Even millimeter-level misplacements of in ovo vaccines can dramatically reduce immune response in the chick, leaving poultry flocks vulnerable to disease outbreaks despite vaccination efforts.
“Vaccination accuracy is one of the biggest determining factors of whether a vaccine is going to stimulate an immune response and therefore provide protection to that bird for the targeted diseases,” explained Dr. Josh Deines, technical service device lead at Zoetis. “When it comes to in ovo vaccination, where the vaccine is delivered within the egg significantly impacts its effectiveness.”
For example, when vaccines are accurately delivered to the embryo body or amniotic fluid, they can provide more than 93% protection against disease. However, misplaced injections into locations like the allantois reduce protection to 28% or less, while air cell injections provide virtually no protection at all.
How poultry vaccination can go wrong
The process of in ovo vaccination creates multiple potential failure points that can go unnoticed. Bent needles, one of the most common issues, can redirect vaccine placement away from target locations. Gaps in day-to-day equipment maintenance can contribute to equipment problems. For example, slipping tooling — often caused by water or sanitizer leakage onto injection heads — prevents stable positioning during the injection cycle.
Embryo development timing also plays a critical role. The acceptable transfer window ranges from 17 days, 12 hours to 19 days, 4 hours of incubation. Transferring too late reduces accuracy as embryos fill the shell and begin to hatch, increasing the risk of eye or other undesirable vaccination locations. Conversely, transferring too early or with poor incubation conditions can result in abnormally developed or mispositioned embryos.
In addition, “if there’s abnormally developed embryos mispositioned due to extreme overheating or under heating during incubation, then they may also have the vaccine delivered to the wrong location,” Deines noted.
Follow a QC checklist
Implementing a comprehensive quality control (QC) checklist can significantly improve consistency of vaccination accuracy. Key inspection points include running QC plates at the frequency recommended by the technology manufacturer to ensure every needle deposits vaccine properly, visually checking for bent needles by examining injection tooling from a 45⁰ angle and monitoring for slipping tooling throughout the injection process.
Environmental controls are equally important. Hatchery managers should avoid transferring embryos into dirty, wet or cold hatch baskets, and protect injection equipment from water leaks and excessive humidity that can compromise tooling stability.
“There’s no reason not to do it,” Deines emphasized regarding the QC checklist. “It’s such an easy task requiring little time and it can significantly impact results.”
For hatcheries processing millions of chicks monthly, even small improvements in vaccination accuracy can translate to substantial economic benefits.