Coccidiosis-control programs meet at the Broiler Bar

By Manuel Da Costa, DVM, PhD, Director of strategy and innovation, Cargill

Three coccidiosis programs meet at the Broiler Bar. At first glance, this might sound like a story about coworkers unwinding after hours, sharing a drink to relieve the daily pressure of safeguarding broiler gut health. Instead, this is the story of how they are called before the Bar — not for refreshments but for judgment. Each program must now prove whether it meets the bar for gut health performance, or whether it stands accused as a potential accomplice in the rising incidence of two pathogenic Enterococcus strains: E. cecorum and E. faecalis.

All of the suspects are present: the Chemical (zoalene), the Ionophore (narasin) and the Vaccine (coccidiosis live vaccine). Each stands accused of potentially abetting the proliferation of pathogens. As the proceedings begin, a unique character observes in the corner: Biostrong^™ Dual (postbiotic and essential oil nucleos combination), not a judge or jury but a mediator, trying to keep the peace. The stage is set for a courtroom drama of microbes and management, where science serves as the forensic evidence.

The case: a pathogen on the rise

Pathogenic Enterococcus strains have been creeping into poultry operations, causing disease and losses — a criminal offense in the poultry world. These bacteria can exploit weaknesses in the gut’s defenses, translocating from the intestines to other organs and wreaking havoc.

The court wants to know: Have the coccidiosis-control programs inadvertently created an environment for this microbial menace?

Each program has a motive of sorts. Coccidiosis, caused by Eimeria parasites, is a common threat, and how we control it might influence the gut ecosystem in different ways.

To crack the case, evidence from a recent 42-day broiler trial is presented. In this trial, broilers were raised under three coccidiosis-control regimens — chemical, ionophore and vaccine — each either with or without Biostrong Dual added to their feed.

Importantly, the flock faced a mild Enterococcus challenge under natural conditions — in other words, the pathogen was present in the environment, lurking for an opportunity. Samples were collected via cloacal swabs throughout the trial, and splenic cultures were performed. Performance metrics were also assessed. Additionally, the microbiome-analysis tool, Galleon™, provided forensic insight into bacterial populations. With data in hand, the trial begins.

Suspect #1: Chemical takes the stand

Zoalene, a venerable chemical coccidiostat, steps up first. Zoalene prides itself on being a non-antibiotic anticoccidial that protects birds from coccidiosis by directly inhibiting Eimeria parasites in the gut, preventing those costly coccidial lesions. On the surface, the Chemical defense seems straightforward: “I just do my job controlling coccidia and preventing coccidia,” it says. And indeed, under the Chemical’s program, birds avoided coccidial damage and showed the lowest E. maxima cycling (microscores) at 19 days.

However, the cross-examination reveals a twist. The Galleon microbiome forensics report shows that chicks on the Chemical program had a slower-developing gut microbiome than those on the other programs. By day 35, these birds showed the lowest levels of short-chain fatty acid (SCFA)-producing bacteria, indicating that their cecal microbiota was the least mature of the three programs. SCFA producers, like those that generate butyrate, signal a healthy, developed hindgut flora — the higher their presence, the more “mature” and stable the gut ecosystem.

Said plainly, Chemical’s approach kept coccidia at bay but seemed to delay the gut’s microbial maturation.

Was this delay harmful? Possibly. A less mature microbiome might mean fewer beneficial metabolites early on. Yet, mysteriously, when it comes to the “crime” at hand, Chemical’s flocks didn’t suffer the worst of the Enterococcus prevalence. The evidence shows a relatively low prevalence of pathogenic Enterococcus in the Chemical group.

At day 35, only about 17% of birds on the Chemical program tested positive for pathogenic  Enterococcus in their organs, a level on par with the Vaccine group and much lower than the Ionophore group. In other words, Enterococcus wasn’t running rampant in Chemical’s section of the flock.

The prosecution notes that Biostrong Dual had little effect on Enterococcus prevalence in this case, even though it supported the birds’ efficiency, as evidenced by lower feed-conversion rates (FCR), especially when working with Chemicals.

The Chemical program rests its case: It may slow microbiome development, but it kept coccidiosis under control and didn’t particularly fuel the Enterococcus fire while showing best performance when combined with Biostrong Dual.

Suspect #2: Ionophore in the hot seat

Next up is narasin, the Ionophore. Narasin’s coccidiosis-control method is subtler than the Chemical’s. Ionophores work by disrupting ion gradients in parasite and bacterial cell membranes, serving as the “bar bouncer” that makes the gut environment selective for certain organisms.

The Ionophore testifies confidently about its track record: Ionophores have been mainstays in broiler production, valued for improving feed efficiency while keeping coccidia largely in check. Unlike Chemicals, Ionophores do have antibacterial side effects: They tend to target many gram-positive bacteria in the gut.

