E.coli naturally resides in the gut of many animals, including humans and poultry. However, the more animals in close proximity, the higher the levels of E.coli in the environment, which then becomes the source of the infection from bird to bird.
E.coli, salmonella and campylobacter are spread from bird to bird through the litter. Left unchecked will survive in the bedding for long periods.
In addition, when an animal's immune system is compromised, they are more susceptible to infections. In mild cases, this will diminish FCR performance, or more severe cases can lead to health problems for the animals requiring antibiotics.
Therefore, it is essential to maintain a good environmental microme in the building throughout the crop and high hygiene practices on the farm.