Coccidiosis control is important to every poultry production system, but managing the available options can be a somewhat fluid process. While there are a range of choices, each one has its own set of pros and cons.
“How do you decide whether to use a drug versus vaccine; an antibiotic or no antibiotic; an attenuated or non-attenuated vaccine?” is a question Greg Mathis, PhD, coccidiosis specialist with Southern Poultry Feed & Research Inc., posed to attendees of the 2024 Poultry Science Association meeting.
“I would ask: What is the season? What is the bird weight? What is the stocking density? There are so many things to consider.”
In his presentation, Mathis outlined considerations for the FDA-approved drugs and USDA-approved vaccines available for coccidiosis control within US flocks.
Long-standing anticoccidials
There are 12 FDA-approved anticoccidial drugs available in the US today, and on average, they are at least 60 years old. In fact, zoalene, recently the No. 1 anticoccidial used in the US, came to the market in the early 1960s. “Thanks to the poultry industry’s long-term planning which utilizes rotation and shuttle programs, these drugs are still effective,” Mathis said.
The 1970s saw a host of ionophores approved for anticoccidial use, including monensin, lasalocid, salinomycin and narasin. As soon as the ionophores were approved they quickly became the predominantly used anticoccidial. “Because of ionophores’ unique efficacy, at times almost 100% of the market used them.”
There are many reasons why no new anticoccidial drugs have come to market. One is because ionophores’ effectiveness tempered the development of new anticoccidials, he noted. Another reason is due to FDA regulation changes in the 1990s, which made the approval process too long and expensive for companies to bring new anticoccidials to the market.
Two categories
Anticoccidial drugs are divided into two categories: polyether ionophore antibiotics and chemical synthetics.
“The polyether ionophore antibiotics are antibiotics; there’s no two ways about it,” Mathis said. “But their removal for antibiotic resistance is not applicable because they are not used in human medicine.” However, he noted, they cannot be used in no-antibiotics-ever programs.
There are five ionophores, and their greatest asset is a broad spectrum of activity, but they do not fully control the coccidia. “It’s more of a moderate control,” he noted, “which allows the coccidia to cycle through birds so it has a direct effect and an immunological effect, combining to make a powerful control program.”
For coccidiosis control, the ionophores are further divided into two categories:
- Monovalents, which include monensin, salinomycin and narasin. “These are strong against Eimeria acervulina but not particularly strong against tenella, the cecal parasite,” Mathis said.
- A divalent, which is lasalocid. It is stronger against tenella but not E. acervulina. “So, there are differences, and yes, there is some cross-resistance between all of them. However, there is less cross-resistance between categories,” he added.
Therefore, when using a strict ionophore program, the approach is to shift from a monovalent to a divalent or a divalent to a monovalent to change the mode of action and reduce resistance development.
“Originally, we thought there would be little chance of developing resistance to ionophores because of the direct and immunological control,” Mathis pointed out. “There was not a lot of direct pressure, and the mode of action further limited it. However, extensive ionophore usage, sometimes reaching nearly 100% of the market, resulted in significant decreased sensitivity.”
Chemical options
There are seven chemical options, and they generally have a strong efficacy with a broad spectrum of activity. One exception is amprolium, which works best against E. tenella but has limited activity against E. acervulina or E. maxima.
Diclazuril is considered one of the stronger anticoccidials. “If sensitive, it will almost completely kill the coccidia,” Mathis said. “There are few oocysts passed if there’s full sensitivity, making diclazuril a great option for a cleanout program. Cleanout programs reduce oocyst load, which can be beneficial for subsequent vaccination programs.”
One drawback is that diclazuril does not work against E. maxima asexual stages, and those are the lesion-forming stages which cause the damage. “It works against sexual stages, so it does not kill off the oocysts,” he noted. “This E. maxima issue can potentially increase the chance of necrotic enteritis.”
It’s notable that all anticoccidials can develop resistance to some degree. But the stronger the chemical, the more selection pressure, thus the higher the potential for resistance to develop.
“Remember — these seven chemicals have no antimicrobial activity, so they can be used in ‘never-ever-antibiotics’ or ‘without-antibiotics’ production. We have relied on these tremendously in recent years because of consumer pressures on the end product,” Mathis said.
One combination
Although there are combination options for use elsewhere in the world, the US has just one anticoccidial combination available. It is a combination of low levels of nicarbazin and narasin. This combination produces a synergistic activity. “The synergy of these make them stronger when used together rather than separately,” Mathis noted. One advantage of a combination is the reduced toxicity by using lower levels of each drug. Other advantages are: The combination provides two different modes of action and has efficacy against different coccidia life-cycle stages.
Rotation and shuttle programs
Ionophores generally have a similar mode of action against coccidia, whereas each chemical has a different mode of action. Therefore, a strain that develops decreased sensitivity to an ionophore may be controlled by a chemical, and vice versa. This has allowed anticoccidials to remain effective.
The poultry industry has taken advantage of this by adopting rotation and shuttle programs.
A shuttle program changes drugs within a growout period. So, one drug is used in the starter feed, then it changes to another type for the grower diet. In a rotation program, the anticoccidial changes between growouts. Thus, successive flocks receive different drugs, providing different modes of action against different coccidia species and strains at different stages to eliminate continuous pressure.
Most poultry producers use both programs to achieve sustainable coccidiosis control.
Vaccine momentum
Vaccine use has increased over the years, largely due to growing pressure on antibiotics and the fact that there are only 12 anticoccidials available. “In the summertime, 70% of the birds or higher are vaccinated. It became a trend to use vaccines in one cycle, then go on to something else,” Mathis noted. Today the trend is to vaccinate more than one cycle. Multiple flock vaccinations can lead to an environment that is a population of predominately vaccine strains, which is often advantageous.
Vaccines come in the form of attenuated, nonattenuated and a combination. They are often administered on day of hatch, using spray cabinets to apply a water-based or gel-based vaccine. The birds preen off the droplets and consume the vaccine.
To increase vaccine coverage, spraying vaccine on starter-feed trays as a secondary application is gaining traction, Mathis pointed out.
All vaccines contain E. acervulina, E. maxima and E. tenella, with immunity building stronger with each 7-day lifecycle. “You can pick up 14-day-old birds, challenge them and find a linear immunological response each week, with very strong immunity by day 35,” he noted. “That immunity will not wane for a 60- or 70-day-old bird. Once established, immunity should hold until the birds are marketed. Therefore, you should not get a late effect of coccidia that sometimes occurs with anticoccidial drugs.”
Mathis cited other pros to vaccines, including that no new drugs are coming to market. Also, there are no resistance or sensitivity issues. “Vaccines are antibiotic-free, drug-free and there are no residues or withdrawal times. So, vaccines provide increased production flexibility,” he said.
Vaccines can replace a drug’s coccidia strains, providing a break to lessen the risk of declining sensitivity. They also produce solid immunity against all strains contained in the vaccine. “Probably one of the best selling points is that the coccidia strains are less pathogenic than wild strains,” Mathis noted. “Every vaccine has differences in pathogenicity, but each and every one is less pathogenic than the wild strains.”
Of course, there are house-management practices that influence vaccination outcome, along with vaccine viability, storage and application.
Although there is no one solution to long-term coccidiosis control, there are many options available to producers. Designing a flexible plan that utilizes the right option at the right time can allow for the greatest outcomes.