It is this side effect that the prosecution probes. The microbiome forensic data reveal that in the first week of the trial, chicks on the Ionophore program showed a notable drop in beneficial Lactobacillus levels, especially compared to other programs. Typically, Biostrong Dual is observed to increase lactate-producing bacteria such as Lactobacillus in young chicks, a sign of a good start for gut health.

But Ionophore’s presence was an exception: This Ionophore strongly suppressed Lactobacillus early on, even with Biostrong Dual in the diet. Lactobacilli are important “good guys” that produce lactic acid, lower gut pH and crowd out unwelcome microbes in the first days of life. By knocking them back, Ionophore may have inadvertently created some space in the microbial ecosystem — a potential opening for opportunists like Enterococcus.

As the trial progresses to later flock ages, the case against Ionophore thickens. At day 35, the birds on the Ionophore program without Biostrong Dual had the highest rate of pathogenic Enterococcus among the groups. A full 33.3% of Ionophore-only birds harbored pathogenic Enterococcus in their organs — double the incidence seen in the Chemical or Vaccine groups.

The “crime” clearly spiked under Ionphore’s watch. However, when Biostrong Dual was added to Ionophore’s program, the story changed dramatically: Pathogenic Enterococcus positives dropped to just 8.3%. The forensic evidence is stark: With Biostrong Dual present, the Ionophore group went from the worst Enterococcus problem to virtually none by day 35.

It appears that Biostrong Dual acted like Ionophore’s much-needed partner on the force, restoring order by accelerating beneficial microbiota and possibly compensating for Ionophore’s collateral damage. Performance data back this partnership, too: Across all programs, Biostrong Dual improved FCR significantly, by roughly 2 to 3 points on average. In short, with the “mediator” (Biostrong Dual) on duty, Ionophore’s flocks converted feed more efficiently and kept bad bugs at bay.

Ionophore, now sweating a bit, asserts that it never intended to help Enterococcus. Its goal was coccidiosis control and improved growth, which it indeed does in broilers. The judge nods, acknowledging that Ionophore did hold coccidiosis in check and that its birds, when aided by Biostrong Dual, thrived with minimal pathogens. But the unintentional consequences on the microbiota in the absence of that aid have been duly noted in the court record.

Suspect #3: Vaccine on trial

Finally, the spotlight turns to the live coccidiosis vaccine. Vaccine confidently strides to the stand. Its strategy is unique: “I infect the birds — for their own good.” A live vaccine containing several strains of Eimeria is given to day-old chicks, seeding a controlled coccidial infection to stimulate the birds’ immunity.

Over the next few weeks, the vaccinated birds cycle these mild infections and develop immunity to coccidiosis, effectively disarming the parasite threat in the long term. Many producers rotate vaccines into their programs to reset or reduce drug use, delivering good performance when managed correctly.

The court inquires, “How does this live vaccine approach affect the gut microbiome and our villain, Enterococcus?” The forensic microbiome data reveal a fascinating outcome: The Vaccine program’s microbiome matured the fastest of all. By day 35, birds in the Vaccine group had the highest levels of SCFA-producing bacteria, followed by the Ionophore group, then the Chemical; in other words, Vaccine > Ionophore > Chemical in terms of microbiota-maturity ranking.

The Vaccine’s controlled Eimeria exposure seems to have kick-started the gut microbial community. Perhaps the mild gut challenge early on created an environment for fiber-fermenting, butyrate-producing bacteria to flourish by grow-out time. These SCFA producers contribute to gut health by fueling gut cells and lowering inflammation, acting as a marker of a well-developed gut ecosystem. Thus, in microbial terms, Vaccine might say that it rehabilitated the gut neighborhood, training it to be resilient.

Yet, Vaccine’s approach is a double-edged sword. During the first couple of weeks, as the vaccine strains cycle, there is a low-level gut infection occurring, a bit of controlled chaos. This can cause mild intestinal irritation and must be managed with good litter and feed support.

It’s in that early window that Enterococcus may try to break and enter. The evidence shows that without Biostrong Dual, the Vaccine group experienced some pathogenic Enterococcus issues: At day 19, vaccinated birds (no Biostrong Dual) had ~16.7% incidence of pathogenic Enterococcus, similar to the Ionophore group at that age. By day 35, the Vaccine-only group still had about 16.7% of birds positive for pathogenic strains.

So, although the Vaccine program ultimately cultivated a diverse microbiome, it wasn’t immune to Enterococcus’s sneak attacks early on.

When combined with Biostrong Dual, the Vaccine program’s weak spot is reinforced. With Biostrong Dual in the diet, the Vaccine group had its pathogenic Enterococcus cut in half (down to 8.3% of birds at day 35), and overall Enterococcus presence was also lower (50% of birds versus 66.7% without Biostrong Dual).

Biostrong Dual postbiotics and essential oils seemed to hasten the gut’s stabilization, ensuring that the beneficial microbes established even earlier and produced compounds that suppressed opportunists. Indeed, by day 7, the Biostrong Dual-supplemented birds already had more lactate producers, such as Lactobacillus, in their intestines, a sign that Biostrong Dual sped up microbiome development from the start.

