In association with Poultec Training Ltd
Producers have had to get to grips with the sampling regime required by the salmonella rules. The Veterinary Laboratories' Agency's Rob Davies and British Egg Industry Council's Mark Williams offer some tips.
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 mobile buildings, birds sharing the same range are classified as one flock.
What does sampling involve?
Pullet rearers
Rearing flocks aee 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.
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 a dust sample.
Sampling options
There are two main sampling options for birds in lay. Boot swabs are used for birds on litter and faecal samples for birds housed in cages. But if a sample tests positive for S enteritidis or S typhimurium a repeat sample is 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.
Bulk feed bins can 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 go over the top of boots and plastic boot covers. Two separate pairs of boot swab samples per flock 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 on litter, faecal samples should be collected from 60 different locations in the housing and then mixed together to form two separate 150g composite faecal samples from an initial collection of 2-3kg of material. Where the producer uses A-frame step-cage houses, representative samples should be collected from the ends and middle sections of each row of manure in the deep pit.
The pullet faecal test requires 60 x 1g samples.
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.
Dust samples as well as faeces need to be submitteds. 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.
The BEIC is negotiating with DEFRA over the fine detail of the annual visit. We feel that the producer should be able to determine which flock is sampled.
We have also said that as the producer will be paying for the cost of the official sample, as well as for the 15-week samples, there is no reason why DEFRA Animal Health Agency staff alone should be employed. An independent control body could provide the necessary degree of competition.
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 testeds positive for either of the two target salmonella strains has been blighted for life after confirmatory tests. It is likely that 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 could 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 will be much more serious for producers with pullets or layers at earlier stages of their cycle.
It may be difficult to find a processor prepared to take eggs from a flock under suspicion, placed under restrictions until testing is finalised. He advises that in some cases there may be no alternative but to cull the flock and start again.
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 before restocking.
Want to know more?
For deep-pit systems, representative samples of manure should be taken from each row in the pit...
...while in litter systems, samples should be taken from 60 different locations in the house.
For boot swabs, the cheapest option is to buy disposable mob caps.
Samplers should use sterile gloves and containers.
The area under under the ramps is a good place to sample, but all official salmonella sampling is carried out within houses.
Dust samples are required as part of the annual official test.