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Why Competitive Exclusion is a critical pillar for integrators
Competitive exclusion (CE) is the biological phenomenon whereby a normal, healthy intestinal microbiota establishes itself within the digestive tract, naturally outcompeting transient, unfavourable bacteria for space and resources.
The evolution of a proven concept
In the 1950s and 60s, as intensive chicken rearing practices expanded, researchers began investigating preventative approaches to support food-chain safety and bird hygiene.
Early studies observed that as poultry mature, they naturally develop a stronger, more robust resistance to undesirable bacterial colonisation in the gut. This led to a breakthrough realisation: the physiological maturation and complexity of the intestinal microbiota is the primary driver behind this natural stability.
Managing the hatchery gap in modern rearing
In a natural environment, a newly hatched chicks’ digestive tract is nearly sterile and early microbiota establishment is predominantly shaped by the hatchery environment.
A first immature microbiota, up to 3 to 4 days old, is characterized by low microbial richness, and is heavily influenced by facultative anaerobes or aero-tolerant species for hatchery and farm environments (Ballou et al., 2016; Ocejo et al., 2019). This mainly contains Proteobacteria represented by the family Enterobacteriaceae (which includes Salmonella and E. coli) and to a lower extent Firmicutes represented by the family Ruminococcaceae (Clostridia, a major butyrate producer) and Enterococcus. A stable level of Lactobacillus is not reached until day 7 – 10, an adult-type adaptive microbiota is acquired at around 20 days old, and intestinal microbial maturation appears to be reached after 40 days old (Lallemand Internal data; Gao et al ., 2017).
This delay in development and a highly variable microbial composition in chicks led to the development of the Competitive Exclusion concept. Initially, researchers introduced the diluted intestinal content of mature, free-range hens to newly hatched chicks, observing a significant acceleration in natural gut stability and resilience. The Finnish microbiologist Professor E.V. Nurmi defined this concept in Nature in 1973, and in 1974, M. Rantala demonstrated that this protective effect was directly linked to the presence of viable anaerobic bacteria.
A precision tool for early gut hygiene
The science has come a long way since the 1970s.
Today, modern CE production utilises commercial microbial cultures (for example AVIGUARD) developed via the industrial propagation of a specific poultry gut seed microbiota under strictly controlled, standardised conditions. While initially conceptualised to support gut health in young broilers, the application of comprehensive viable cultures has proven highly effective across a range of avian species (including turkeys, pheasants, and quails) in establishing the gut environment and supporting its resilience against a broad spectrum of transient pathogens and diseases.
The 5 core mechanisms of Competitive Exclusion
Competitive exclusion does not rely on a single mode of action. Instead, it supports the bird’s digestive efficiency and natural defences through five overlapping, ecological pathways:
| Mechanism | How it protects birds |
| Environmental Competition | Established beneficial bacteria maintain a favourable, balanced pH environment that is naturally inhospitable to transient organisms. |
| Nutrient Depletion | A dense, mature microbiota rapidly consumes available food sources, leaving fewer nutritional resources for undesirable bacteria. |
| Receptor Blockade | Beneficial bacteria occupy key physical binding sites along the intestinal wall, preventing transient bacteria from attaching. |
| Defensive Priming | Early microbial colonisation naturally conditions and prepares the gastrointestinal tract’s endogenous structural barriers. |
| Physical Biofilm Barrier | A highly stable, robust microbial community forms a natural structural layer that reinforces and protects the intestinal lining. |
Aviguard: Established product, ongoing research
Even though competitive exclusion is over 50 years old, it remains an indispensable strategy for modern poultry systems. Aviguard has been proven in over 70 scientific publications, produced in the UK and used for over 30 years. Ongoing research conducted internally, with customers and presented at global conferences. Over the last 3 years, 8 posters have been presented at European Symposium Poultry Nutrition (ESPN), World Veterinary Poultry Association (WVPA), World Poultry Science Association (WPSA), European Poultry Conference (EPC), International Symposium on Salmonella & Salmonellosis (I3S), and the International Conference on Poultry Intestinal Health. These cover a wide range of topics including Enterococcus, coccidiosis, vaccine compatibility and synergy, immune organ development, zootechnical performance in pullets and broilers.
References
- Ballou, A. L., Ali, R. A., Mendoza, M. A., Ellis, J. C., Hassan, H. M., Croom, W. J., Koci, M. D. 2016. Development of the Chick Microbiome: How Early Exposure Influences Future Microbial Diversity. Frontiers in veterinary science 3:2.
- Gao, P., Ma, C., Sun, Z., Wang, L., Huang, S., Su, X., Xu, J., Zhang, H. 2017. Feed-additive probiotics accelerate yet antibiotics delay intestinal microbiota maturation in broiler chicken. Microbiome 5(1):91.
- Nurmi, E. V., & Rantala, M., 1973. New aspects of Salmonella infection in broiler production. Nature, 241, 210.
- Ocejo, M., Oporto, B., Hurtado, A. 2019. 16S rRNA amplicon sequencing characterization of caecal microbiome composition of broilers and free-range slow-growing chickens throughout their productive lifespan. Scientific reports 9(1):2506.
- Rantala, M., 1974. Cultivation of a bacterial flora able to prevent the colonization of Salmonella infantis in the intestines of broiler chickens, and its use. Acta Pathologica Microbiologica Scandinavica, Section B, 82, 75–80.
Published Feb 10, 2026 | Updated Jul 1, 2026