ARTICLE FEED & ADDITIVE MAGAZINE November 2025 79 the flock through the gut, the respiratory tract, or even the cloaca (Figure 2). Contamination with E. coli does not always lead to colibacillosis. However, the risk of serious disease increases when birds experience a drop in immunity -due to stress, viral infections, mycotoxins in feed, or other factors- combined with a weakened mucosal barrier (e.g., leaky gut, skin lesions, dusty environment, etc.) or excessive environmental pressure (e.g., inadequate sanitation, history of E. coli-related mortality, biosecurity breaches, poor drinking water quality, presence of pests, etc.). Stress triggers the amount of E. coli excreted in birds’ feces, resulting in a higher bacterial load. At the same time, weakened immunity creates favorable conditions for the development of colibacillosis. In modern poultry, which are particularly sensitive, each farming challenge can result in a colibacillosis outbreak within the flock, resulting in reduced performance and, in severe cases, mortality (Figure 3). Mainstream approaches to managing colibacillosis in poultry - vaccines and antibiotics - face growing limitations. Autogenous vaccines require strain-specific formulations, with usually a combination of several valences tailored to the farm, and frequent updates to address emerging new E. coli strains within the flock. This strategy involves high direct costs and requires additional handling when vaccines are administered by injection. Antibiotic treatments typically result in a rapid drop in mortality, but these effects are often shortlived. Once treatment ends, the environment remains heavily contaminated, facilitating recontamination, and a rebound in mortality is often observed within a few days. Furthermore, repeated use of antibiotics promotes bacterial resistance to the active molecules used, limiting future treatment options. The range of available medication has been significantly reduced due to regulatory constraints on the use of colistin and some newer-generation antibiotics. The remaining options Multiplication in digestive tract Multiplication in faeces Diffusion in dust Dust Water Feed E. Coli Figure 2. Vicious Circle of bird recontamination by E. coli: Birds as Reservoirs and Incubators Viral infection Stress Mycotoxins in feed History of mortality due to E.coli Non-optimal fallowing Pododermatitis Cutaneous infections Leaky gut Reduced immunity High pressure E.coli Rupture of the mucosal and/or cutaneous barrier Colibacillosis Biosecurity breach Pests: Reservoirs of pathogens Figure 3. Main Factors Leading to Colibacillosis
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