The importance of understanding how to achieve the highest efficacy possible when using spray vaccination should not be underestimated, especially given that more than 95 percent of the world's broilers and 100 percent of layers and breeders are now spray vaccinated in the hatchery.

There are five points that need particular consideration along the process.

1. Coverage: 80 is not 100

Ensure your equipment has the right capacity and is properly adjusted. Coverage must be as close as possible to 100 percent.

While obvious from a mathematical point of view, when applied to spray vaccination, the consequences of vaccinating only 80 percent of chicks in the crate, rather than 100 percent, can be dramatic. Spray vaccination equipment must be able to cover all of the crated chicks.

Often, spray units are not properly adjusted or of sufficient capacity; the spray nozzle positioning must be even with regard to the crate design and dimensions. In other words, spray systems must be able to adapt to the design of each crate to guarantee 100% coverage.

However, too frequently, an uneven spray distribution is achieved. Twenty percent less vaccination efficacy means that, for a normal 50 million-eggs-per-year hatchery (considering an average 80 percent hatchability), around 8 million birds per year may not be protected in the field.

2. Droplet size and homogeneity: A good average is not enough

If spray equipment cannot deliver a homogeneous and constant droplet size (at least 95 percent accuracy) it should be replaced.

A constant spray droplet size is essential for good spray vaccination.

Depending on droplet size, the vaccine will target different areas and tissues. The finer the droplet, the deeper it will penetrate, targeting the deep pulmonary tissues. A larger droplet will only reach the more exposed mucosa, such as the eyes and nostrils.

Depending on the type of vaccine (mild, intermediate, hot, etc.), and the targeted tissue, a corresponding droplet size must be defined. 

Normally, most hatchery spray vaccination is performed with 150 micron droplets. But this value is not constant, it is simply an average of the total droplet sizes applied.

Why is this so important? 

In picture 2, we can see different distribution curves with the same average (let´s consider 150 microns), but with different homogeneity. The lower the distribution homogeneity in the curve, the more variability in droplet size will be obtained from the nozzle. Keep in mind that, conceptually, if 20 percent of the droplets are, for example, 100 microns instead 150, and 20 percent are 200 microns, it does not mean that 60 percent of the chicks will receive an adequate droplet size of 150 microns. In fact, all the chicks will receive 20 percent of the dose with 100 microns droplets, which is too fine and can lead to post-vaccination reaction and economic losses, and 20 percent of the dose in very coarse spray, ineffective vaccination, poor protection, and economic loss. 

3. Dose accuracy

Only use spray units with top-quality dosing units. Do not use disposable-plastic units. Develop specific monitoring and maintenance activities to audit the vaccination process, minimizing losses. 

If we use the same example of a 50 million-eggs-per-year hatchery, overdosing by 15 percent would waste thousands of Euros, depending on vaccine price, by year-end. In this example, losses would reach Euro36,000 (US$49,500) per year on a vaccine cost ratio of Euro6 ($8.25) per 1,000 doses. 


However, 15 percent overdosing considering 10 ml volume per 100 DOCS, only means 11.5 ml, and losing 1.5 ml per cycle is not that difficult. Normally, what happens is that for a 150,000 DOCs-per-day hatchery, the operator has to prepare approximately 170,000 vaccine doses as the average dosing equipment could have, even in a best case scenario, a 5 percent scaling error. This may be due to poor pneumatic and vaccine line maintenance, leakage, vaccine waste due to priming, end-of-day waste, evaporation and air drift, and operator error. 

Conversely, under-dosing by 15 percent can easily occur due to crate misalignment, uneven chick distribution, etc., and the economic consequences in the field can be quite significant. 

The more precise the equipment and the processes, the smaller the impact on the bottom line. 

4. Operational efficiency in the real world

Optimizing process performance and eliminating operator impact is economically beneficial. Invest in semi-automatic or automatic equipment not based on the push-and-pull approach. 

Any technical input or considerations for spray application must be integrated into a device that is suited to the modern hatchery. 

In the daily running of a 50 million-eggs-per-year hatchery, speed is as important as vaccination efficacy; operational costs are as important as droplet size. 

Additionally, the impact of the operator on the process can be huge. For example, it is widely known that the push-and-pull effect on manual standard spray cabinets can reduce efficacy to 30 percent, meaning that only one-third of the chicks are correctly dosed. 

Modern hatchery vaccination demands automatic or semi-automatic equipment with high outputs, high efficacy and minimum operator impact. 

Operating a standard cabinet manually for more than six hours is tiring and operator performance declines, as does vaccination efficacy, after four hours of work. The return on investment when acquiring an automatic or semi-automatic unit is guaranteed within a few months.   

5. Biosecurity: Getting more and more important

Bacterial contamination is likely to occur within spray equipment and vaccine preparation tools. Develop specific cleaning and disinfection protocols, as 100 percent of production will be exposed.

Traditionally, too little attention is paid to the cleaning and disinfection, with equipment simply used and stored day after day. The situation is worse when considering vaccine preparation (containers, shakers, jars, etc.). 

Given that, most of the time, 100 percent of the DOCs are processed through spray units, the risk of cross-contamination and bacteria growth on the spray equipment is quite high. Our research shows that more than 25 percent of the spray cabinets and in-line units monitored in 2012 showed E. coli prevalence and Pseudomonas sp. presence. 

How should this issue be addressed? 

Cleaning and disinfection protocols must be applied. However, modern spray equipment  should offer automatic cleaning functions, so strengthening sanitation and biosecurity. 

Spray vaccination in the hatchery is an excellent tool to protect birds. However, if not performed properly, it can be a source of direct and indirect losses. From the biosecurity point of view, cross-contamination risk is always present. Investing in the best vaccination equipment and implementing strict monitoring routines are key for success.