Salmonella Control in Backyard Poultry

Why are you keeping chickens?

This is the first and most important question. The answer will affect how much effort and money you are prepared to invest in a) controlling the likelihood of your chickens becoming infected and b) the true cost of minimising the risk of salmonella being associated with the egg that is consumed.

Current best practice is aimed at the commercial poultry industry where one flock will consist of thousands of hybrid laying hens. Vaccines, Competitive Exclusion Products, hygiene products, housing and monitoring have been developed for large flocks.

You have chosen, perhaps unwittingly, to keep chickens in the most challenging of husbandry environments. The following notes are intended to provide information on the possibilities available to you so that you continue to derive pleasure and enjoyment from keeping poultry. More detail can be found in my PHC Library.

Background to Salmonella infections

Salmonella infections are caused by the salmonella bacteria of which there are over 2,500 different strains. They can be divided into those that are host adapted of which there are only a few. For example, Salmonella Pullorum (Sp) and Salmonella Gallinarum (Sg)infect birds but not usually mammals whereas the majority are not host adapted infecting birds, mammals, reptiles and fish. These are known as the paratyphoid salmonella. Salmonella have also been found in insects.

Salmonella Enteritidis (Se) and Salmonella Typhimurium (St) are the two commonest causes of salmonella food poisoning in humans.

Remember, should your chickens become infected with any salmonella but especially Se or St and subsequently an outbreak of food poisoning is associated with eggs from your flock. Then the flock may have to be slaughtered.

How many chickens do you have laying eggs for human consumption?

Current legislation distinguishes between flocks of less than 50 chickens, flocks between 50 and 350 chickens and flocks with more than 350 chickens

  • If you have more than 50 chickens you will need to register with the Great Britain Poultry Register.
  • If you have more than 350 chickens you will need to be registered with DEFRA’s Egg Marketing Inspectorate under The Registration of Establishments (Laying Hens) Regulations 2003
  • You will also be working to the Eggs and Chicks (England) Regulations 2009.

Even if you have less than 50 chickens laying some of this legislation may apply depending on how and where you sell your eggs.

How may your chickens become infected with Salmonellae?

There are two routes:-

  1. Vertical transmission. A few strains of salmonella are capable of being passed in the egg. These include Sp, Sg (the two avian salmonella), and Se.
  2. The majority of salmonella, including those above, are mainly excreted with the faeces.

Remember chickens will peck at anything including faeces.

What measures can be taken to reduce the risk of salmonella in or on the eggs you eat or sell?

The use of vaccines, competitive exclusion products, biosecurity and monitoring will help reduce the risk of salmonella infections.


  • There are live and dead vaccines available which should be administered according to the manufacturer’s instructions during rear and before point of lay.
  • The vaccines are not designed for use in hens that are laying eggs. Live vaccines should never be given to hens that are laying eggs
  • These vaccines may provide protection against either Se or St or both.
  • They will not provide complete protection against infection from all strains of salmonella.
  • They will protect the chicken from clinical signs of disease if they are likely to be infected in the first four weeks of life.
  • They will minimise the likelihood of spread of Se from the gut to the ovary.
  • They will reduce the number of Se and St bacteria excreted in the faeces.
  • They offer greatest protection against Se and St as appropriate for the vaccine.
  • They will not provide complete protection from gut infections in the event of excessive challenges.
  • They are designed to provide immunity for one laying cycle of about 52 weeks.

With minimum pack sizes of 1,000 doses you may be best advised to buy vaccinated POL pullets and then use a Competitive Exclusion Product.

Competitive Exclusion Products

These products contain the normal bacteria, hundreds of different species that are found in the caecum or blind gut of the chicken. These bacteria attach to and line the gut. Effectively, these “good” bacteria block the attachment sites for salmonella and also produce products that inhibit salmonella growth.

The advantage of these types of products is that they are effective against all salmonella.

Competitive exclusion products are not the same as probiotics. The latter contain one or a few species of bacteria. In tests, they have been shown to be much less effective in preventing salmonella colonisation of the gut.

I would recommend using Aviguard. This is available from Microbial Developments Ltd (MDL). It comes in various pack sizes to suit the smallest and largest of flocks:

· Beryl’s Friendly Bacteria (6 – 12 hens) –· Flightpath (50 + hens) –· Aviguard (2000 + hens) – through your vet, animal health distributor or failing that contact MDL through their website.


