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Controlling salmonella infection

Course: Salmonella regulations | Last Updates: 7th October 2015

Dr Rob Davies
Leader of the NRL/OIE Salmonella Reference Laboratory
Biography >>

The Salmonella rules, which apply to pullet rearers and laying flocks producing eggs graded under the Egg Marketing Regulations, have a wide-ranging effect on the poultry industry. Producers have to send off regular samples for Salmonella testing, with flocks that test positive being subject to restrictions that could cause serious financial losses.

Which Salmonella species are being targeted?

Salmonella Enteritidis and S Typhimurium bacteria.

What can I do to prepare for the new regime?

Maintaining a high standard of biosecurity is the best defence. Putting up printed notices explaining procedures, and installing a doorbell system to stop visitors entering the housing are good measures. The owner’s mobile phone number could also be displayed.boot-washing

Footdips, boots and gloves

Position footdips at the farm gate, outside each house and at strategic points like egg stores. Change the solution at least twice a week, using a DEFRA-approved product at the right concentration. A disinfectant "carwash" at the entrance is also useful.

In non-cage housing, supply dedicated rubber boots for each house. Some farms also use colour coding; for example, black boots for outside and green boots for indoor wear. Boot hygiene is especially important if there are other high risk animals such as pigs or cattle on the site.

In caged bird housing, hands transmit disease more readily than feet, so use disposable gloves for tasks like dead bird removal. Ideally, provide a washbasin for each house, an alcohol-based hand cleanser, and disposable towels for drying.foot-dip-sign


Stringent controls should apply to all equipment. One potential disease entry route is via maintenance workers, such as electricians, who may put toolboxes on the floor while working. Studies have shown that faeces collected on equipment are a common method of transmission between units.

A solution is to allocate a cradle, trug or even a clean dustbin liner to each house, to be used for any materials brought in from outside. Washing and disinfecting equipment is also effective, if done properly.

Feed rubber gloves

It is possible for the disease to be brought on to units through feed which has been contaminated by infected faeces.

There is a small risk that S Typhimurium, in particular, can be carried in feed, but this issue is still being debated. Historically, layer feed has not been heat treated to eliminate the bacteria, with the exception of chick crumbs. But heat treatment will increase feed prices and can affect digestion, possibly creating wetter manure that attracts flies and contaminates eggshells.

The potential for adding organic acid and formaldehyde-based feed additives to reduce Salmonella is worth considering. That would increase prices by several pounds a tonne, but might have the added benefit of improving production, by helping to stabilise gut flora.

Rearing stock

It is worth checking to see whether companies you deal with use the same transport cages to bring new stock and take away spent birds. Separate equipment should be used, and vehicles thoroughly disinfected between batches.


Most producers use either an inactivated or live vaccine to give basic protection against Salmonella. But research has shown that up to 20% of chicks may be vaccinated incorrectly. If you have any doubts, you could ask for the vaccination procedure to be audited professionally (see below for contacts). It is important to vaccinate for S.Typhimurium as well as S.Enteritidis in high risk situations such as free-range production or where there are pigs or cattle nearby.

Pest control

Brown-rat-eating-7Rodent control is essential as rodents can act as the main amplifiers of Salmonella on farms, leading to high level of challenge that can overwhelm protection by vaccines. On mixed farms rodents can spread infection from pigs or cattle to poultry. Position baiting points where there is evidence of droppings, urine pillars, grease marks, tracks and chewing. It is best to appoint a trained member of staff to oversee the rodent control plan, which would include drawing up a map of baiting points.

Mini-pit houses offer shelter for rodents, so consider creating baiting ports to deliver bait beneath the slats. Mice can also often be found beneath autonests. If rodents are living in walls and roofs, it may be necessary to remove a portion of cladding and drop bait sachets into inaccessible areas, or ideally create permanent baiting points within wall and roof spaces. Potential entry points into the house such as doors, drains, egg belts and manure should also be baited.

Professional pest control companies will usually visit the unit once every six weeks, but that is not frequent enough to reduce established populations. Baiting points should be checked and refreshed daily, until the population is brought under control. Traps are a useful method of assessing rodent numbers.

One of our monitored farms was catching 100 mice a day in traps at the start of the pest control programme, but numbers eventually went down to fewer than three a day after bait was used regularly and it is possible to totally eliminate rodents by effective baiting.

Clean up feed spillages and broken eggs and repair any machinery that is adding to the problem. Incinerate spoiled feed or remove to a landfill site, because it will be available to rodents, even if it is swept into a deep pit. Clear any surrounding undergrowth that is providing cover for mice and rats.

Rodent bait types

It is best to consult a specialist before selecting bait, although most products are based on anticoagulants. Palatability is the main issue, but bait additives that successfully attract rodents on one unit are not always as effective on the next, so it is worth trying a variety of different formulations, including cut grains, seeds, wax blocks and pasta based sachets.


Insect pests

Flies and beetles can transmit Salmonella, so they should be strictly controlled. Scientists have also confirmed that the disease can be carried by red mites in a laboratory situation, although there is no proof that it can be passed on in the same way in the field. But mite infestation can weaken the bird, making it more susceptible to infection.

What should I do if my flock tests positive?

The key is to identify contaminated houses by effective monitoring and take special care to avoid disease transfer, especially via rodents moving into adjacent housing after depopulation.


Dry washing will not work in contaminated housing. But wet washing can make the problem worse if it is not done correctly, as Salmonella can thrive on any damp waste left behind. The acidification of water before bird removal will help to reduce contamination before cleaning begins.


Consider employing a specialist contractor for disinfection. Some professionals use a 10% formaldehyde solution, applied with a power washer. Although it can be expensive, it is usually more successful than other methods and can lead to better bird performance afterwards.


The normal period allowed for cleaning between batches is not generally sufficient to eradicate a serious Salmonella problem, so it is best if birds are removed from the unit at least a week earlier than usual.

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