus-to-crypt ratio, with the decrease at the higher inclusion being caused by over-supplementation.

Figure 2 – Villous surface area.

Continuous process

The Seed, Feed and Weed concept is a continuous process throughout the life of the bird, offering the poultry industry a tool that is safe, natural and effective in ensuring gut health with overall improved performance and therefore cost-effectiveness. This multiple-intervention strategy is likely to be more effective than any single solution often advocated at the farm level.

*All-Lac is not available within the European Union.

References available upon request.