In the Vaccine’s case, this likely helped chicks cope with the Vaccine’s challenge more effectively — less “collateral damage” for Enterococcus to exploit. The feed-conversion improvements were seen here, too: The Vaccine-program birds gained a feed efficiency edge with Biostrong Dual on board. It is as if Vaccine and Biostrong Dual together formed a one-two punch: One builds immunity and gut maturity, and the other maintains order and efficiency during the process.

Exhibit A: Biostrong Dual, the mediator

Throughout the testimonies, Biostrong Dual has been a recurring character. What exactly is this product, and why does it keep appearing like the trusty mediator in each suspect’s narrative?

Biostrong Dual is a feed additive that combines two categories of nutritional “good guys”: a postbiotic derived from Saccharomyces cerevisiae yeast fermentation, and a blend of essential oil compounds. It is a combination of beneficial microbial metabolites and plant extracts designed to support gut health in broilers. The postbiotic component can modulate the hindgut microbiota, fueling beneficial species and fortifying the gut barrier, while the essential oils support intake and primarily act in the upper gut to improve digestion and feed utilization.

Think of Biostrong Dual as an ecosystem manager in the broiler’s gut: not introducing new microbes but encouraging the right ones to flourish and discouraging the troublemakers.

In our trial, Biostrong Dual served as the mediator. Galleon microbiome analysis confirmed that Biostrong Dual’s presence altered the crime scene: more good bacteria early, faster maturation overall and fewer pathogenic Enterococcus detected as birds aged.

Performance records further show Biostrong Dual improved the flocks’ FCR by about 2.6 points on average — a notable gain in efficiency — across all coccidiosis programs. These improvements were not a one-off. They were consistently observed in the trial and align with results from multiple independent trials in which Biostrong Dual boosted bird weights and reduced FCR by 3 to 4 points by day 42.

In short, whenever this “officer” was on duty, the flock stayed in better shape, growth-wise and microbially.

Biostrong Dual didn’t arrest Enterococcus outright. Birds with Biostrong Dual still had some Enterococcus present, just less unfavorable ones and lower prevalence. Rather, it kept the microbial community balanced enough that opportunistic pathogens had fewer chances to overrun the system.

One could liken it to a traffic cop at a busy intersection, ensuring the beneficial bacteria get the green light to establish early, directing “traffic” so that SCFA producers thrive by mid flock, and waving the red stop sign at pathogenic Enterococcus speeding toward the gut lining. The result is a more orderly gut environment amid the stress of coccidial-control measures, with a delivery of better performance.

Verdict: Best defense is a balanced ecosystem

After weighing all the testimony and evidence, the court delivers its verdict. The rising Enterococcus problem in poultry cannot be pinned squarely on any single coccidiosis-control program.

The suspects are not outright guilty. The Chemical program was perhaps the least implicated in fostering Enterococcus; it kept things calm, though at the cost of a slower-developing microbiome. The Ionophore showed that it could inadvertently tip the scales in favor of Enterococcus by suppressing key good bacteria early on, a lapse that Biostrong Dual effectively corrected. And the Vaccine, while promoting a robust microbiome and immunity in the long run, had a vulnerable window in which Enterococcus could creep in if not supported nutritionally.

In the final analysis, the speed and quality of microbiome maturation emerged as a crucial factor. The faster and more completely a chick’s gut flora reaches a healthy equilibrium, the smaller the chance pathogenic Enterococcus has to proliferate and invade. It is a race between gut maturation and pathogen opportunism. In the flocks on trial, this race often made the difference in outcomes.

In poultry production, maintaining good gut health is a collective effort: Coccidiosis-control programs, nutrition and additives like postbiotics are all important. None of the coccidiosis-control methods intended to aid Enterococcus, but their impacts on the gut ecosystem differed. Those differences set the stage for either microbial balance or chaos.

As the crowd at the Broiler Bar disperses, the case of Enterococcus on trial leaves a lasting lesson. Rather than blaming one coccidiosis-control program or another factor for pathogen problems, we should look at how each influences the succession of gut microbes in a growing bird.

A steady, early establishment of beneficial bacteria appears to be the best defense against Enterococcus playing the villain. In practical terms, that could mean pairing our anticoccidial strategies with gut health support (postbiotics, phytogenics or other tools) to ensure that no space is left for the “bad bugs” to fill.

Case closed? Perhaps for this investigation. But the pursuit of a balanced poultry gut goes on, with science and a bit of creative thinking lighting the way. In this courtroom drama, the verdict is clear: When it comes to gut health, accelerating the growth of the right bacteria is key to keeping opportunistic pathogens under control. The tale told above may be whimsical, but the challenge it addresses is very real, and so are the solutions emerging to tackle it.

References: The data and trial insights in this story are drawn from a 2025 Poultry Science Association abstract by Manuel Da Costa et al. and related field evaluations.