This is a huge subject and an extremely important aspect of salmonella control. It brings together all aspects of disease control. This includes an appreciation of the sources of infection, how infection can spread, how infection can be recognised and what can be done to prevent or limit the risk of infection.

  • Obtain replacement day olds or pullets from salmonella free flocks.
  • Ensure feed and water cannot be contaminated with faeces.
  • Use water sanitisers e.g. AviForte –
  • Minimise contact with wild birds, rodents, pets, farm animals, people.
  • Minimise the risk of walking infection from one flock to another with the use of foot dips and hand sanitisers.
  • Always have clean hand washing and toilet facilities. Ideally, have a changing area where you can take off overalls and footwear before going into your home.
  • Keep your Veterinary Health Plan up to date.

Monitoring for Salmonella

Most salmonella infections do not show any clinical signs in chickens. As a minimum you should comply with the National Control Programme for Salmonella in Laying Hens.

How often and what type of sample?

AgeSample as per the National Control Programme
Chick1 chick box liner per 500 chicks up to 10 chick box liners.

Dead on arrival chicks

Rearing Pullet2 pairs of boot swabs or one large faeces sample 2 weeks before being moved to the laying houses.
Laying Hen2 pairs of boot swabs or 2 x 150g faeces samples taken between 22 to 26 weeks of age. These should be repeated every 15 weeks thereafter. If you start at 22 weeks then the next 3 sets of samples will be at 37, 52 and 67 weeks of age or if you start at 26 weeks then it will be 41, 56 and 71 weeks of age.

There is no reason that you should not sample more frequently, if you wish.

Where to get the testing done?

Only use DEFRA accredited laboratories for your testing. The laboratory can supply all the testing kit and instructions for use.

  • Poultry Health Services Ltd. Tel. 01480 462816
  • Sci-Tech Laboratory Ltd. Tel. 01588 672600
  • Wincanton Laboratory Ltd. Tel. 01963 435605

Further Reading

Please note that these guides and recommendations may change. In case of doubt please refer to the original source – DEFRA or Business Link

Summary Plan


Pre- HousingDisinfectionThorough cleaning of housing and equipment prior to arrival.
Pre- PurchaseCertification of Freedom from SalmonellaCould be part of a flock passport.
Day OldLive Salmonella vaccines



At times of high risk and large flock size


Low risk and small to large flocks

Day OldSalmonella samplingChick Box liners and Dead on Arrival
Alternate weeksAviForte in the drinking water – 0.325ml /litreDo not mix with live vaccines or any other treatments.
3 weeks plusLive or dead salmonella vaccines used according to manufacturers instructionTo be given to birds in rear. This may be part of a planned programme which will include protection against other infections e.g. Infectious Bronchitis, Newcastle disease, Coccidosis, Infectious Laryngotracheitis, Mycoplasma gallisepticum
2 weeks before move to laying quartersSalmonella sampling2 pairs boot swabs. These are swabs placed on your boots. You then walk around the housing and any salmonella present in the littered on slatted areas will be collected.
MonthlyAviguard in the drinking water or on foodParticularly in laying flocks where the smaller numbers mean that vaccination is uneconomic.
MonthlyClean and disinfect Feeders and drinkersMore often if necessary
From 22 weeks – every 15 weeksSalmonella sampling2 pairs boot swabs.
About David Parsons 19 Articles
David Parsons began his veterinary career in mixed practice which triggered his 39-year passion for poultry. Following positions as a veterinary research officer in the Poultry Department at the government’s Central Veterinary Laboratory and then as a poultry company veterinarian, he set up his own poultry veterinary practice in the southwest of England in 1985. He obtained his MSc in Applied Immunology in 1981, Certificate in Poultry Medicine and Production in 1989 and a Nuffield Farming Scholarship Trust to study the“Status of diseases specific to poultry and their control in Europe” in 1991.

He has been an Honorary External Lecturer at the University of Bristol Veterinary School on poultry medicine and production since 1999,a lecturer on the Institute of Animal Health’s poultry disease course since 2000 and is a regular monthly contributor of veterinary articles for backyard poultry keepers in the Practical Poultry magazine.