Newcastle disease rarely makes headlines in the US poultry industry, but that doesn’t mean it has disappeared. The virus remains widespread globally, and U.S. producers continue to rely on vaccination to keep flocks protected and performance on track.
One Newcastle vaccine strain drawing renewed attention is VG/GA. Long valued for being gentle on young chicks, VG/GA works differently from traditional respiratory Newcastle vaccines. Instead of only targeting the airways, it replicates primarily in the gut — a distinction that researchers say may have implications beyond basic disease protection.
According to Chuck Hofacre, DVM, PhD president of the Southern Poultry Research Group and a longtime consultant to the broiler industry, that difference is worth a closer look.
“We’ve always thought about Newcastle vaccination in terms of controlling a respiratory disease,” Hofacre said. “But when you use a respiratory vaccine that replicates in the intestines — especially one like VG/GA that replicates in the gut — you may be doing more for the chick than just giving Newcastle protection.”
Balancing early protection with minimal stress
Advising integrators on vaccine programs requires a balance between building strong immunity and minimizing reactivity, particularly in young chicks. Hofacre said producers are increasingly focused on protecting birds early without compromising performance in the first seven to ten days of life — an interval that often determines overall flock trajectory.
“Early performance is very sensitive,” he explained. “Any vaccine that causes the chick to feel off, not eat as well, or struggle to get started can have consequences later.”
“When a strain replicates in the gut — which is to say, an enterotropic strain — you don’t get the same respiratory reaction you might with something that goes straight to the trachea,” Hofacre said.
How the VG/GA strain became an industry workhorse
VG/GA’s enterotropic nature has helped it become the most commonly used ND vaccine strain globally. Traditional lentogenic strains provided protection but sometimes caused reactivity, especially when used alongside other respiratory vaccinations.
“It was a strain that just didn’t cause nearly the same reaction,” Hofacre said. “It did what we wanted a Newcastle vaccine to do, but without hitting the chick’s respiratory system at a vulnerable time.”
As the industry moved toward more complex respiratory vaccination programs, including combinations with bronchitis or reovirus vaccines, the appeal of a gentler ND option became even more pronounced.
Growing interest in mucosal and systemic immune stimulation
What is changing now is the scientific understanding of how enterotropic vaccines interact with the immune system. Recent research suggests that VG/GA vaccination may stimulate not only local gut immunity but also aspects of systemic defense.
“Any time you stimulate the gut immune system, you’re tapping into a major driver of the bird’s overall immune response,” Hofacre said. “We’re learning that this kind of stimulation may have downstream effects we didn’t fully appreciate before.”
Because VG/GA replicates in the intestine, it engages gut-associated lymphoid tissue (GALT), an extensive immune organ system responsible for detecting pathogens and shaping both mucosal and systemic immunity. Activation at this site may influence the bird’s ability to respond to other antigens encountered early in life.
“That broader immune stimulation is something we’re just starting to understand,” he noted.
Potential connections to gut health and early performance
One area of growing interest is whether an enterotropic ND vaccine might support gut integrity, gut maturation, and even early growth. While the science is still evolving, Hofacre said the concept is biologically plausible.
“When you stimulate the gut the right way, it can help maintain gut integrity,” he said. “And we know that a healthy gut means healthier birds overall — better nutrient absorption, better resilience.”
Studies in young chicks have hinted at improved weight gain or feed conversion following certain immune-modulating enteric vaccines. Hofacre emphasized that these findings do not indicate a performance additive but rather reflect how immune modulation can support a chick’s natural development.
“If the chick feels good, eats well, and gets off to a strong start, you’re going to see that reflected in growth,” he said.
As research expands, some investigators are also examining how gut-associated stimulation might affect the bird’s ability to handle common challenges such as coccidiosis.
“There’s interest in whether activating the gut immune system early may help birds better respond when they encounter coccidia,” Hofacre said. “We’re not saying it replaces anticoccidials or vaccines, but it might support the bird’s overall readiness.”
Compatibility with broader respiratory and enteric programs
Because VG/GA is minimally reactive, integrators have paired it with increasingly complex day-old vaccination schedules. Hofacre said the strain’s gentle profile has allowed it to coexist with live bronchitis vaccines, coccidiosis vaccines, and other components of modern hatchery programs without overwhelming the bird.
“In today’s hatcheries, chicks may receive several vaccines before they leave,” he said. “Using something that doesn’t add stress is critical.”
He added that the enterotropic nature of VG/GA is especially useful when producers administer multiple respiratory vaccines by spray.
“If you’re spraying multiple respiratory vaccines, the last thing you want is another respiratory hit,” he said. “That’s where a gut-replicating Newcastle vaccine makes a lot of sense.”
Continuing to understand how enterotropic vaccines work
Even as understanding deepens, Hofacre said the industry is still working to understand exactly how enterotropic Newcastle vaccines exert their effects inside the bird.
“There’s still a lot we don’t know about how these gut-replicating vaccines stimulate the immune system,” he said. “We haven’t fully defined what all is happening in the intestine and how that influences the bird as it develops.”
He emphasized that the first days of a chick’s life remain a critical window — one in which vaccination, nutrition, and early management all shape long-term health. Understanding how enterotropic vaccines interact with that early immune environment is an area he believes warrants more attention.
“The first week is so important,” Hofacre said. “Anything we can learn about how vaccines influence the chick in that period is really valuable.”
A broader view of Newcastle vaccination
While Newcastle disease remains largely controlled in commercial U.S. poultry, the risk of virulent strains entering via backyard flocks or international movement persists. For Hofacre, the role of ND vaccines therefore remains fundamental — but the industry’s understanding of what these vaccines can contribute is evolving.
“We’ve always valued vaccines like VG/GA because they protect birds without slowing them down,” he said. “Now we’re starting to see they may have additional benefits we didn’t fully appreciate.”
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