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Salmonella sampling regime

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

 
Mark Williams
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To whom do the rules apply?

The rules apply to pullet rearers and all laying flocks producing eggs that are graded under the Egg Marketing Regulations.

How is the term ‘flock’ defined?

A flock is a group of birds sharing the same airspace, so each shed must be tested separately. For free-range flocks in small mobile buildings, birds sharing the same range are classified as one flock.

What does sampling involve?

Pullet rearers

Rearing flocks are subject to the mandatory testing of chick box liners and dead-on-arrival chicks (DOA). On delivery, 10 box liners should be retained by the producer and sent off in a sealed bag to a DEFRA-approved laboratory along with any DOA chicks. At 14 weeks, or two weeks before the birds are moved to layer accommodation, flocks have to be sampled again using 2 pairs of boot swabs if floor reared or pooled faeces if cage reared.

Layer flocks

After moving to layer accommodation, all layer flocks require testing every 15 weeks, starting at 22-26 weeks of age. There is also be a supervised, official sampling of one flock a year on each holding handling more than 1000 birds a year, which will include additional boot swabs or a dust sample.

Sampling options

There are two main sampling options for birds in lay. Boot swabs are used for birds on litter/slats and faecal samples for birds housed in cages. If an operator sample tests positive for S Enteritidis or S Typhimurium a repeat sample is normally taken. If positive, producers can choose to have samples of the caeca and oviducts of 300 birds or 4000 eggs (pools of 40 eggs) tested.

How can producers avoid a false positive result?

The risk of getting a false positive result has been over-exaggerated within the industry. But it is possible for contamination to occur through Salmonella carried in dust from feed brought into housing or lack of care with taking boot swabs when there are other species such as pigs or cattle on the farm.

Bulk feed bins can sometimes carry Salmonella. If dust originating from feed piped into the housing is sampled, it can result in what has been termed a false positive, because this dust doesn’t necessarily cause infection in the birds.

It pays to make sure the person taking the sample observes good hygiene measures, to avoid the possibility of contamination from one house to another, or from other animals the sampler has been in contact with.

Samplers should use sterile gloves and containers and observe good biosecurity between units. Live vaccines can also cause problems if samplers have previously been handling vaccination products. There is also a risk when sampling recently vaccinated flocks.

Laboratory techniques will identify the differences between live vaccine strains and field strains, but the results may take some time to confirm. In the meantime, the producer is subject to a lot of worry.

Wild birds can carry types of S Typhimurium that do not normally end up contaminating eggs. But even if scientists believe that wild birds have caused the infection, the regulations still apply.

Boot swabs

The cheapest option is to buy disposable "mob" caps, used by the food industry. They should be moistened with clean tap water before sampling and go over the top of boots and plastic boot covers. Two separate pairs of boot swab samples per flock taken from the whole length and breath of the house, including littered and slatted areas, are required to meet the rules. Care should be taken to avoid the risk of the sample being affected by foot dip and other disinfectants by putting on plastic over boots after entering the poultry house.

Faecal sampling

For layers in cages, faecal samples should be collected from the ends of all available manure belts across the house. Belts should be run before or during sampling to accumulate faeces on the scrapers at the end. If there are no belt scrapers, material from the belts should be swept up with a sterile gauze swab or gloved hand as it passes over the end of the belt. Samples are then mixed together to form two separate 150g composite faecal samples from an initial collection of 2-3kg of material.

The caged-pullet faecal test requires 60 x 1g samples collected from across the cage house in a similar way.

Annual official test

Once a year, samples need to be taken in the presence of a designated official.

This sample has to be taken from one flock on each holding of more than 1000 birds a year. For a producer with 10 flocks just one flock will be sampled.

Additional faeces or boot swab or dust samples as well as faeces need to be taken. The official sample will replace one of the regular operator samples. Dust sampling can be a highly sensitive indicator of whether Salmonella is present, as excreted Salmonella that is no longer detectable anywhere else in the birds’ environment can survive in dust.

How much will the sampling cost?

The processing charge should be about £100 a flock cycle, excluding the official sample testing.

What will happen if a flock tests positive?

Since 1 January 2009, a flock that tests positive for either of the two target Salmonella strains has been blighted for life after confirmatory tests. It is likely that positive pullets will have to be destroyed. Eggs will require heat treatment and, therefore, cannot be sold on the retail market.

Eggs from an infected flock achieve very little realisable value. For flocks in the last weeks of lay, returns may be enough to cover feed costs. However, the financial effect is much more serious for producers with pullets or layers at earlier stages of their cycle.

It is difficult to find a processor prepared to take eggs from a flock under suspicion, placed under restrictions until testing is finalised. In most cases there is no alternative but to cull the flock and start again, but insurance cover is available for this and culling the flock gives the best chance of avoiding persistence of infection on the site.

How do producers get back into the main market after a positive result?

After culling, producers are strongly advised to make every effort to eradicate any trace of Salmonella in their buildings and any farm pests before restocking. Enhanced vaccination programmes should also be discussed with the veterinary advisor for the site.

Want to know more?

salmon-testing1

For deep-pit systems, representative samples of manure should be taken from each row in the pit…

salmon-testing2

…while in litter systems, samples should be taken from 60 different locations in the house.

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For boot swabs, the cheapest option is to buy disposable mob caps.

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Samplers should use sterile gloves and containers.

salmon-testing5

The area under under the ramps is a good place to sample, but all official salmonella sampling is carried out within houses.

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Dust samples are required as part of the annual official test.

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