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Details matter when it comes to ILT vaccination success

18 May 2021, at 3:14pm

Attention to detail is key to successfully vaccinating broiler flocks against infectious laryngotracheitis (ILT), according to a poultry health expert.

Tim Cummings, DVM, senior technical services veterinarian, Zoetis, said managing ILT outbreaks can be a struggle for some producers.

But with careful administration of vaccines — and paying close attention to flock reactions — it is possible to control outbreaks of the highly contagious virus.

Speaking to Poultry Health Today, Cummings said producers’ primary goal should be to keep ILT off farms through rigorous biosecurity measures, including stringent cleaning procedures and limiting visitors to the farm.

But if they suspect the virus — which is a reportable disease — has made it onto their farm, a positive diagnosis is the crucial first step.

Signs of infection

Classical signs of the disease include blood in the trachea, which causes coughing, gagging and signs of blood on barn walls, while milder forms can cause redness in the trachea and conjunctivitis.

“When you get milder forms, it can be confused with some other respiratory pathogens, such as bronchitis [or] maybe Newcastle disease,” Cummings said. “So, you do need to…take the appropriate samples and get them to a diagnostic lab.”

Once a case is diagnosed, an infected farm should be quarantined, and neighboring farms should be notified due to the virus’ ability to travel on the air between barns.

Producers can attempt to control an outbreak through controlled processing, he said, but if the virus spreads to other farms, vaccination is the next step.

Vaccination options

For broilers, the main vaccination options are vector vaccines, which are administered in ovo and utilize pox or Marek’s disease as the carrier, or live vaccines.

“Primarily, we use CEO (chicken embryo origin)-type LT live vaccines to give broilers in the field,” he said, explaining that they tend to be administered at 12 to 14 days of age, though it is possible to administer them from 10 days. “It’s the best vaccine to induce immunity [and] shut [the virus] down.”

However, regardless of the approach they select, it is critical producers assess their vaccination protocols to give them the best chance of success, he added.

“[The] CEO live vaccine is a harsh vaccine. It will cause reactions, and so we have got to do everything we can to make sure every bird gets a dose…to give us the best chance of reducing the field challenge.”

To achieve this, most producers choose to administer the vaccine through water lines rather than a spray, making it important to check that water lines are properly charged and that birds are appropriately water starved.

Getting timings right

Time of year will impact how long access to water needs to be restricted, and the timing should be carefully managed to prevent birds from rushing the water lines and spilling the vaccine. After administration, the barns should be walked to make sure all the birds access the lines.

“We’ve got a lot of variation in how long it takes for these birds to consume the vaccine,” Cummings added. “Some people go up to 3 or 4 hours. I think we should be shooting for a shorter timeframe, 1 or 2 hours, to consume the vaccine.

“These details make a big difference, because if we’re not doing that, then probably a lot of birds aren’t getting the dose they need…and the birds that aren’t getting vaccinated are the ones that are dying later on.”

Monitor birds

Even following the correct vaccination procedures is likely to result in a low level of increased mortality, Cummings warned, but monitoring the birds closely will help identify where any errors might have occurred during administration.

“The birds will tell you if you didn’t do it right,” he said. “You’ll start having mortality…about 4 to 6 days post-vaccination. You’ll have hotspots or certain houses that will have large jumps in mortality [due to ILT].

“It’s just paying attention to detail and doing it right,” he added. “It means you’ve got to spend time [and] manpower, and it takes effort.”