With increasing pressure to cut the use of antimicrobials, poultry producers are having to look for alternative strategies when it comes to controlling common diseases such as colibacillosis.
This condition is caused by the Gram-negative, rod-shaped bacteria E coli. Those strains causing disease are known as avian pathogenic E coli (APEC). They have developed adaptations enabling them to live outside the intestinal tract, leading to both localised and systemic manifestations of the disease.
This is a widespread problem for the UK poultry industry, resulting in significant economic losses due to morbidity, mortality, reduced production and carcass condemnation.
Keith Warner, director of The Minster Veterinary Practice in Hereford, estimates that E coli is causing problems in around 5% of broiler flocks.
"With chick mortality during the first week of life, E coli is involved in most cases," he says. "The disease can also lead to unevenness, which will persist throughout the life of the flock, making it more difficult to manage and causing issues with uniformity at the processing plant."
But it is still too soon to assess the impact of reduced use of antibiotics for broiler chicks, he says. "Companies are using different approaches. At one end of the spectrum, some have stopped using antibiotics completely - that's probably around 10% of broiler flocks. Most companies have made some reduction and we're working alongside them to achieve the best results."
E coli can be introduced into day-old chicks from the breeder flock or hatchery, or can be picked up from the environment in the chicken house.
Daniel Parker, a partner at Slate Hall veterinary practice near Cambridge, says E coli is the most significant bacterial pathogen found in chicks during their first week, with management and hygiene strategy playing an important role in prevention.
"Breeder flock management, the handling and storage of hatching eggs, the quality of the egg shell and the whole incubation and hatchery process - they can all have an impact on whether E coli becomes established in the chick," he says.
"The majority of day-old chicks will have some E coli, and some strains are inherently more pathogenic than others. But it's important to keep infection to a low level and to establish immunity against the primary pathogens."
Routes to infection
The first stage of infection is when the bacteria attach to epithelial cells of the respiratory, intestinal or other mucosal surfaces of the bird. Many of these bacteria are then able to pass through the defensive layer of mucosa, finding their way into blood vessels where they are able to persist and multiply systemically.
Attachment to target cells is aided by the presence of virulence factors such as adhesins, while colicins help inhibit the growth of other competing bacteria.
Classification of the different strains of APEC has routinely used serology, with Weybridge and the other AHVLA centres playing a key role in monitoring the E coli situation. However, this method is slowly being replaced by genotyping.
Currently, most infections caused by APEC are controlled indirectly by vaccination against primary respiratory and immunosuppressive pathogens, together with either therapeutic and/or metaphylactic use of antimicrobials.
To safeguard the continued availability of these antimicrobials, all those involved need to consider reducing reliance on them and ensuring their responsible use.
An understanding of how they work and move through the body is required to help make the correct choice of antimicrobial, route of administration, dose and duration of treatment. Such use also needs to be carefully monitored.
Together with employing best practices in all aspects of biosecurity and hygiene, this will help to ensure the health and welfare of broiler and layer flocks, while reducing the likelihood of antibiotic resistance.
Stuart Andrews is poultry technical manager of Pfizer for UK and Ireland. The company is soon to launch a new vaccine, Poulvac E coli, designed to reduce mortality and lesions associated with colibacillosis. Recently licensed in the EU, Pfizer believes it will play a significant role in reducing problems with E coli.