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Going with the flow: How to maximize the effectiveness of spray vaccination

6 September 2021, at 9:47am

Attention to detail is vital when it comes to ensuring that spray vaccinations against respiratory diseases such as infectious bronchitis are as effective as they can possibly be, according to a poultry health expert.

Brian Jordan, associate professor at the University of Georgia, said how the vaccine is mixed, the syringes and nozzles used, and the flow rate coming through the nozzles are all critical elements to vaccine-application efficacy and should not be overlooked.

While US producers typically use 7-mL volumes of vaccine, in recent research, Jordan and his team investigated what larger volumes would do to application success rates.

“We found that if you use a larger volume of diluent when you dilute your vaccine — so you give the same doses, just in a larger liquid volume — you get a better vaccine,” he told Poultry Health Today.

To get that result, though, increased flow rate through the nozzle is required, so there isn’t much added pressure or added shearing force. This means you get bigger droplets of the vaccine reaching the chicks.

There is no optimum pressure, Jordan said, with nozzle choice and volume the deciding factors.

“If you’re using a smaller volume, say 7 mL, with a small nozzle you may use a lower pressure than if you’re doing a larger volume, say 14 mL or 21 mL, in that same nozzle. So, the pressure is that one variable that is the last one to be set,” he explained.

“Once you decide on which volume you want, which nozzles you want to use and how many nozzles…then you adjust your pressure [so the] application meets the speed of your chicks moving through your application system.”

Getting recommendations from spray-cabinet manufacturers following an audit of the hatchery is the best way to ensure the right nozzles, volumes and pressures are used, he added.

Live monitoring keeps track of the details

On the day of vaccination, evaluating a live system in real-time can be difficult, but a piece of plexiglass or thermal imaging camera can help to judge spray evenness and the coverage of chicks going through the system.

Jordan recommended installing the plexiglass inside the basket, but not all the way to the bottom, and doing a test-run to see how well the screen is covered by the spray.

Alternatively, the vaccine’s temperature as compared to chick body temperature means there’s a considerable contrast using thermal imaging, allowing the minor details of spray coverage to be observed.

“Maybe the spray is starting a fraction of a second too late and you’re missing the front of the basket, or maybe your spray is stopping a fraction of a second too early and you’re missing chicks in the back of the basket,” he said.

He also noted that thermal imaging has an additional benefit for monitoring how chicks are stacked in the holding room, following vaccination, through a greater understanding of air flow, warming and cooling, as well as providing a clear view if stacks are too close together, with chicks panting, or fans directly on chicks chilling them and causing them to huddle.

Creating a useful data set

Vaccine surveillance, or vaccine takes, is a useful tool, particularly if you’re considering making a change in vaccine-cabinet manufacturer or vaccine type, Jordan said.

In his work, producers take samples from birds aged 5 to 7 days, which are sent for analysis by real-time polymerase chain reaction (PCR) to determine which birds actually received the vaccine.

Of those that did, the viral load is also measured, allowing the reality of vaccination to be tested against expectations, which may in turn guide improvements in processes.

“The problems could range from anything from vaccine handling errors, mixing errors [and] application errors, to even all the way back to manufacturing issues with the vaccine itself,” Jordan explained.

This is where his team’s analysis can be invaluable, he added, as they can evaluate data and advise on what the issues could be, or whether the results are normal for a particular vaccine.

Taking the long view of vaccination success

The benefits of such diagnostic technology are that it can provide a baseline for a hatchery or farm, which can then be used to assess the impact of any changes on vaccination efficacy further down the line. Sampling the right number of birds in the right places makes all the difference.

“We recommend doing 15 per house and then doing six houses; you can spread those six houses across six different farms if you’d like,” Jordan said.

“This gives us a total of 90 samples, which is basically the capacity that we can run on one standard real-time PCR plate. So, it maximizes efficiency [and] reagents. It’s the way to most effectively use the cost involved when running these assays.”

In addition to doing vaccine-take surveillance, older birds are also sampled to assess vaccine longevity, at what point they clear and to see if any other viruses are coming into the flock. This can sometimes lead to the detection of new variants.

Jordan recommended vaccine-take surveillance be carried out once a quarter, supplemented by challenge-virus surveillance in older birds at roughly the same frequency. When necropsies are being carried out on those at the end of the grow-out period to assess gut health, tracheas can be removed and sent in for analysis.

“You get a sampling of a variety of ages of birds, across farms,” he explained. “A lot of times it may be within a couple of different hatcheries if it’s a big complex, and so you get a lot of data doing that.

“That way you don’t have to go in and unnecessarily euthanize birds that would be in production,” he added.