Layering IBD vaccines helps bridge immunity gaps in broiler production
Layering vaccines against Infectious Bursal Disease (IBD) can offer broiler flocks added protection to help combat the challenges posed by the costly disease.
While recombinant vaccines provide a strong foundation for IBD control, there is a delay from the time of vaccination to development of full immunity, which can leave birds vulnerable to secondary infections – particularly during the critical early weeks of a broiler’s life.
To close the window of risk, a layered IBD vaccine strategy that combines recombinant vaccines with targeted live vaccines can build a more robust and adaptable line of defense, says Alexandra Mendoza-Reilley, DVM, technical services poultry veterinarian at Merck Animal Health.
“In an ideal world, the maternal antibodies passed from the breeder hen would protect chickens until the recombinant IBD vaccine offers full protection,” Mendoza-Reilley explains.
“But that’s not always the case. Birds might come from multiple breeder sources, with varying levels of maternal antibodies and be placed into environments with different IBD challenges. This creates a window of susceptibility.”
Adopting a rotational vaccine program using products such as Merck Animal Health’s 89/03 and UNIVAX Plus can help producers match real-world field challenges with smarter, data-backed protection plans, she says.
Why recombinants alone might not be enough
Recombinant IBD vaccines, like Merck Animal Health’s HVT-based vector product, are widely used due to their safety, ease of administration and long duration of immunity. However, their effectiveness depends on optimal hatchery application.
“It’s critical the recombinant vaccine is prepared and administered correctly at the hatchery,” Mendoza-Reilley explains. “The IBD recombinant vaccine needs to be properly suspended in the appropriate diluent, applied, ideally, within an hour of preparation and embryos or chicks must receive a full dose. If this doesn’t happen, immunity can be delayed, and the bird may remain vulnerable for longer.”
Even with ideal hatchery application, recombinant IBD vaccines take time to achieve full immunity, usually reaching their peak around four weeks of age (not a USDA claim for the vaccine), according to research & development data. It is during this period of gradual immune development that live vaccines can play a critical bridging role.
Layering for broader protection
Mendoza-Reilley says producers should consider layering live IBD vaccines like 89/03 and UNIVAX Plus in addition to IBD recombinants in situations where maternal antibody levels vary or disease pressure is high.
“89/03 can be used at the hatchery, either in ovo or subcutaneously at day-of-age, and provides protection against classic and variant strains,” she explains. “It’s especially useful in flocks with non-uniform maternal antibody protection, or in areas where early field challenges are likely.”
By contrast, UNIVAX Plus is typically applied via drinking water at around 2 weeks of age. The vaccine, which contains the ST-12 and 51A/C4 virus strains, provides proven performance against both standard and variant viruses1, she says.
“It’s ideal for situations where producers are seeing late-onset IBD issues, such as poor bursal development or inconsistent bursal sizes.”
The flexibility to layer these live IBD vaccines allows producers to respond effectively to field dynamics, Mendoza-Reilley adds.
“It’s not one-size-fits-all. Rotating IBD vaccines can help producers handle changing disease challenges in the field, while using a dual approach of administering a recombinant IBD vaccine along with a traditional live vaccine can offer better control in high challenge situations.” As always, consult your attending veterinarian to determine the vaccination program that best fits your needs.
Informing strategy through field surveillance
Merck supports its layered IBD vaccine strategy with a robust bursal surveillance program, which includes routinely conducting bursal health surveys to assess tissue integrity and histopathological changes.
“If a customer is seeing uniformity issues, smaller birds or inconsistent bursal development, that’s a red flag,” Mendoza-Reilley says. “We collect bursas, score them and perform virus isolation or sequencing to determine if new variants are emerging.”
These insights help producers fine-tune their IBD vaccine schedules, often identifying the optimal time to introduce live IBD vaccines.
“Sometimes it’s not about changing the IBD vaccine. It’s about timing the use of the live IBD vaccine,” she adds.
While layering vaccines might seem challenging from a management perspective, Mendoza-Reilley says Merck Animal Health works closely with producers to make the process efficient and minimally disruptive.
“We usually align our bursal surveys with customers’ existing bird health checks every 4 to 6 weeks,” she says. “And much of the technical support is covered by Merck Animal Health as part of our customer care model.”
Cost considerations are always present, but Merck Animal Health advocates for a proactive approach. “It’s more cost-effective to prevent performance loss than to fix it after the fact. When you see problems emerging, it makes sense to invest in a layered IBD protection program.”
Long-term disease control
As well as short-term protection, Mendoza-Reilley says layered IBD vaccine strategies can help reduce long-term viral load in poultry houses.
“We know viral shedding occurs in all birds when they’re challenged, whether they’re susceptible or vaccinated, and the level of shedding varies depending on the immunity status of the bird.”
“Live IBD vaccines help reduce virus shedding into the environment, when applied alone or in combination with recombinant IBD vaccines,” she adds. “Over time, flock after flock, the layering strategy can lower the IBD challenge level, allowing for a potential return to a recombinant-only program once the pressure is reduced.”
She added that Merck Animal Health encourages producers to reassess their IBD programs every 6 to 24 months. “IBD is a dynamic challenge situation. The IBD field challenge is constantly changing; if you’re not adjusting, you’re falling behind.”
While single-shot, full-coverage IBD vaccines remain the industry’s goal, Mendoza-Reilley says utilizing a layered IBD approach will be essential for the foreseeable future.
“The reality is, we’re not there yet,” she says. “There are too many variables – different IBD strains, different field pressures, and even human factors impacting hatchery vaccine preparation and application.
“Until we can eliminate all those inconsistencies, recombinant and live vaccines, alone or in combination, remain the most reliable way to close immunity gaps.”
Ultimately, Mendoza-Reilley says taking a collaborative, data-driven approach remains key for managing IBD in broilers.
“We have the tools, but it’s not just about the products – it’s about listening to what’s happening on the farm, observing the birds and adapting our IBD vaccination strategy accordingly.”
1Data on file, Merck Animal Health.
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