With more than 25 billion broiler chicks receiving sub-cutaneous (SQ) vaccination in the hatchery last year, the method accounted for 70 percent of all hatchery vaccinations given. SQ vaccination is simple and economical, however, there are various factors that can dramatically affect vaccination performance and so merit extra consideration.

Good SQ vaccination coverage is generally seen as being in excess of 98 percent. This means that at least 98 percent of the day-old chicks receive the correct volume of vaccine, at the correct location on the neck, and without suffering significant injuries or too much stress.

It is also important to remember that vaccination must occur without contaminating the chicks, which can be a weak point with SQ vaccination.

An operator-based process

On average, one SQ operator can vaccinate 2,500-3,000 day-old chicks per hour. In most cases, however, this volume can only be maintained for a maximum of six hours.

Larger vaccination rounds, or higher speeds, can result in lower vaccination quality due to tiredness and a lack of accuracy. The average operator can vaccinate a maximum of 18,000 day-old chicks per day, evidence suggests that larger outputs tend to result in an increase in the incidence of culled chicks, injured chicks and wet fluff chicks.

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It should come as no surprise that the quality of each operator’s skills can dramatically affect the hatchery’s overall vaccination efficacy.

For example, the way that chicks are handled and positioned over the injection plate is crucial and must be performed correctly for optimal results.

For a 150,000-day-old-chicks-per-day hatchery, one operator represents roughly 12 percent of production – a high percentage. Because of this, continuous training of the vaccination staff, continuous monitoring of activities, and continuous evaluation of the vaccination performance of each individual is needed.

Only by developing a refined vaccination technique can operators achieve a consistent vaccination quality over time, day after day. 

SQ equipment: A limiting factor

Even the most skilled vaccination operator, however, cannot achieve target vaccination levels if the equipment is not good enough.

The condition and quality of equipment, together with operator skills, are the main factors that need to be optimized. Equipment must be perfectly clean, well maintained, and perfectly adjusted day after day.

Simple and small mistakes in needle and equipment adjustment - needle length, air pressure supply, sensor location, and so on – can all lead to significant problems, and will have a direct impact on vaccine location, dosage and the rate of injury.

It is almost impossible to reach constant and high vaccination quality ratios if the equipment in use is not high quality.

Benefits of investment

Modern devices include the latest technology and materials to be more accurate, and their performance is higher than older models. However, it is not uncommon to see SQ machines that have been in operation for 5-10 years.

Additionally, the composition of vaccines themselves has changed. Newer vaccines can be more fragile, and sometimes require the use of patented and/or specially designed syringes or applicators, such as double injectors or special vectorised HVT cell-care syringes. Investing in the latest and highest-quality equipment should always be considered, and the return on investment can be quite fast.

And it is also important to remember where equipment is concerned that it must perform consistently and homogeneously. Variation of +/- 3 percent in dosage are unacceptable and need to be corrected immediately. As a rule of thumb, dose homogeneity is a good indicator of the SQ equipment: The more accurate and constant the dose, the better the quality and reliability of the equipment.

Monitoring: the way to succeed

How can results be improved if you do not know where improvements need to be made?

The obvious consequences of poor SQ vaccination location in comparison with accurate application can be seen in Image 3. Using a blue dye with the vaccine is best way to monitor vaccine application performance. Despite the obvious damage harm done to day-old chicks and vaccine waste that results from errors of this type, there is a bigger underlying consequence: lack of field protection against viruses.

This is simply one example of the types of issues related to incorrect SQ application. However, there are several other issues that could arise as a result of incorrect vaccination (see Table 2). Each of these vaccination failures results in a specific post-vaccination issue, and it is the role of the hatchery vaccination manager to monitor each of these potential errors on a regular basis, operator by operator. Should any of these specific failures be detected immediate corrective action should be taken.

SQ vaccination is a highly popular and convenient method of vaccination. It can achieve high levels efficacy and coverage, but is highly dependent on two factors – operators and equipment. Only trained and skilled operators, together with good quality modern equipment can guarantee a constant and homogeneous vaccination efficacy ratio, and constant monitoring and preventative maintenance of equipment are essential to ensure that vaccination crews meet their targets.