Looking at broilers with Salmonella typhimurium or Salmonella enteritidis, a producer or even a vet for that matter, would not necessarily know they had it, writes Marianne Curtis.

Poultry Health Services vet Elliott Boyd says that sometimes they show lethargy or poor growth but can also show these when suffering from other diseases. 

See also: Three ways to reduce salmonella risk on poultry farms in summer

“The only way to find out is by testing, which happens under the umbrella of Defra’s National Control Programme (NCP) for Salmonella in broilers and was introduced in 2009. 

“It has a target of 1% or less positive flocks out of the total number of flocks tested per year for the two regulated strains – Salmonella typhimurium and Salmonella enteritidis [which have the potential to cause illness in humans]. 

“It is under 1%, so it must be doing its job.”

Under the NCP, broilers must have a negative test within three weeks of slaughter. 

Testing methods

There are three testing options – dust, faecal and boot. Most producers opt for boot testing, says Elliott. 

Farmers pay for the equipment for testing and the lab fees. Samples must go to a UKAS-accredited laboratory for testing and must arrive at the lab within four days of sampling to be compliant.

Where Salmonella is presumed but the type isn’t known, serogrouping into one of the larger groups – A to G is carried out, which takes around four days from receipt of samples, explains Elliott. 

“The serogroups containing Salmonella strains of potential concern for human health are B and D. All samples positive for Salmonella are sent to the Animal and Plant Health Agency (APHA) for further testing. 

“Here they are cultured and subsequently undergo PCR testing (five days) for confirmation of strain as well as serotype.

“Include weekends, and the flock can be positive for quite a long time. If it doesn’t test positive for serotypes B or D, it can go for slaughter as normal but is usually slaughtered at the end of the day. 

Processors won’t take birds from serogroups B or D until APHA confirms the strain is not a regulated one. Birds found to be positive for the regulated strains, i.e. Salmonella typhimurium and Salmonella enteritidis, are culled on farm.”

Next crop

If a farm tested positive for a regulated strain in the last crop, APHA will go to the farm early in the next crop to conduct tests to ensure the site doesn’t continue to test positive. 

Until recently, APHA would also conduct advisory visits to farms which had recently been infected with regulated Salmonella strains, however, Avian Influenza has put pressure on this service, and these tend to be fewer, says Elliott.

“I am constantly speaking to farmers about biosecurity. Recently, we have found Salmonella typhimurium in broiler units a few hundred metres from infected pig units. 

In the summer these units attract many flies which could carry and spread it. Rodent control is also very important to prevent spread.”

After one positive test for a regulated Salmonella strain, there is no official length of time before producers can restock. 

Sampling

However, if the farm has a second positive test, which can occur, this means applying to APHA for a licence to move any birds or equipment off farm.  

The agency must also supervise washing and disinfection as well as carrying out official sampling on the empty sheds post cleaning – a negative test is needed before APHA will allow the farm to be restocked.

The financial consequences of being positive for Salmonella typhimurium or Salmonella enteriditis are large, says Elliott. 

“Any days when there are no birds in the sheds, producers are losing money. Not being able to do the normal crop turnaround is a cost. Last year it cost one of our clients £250,000 for two sheds.

“The cost depends on how many birds you have, how old they are – the older they are, the more food they will have eaten before culling. 

Also, the energy cost of getting them to a particular point. There are also cleaning costs, particularly if you have to do a second cleaning because site samples come back positive. And food can go mouldy when there are no broilers in a shed to eat it.”

Government guidance – boot testing

Take two pairs of boot swabs from each house on site. Moisten the boot swabs with water before you take samples. Avoid disinfectants and hand sanitisers with your boot swabs.

Divide the house into two equal parts for sampling and use one pair of boot swabs in each part. 

Take at least 100 steps with each pair of boot swabs, walking around 50% of each part. Drag your feet on the floor to pick up as much material as possible. If the house is divided into several pens, spend more time in the larger pens and less in the smaller pens.

When you’ve finished sampling, take the boot swabs off and turn them inside out carefully so that the material you’ve collected stays on them. Put the boot swabs together in a sealable bag to send to the laboratory.