How does site of injection affect the immunology of a bird when vaccinated in ovo? This question was addressed at the 2009 Poultry Science Association Meeting where Brett Hopkins, MS, DVM, PhD, DACPV, associate director for outcomes research with Pfizer Animal Health, presented data from a large scale commercial hatchery trial comparing the only two commercially available egg injection systems in the United States.

When comparing the accuracy of delivery to the correct site of injection, Dr Hopkins found that Pfizer's Embrex® Inovoject® System exhibited significantly greater correct in ovo site of vaccine delivery (95.3 per cent) as compared with in ovo delivery using Avitech's ManualJect^TM System (52.3 per cent).

In conjunction with Chris Williams, MS, PhD, director of poultry technical services Pfizer Poultry Health, Dr Hopkins designed the trial to evaluate the quality of vaccine delivery as measured by site of injection in ovo, noting that the ability to provide protection against disease after hatch begins with the vaccine being delivered to the correct site of injection in the egg.

"Proper vaccination should be the primary criterion used to evaluate an in ovo injection system because uniform vaccine delivery may provide earlier immunity to diseases when performed correctly," stated Dr Hopkins.

Proper sites of injection were defined as the amnionic sac, subcutaneous injection to the breast, intramuscular injection into the breast or any combination of the previous. Injection and vaccination of the air cell, allantois, yolk sac, a combination of these sites, or no vaccine deposited at all, were classified as improper and therefore provide questionable disease protection.

A 2000 study demonstrates that the efficacy of vaccines delivered in ovo into the amnion or embryo is greater than 90 per cent, regardless of day of injection and breeder flock type, while vaccines delivered in ovo via the allantois or air cell are less than 50 per cent effective in providing disease protection ¹.

"Application of the vaccine in other areas of the egg has also been shown to greatly reduce the protective index against disease challenges," said Dr Hopkins.

Comparison of In Ovo Vaccine Delivery

Overall, the Inovoject System performed 871 total injections to eggs with viable embryos while the ManualJect System injected 930 eggs with viable embryos. Of those 871 viable eggs injected by the Inovoject System, 830 or 95.3 per cent were performed at the proper site of injection. The ManualJect System delivered only 486 or only 52.3 per cent at the proper site of injection.

Comparison of In Ovo Vaccine Delivery Systems By Injection Site

Comparing the different injection sites occurring in good eggs, the Inovoject System injected 730 eggs in the amnion and 95 in the embryo, classifying them as proper injections. In comparison, the ManualJect System had only 336 amniotic injections and 135 embryonic injections, followed by 185 combination injections occurring in the allantois and amnion, which is considered an improper injection.

This study uncovers a primary question of concern when injecting in ovo: Why should producers be concerned about where a vaccine is delivered? Vaccine delivery is critical to an embryo's integrity and survival and its proper immunization for protection against disease challenges.

"Conducting large-scale evaluations in a commercial setting such as this, establishes relative value and importance of proper in ovo injection for our customers," stated Dr Hopkins. "The objective of this trial was to reassert the importance of site of injection in ovo and its vital role in providing early, effective and uniform protection against disease."

Reference

¹ Wakenell, P. et al. 2000. Effect of in ovo vaccine delivery route on herpesvirus of turkeys/SB-1 efficacy and viremia. School of Veterinary Medicine, University of California Davis. 2000; 274-280.

July 2009