Generating sufficient immunity in young broilers requires a balanced approach to immune stimulation, according to Matthew Jones, DVM, PhD, Southern Poultry Research Group (SPRG).
“Too much immunostimulation may cause unnecessary damage to the host, leading to poor performance,” Jones said. “On the other hand, too little immune stimulation may leave birds inadequately protected. The goal is to optimize resistance to decrease disease and improve performance metrics.”
Jones discussed how to fine-tune the balance between immunity and inflammation in a presentation at the 2025 Poultry Science Association annual meeting.
Building early immunity
Early immune development is the foundation for adequate resistance, and it begins in the egg. Maternal antibodies are among the first line of defense against disease for young broilers.
“Broiler producers have vaccination programs designed to help parents and the offspring by enriching eggs with protective, maternal-derived antibodies for the first few weeks of life,” Jones explained.
This initial protection is especially important when chicks are placed on reused litter. “Following placement, these chicks are exposed to a plethora of viral, bacterial and protozoal organisms,” he said. “They are exposed to pathogens early and need to be protected.”
After 2 weeks or less of protection, these mother-derived antibodies begin to wane. Birds undergo a transition and start developing their own antibodies to resist disease. Vaccination programs become pivotal at this time.
Timing pathogen exposures
“We want to frontload the immune system to help broilers develop protection as early as possible,” Jones said. “In broilers, this can be accomplished, in part, with live vaccines. In addition to stimulating innate immunity, some attenuated organisms can linger in the environment and host, allowing broilers to build immunity when their immune system is developed enough to do so.”
Litter also plays a role in early immunostimulation. “Reused litter, which is standard in our practices, gives birds an immunological boost at the very beginning,” he stated.
Research at SPRG and other institutes shows early exposure to bacterial flora not only develops the microbiota but also begins to develop the gastrointestinal tract, Jones added. This expands the impact of reused litter beyond immunological protection to microanatomical changes which support the host.
“We’re trying to establish a microbial ecosystem that will help competitively exclude some of these pathogens, promote intestinal maturation and simultaneously prime the immune system,” he explained.
While this allocation of resources may slow initial growth, if frontloaded, the birds have time to make up from this set back.
Reused-litter research
Research at SPRG demonstrates how birds can leverage this early stimulation to recover from disease. In a trial, chicks were vaccinated with a commercial coccidia vaccine. One group was placed on reused litter from a previous necrotic enteritis outbreak and another on fresh wood shavings.
Both groups were subsequently challenged with pathogenic Eimeria maxima and Clostridium perfringens. On day 14, the birds’ weights were compared.
“As you might expect, we observed significant changes in bodyweight,” Jones said. “Birds placed on reused litter with a pathogenic load had significantly lower bodyweight at 14 days compared to the group placed on fresh pine shavings.”
However, by the end of the research project “the tides had shifted,” he explained. Birds with a primed immune system from the reused litter had only 1% necrotic enteritis mortality. In contrast, the well-performing immune-naive broilers on fresh shavings experienced ~20% necrotic enteritis mortality.
Jones attributes the early exposure to reused litter as a crucial factor in the resistance to the enteric disease.
Timing vaccination, controlling stress
It’s important to consider timing of immunity development and vaccination.
Using coccidia as an example, Jones explained, “We often vaccinate in the hatchery prior to placement. The live coccidia complete the first cycle around 7 to 10 days. A larger spike in oocyst output between 14 and 21 days will follow. This subsequent load is a required stressor to build adequate immunity.”
Like the reused-litter trial, timing around 2 weeks corresponds to the waning of protective maternal antibodies. “As broilers build their own immunity, there is a window of susceptibility,” he added. “I think of this timing like an immunological trough.”
It’s critical to manage other stressors, such as a change in feed phase and form, during this immunological transition. “We don’t want to layer additional stressors at a time when chicks are already stressed and vulnerable,” he said.
“While it is important to activate the immune system, on the other hand, we don’t want ‘too much’ of this immune stimulation,” Jones continued. “Producers should also avoid sustained stimulation. Really strong challenge early can set chicks back so much they are not able to compensate.
“Similarly, chronic infection or one immune-stimulating factor after another can impair growth and slow the birds as they attempt to compensate.
“In conclusion, an orchestrated program that builds immunity and limits the exposure to pathogens is really the avenue to allow the birds to grow and compensate for optimal performance,” Jones said.
