By Philip A. Stayer, DVM, MS, ACPV
Dr. Phil Stayer Poultry Consulting, LLC
Hattiesburg, Mississippi, USA
Coccidiosis-control program planning is essential to maintain flock health and performance using the limited tools available in US commercial poultry production. In particular, ionophores are part of the veterinary tool chest to counter the ever-present coccidiosis challenge.
For poultry producers who have not used ionophores in a while, it is worth looking into the history of ionophores; some of the historical lessons learned from years of their commercial use still apply. It is also helpful to review the current practices of ionophore use.
The history
Ionophores have traditionally been used in poultry feed to control Eimeria spp. infestations, along with 3-Nitro (Roxarsone), an arsenical that potentiated anti-coccidial effects of the ionophores, as well as in-feed gram-positive antibiotics, to keep ubiquitous Clostridium spp. at bay. The ionophores have enjoyed the longest period of use within a year and year-to-year due to the slow onset of anticoccidial resistance.
Before coccidiosis vaccines became popular, ionophores were used alone in “straight” programs (the same product from day of placement until harvest) for most of the year, and “chemical-ionophore shuttles” (two in-feed products are used within the same flock at different ages) during the cool months.
As coccidiosis vaccines gained ground, ionophores shared the warmer seasons with the vaccines. Eventually, without the aid of 3-Nitro, ionophores performed better when used in conjunction with coccidiosis vaccines.
Usage practices
All currently available ionophores in the US have a dose range to accommodate different regions, seasons and objectives for coccidiosis control. Higher doses are typically required with higher parasitic challenges associated with cooler weather (accumulated in-house moisture) and mid-life of the broilers (21 to 35 days of age).
For most seasons of the year, ionophores are used alone to control coccidiosis in straight programs, perhaps altering dosages as coccidiosis challenges change with age.
In wintertime, grower and finisher feeds with ionophores frequently follow earlier starter feeds with non-ionophorous compounds, traditionally called chemicals. Compared to ionophores, non-ionophores allow less coccidiosis cycling, called “leakage,” which simply means evident coccidiosis presence even while using an efficacious anticoccidial. These wintertime shuttle programs are favorable because coccidiosis challenges are more severe with moist litter associated with cool-weather ventilation.
The practice of using ionophores with coccidiosis vaccines is called “bio-shuttle,” which mimics the verbiage of the chemical-ionophore shuttle. Because the ionophores don’t kill all the sensitive oocysts present in a population, some of the vaccine oocysts persist to continue stimulating host immunity.
The ionophore may simply reduce the severity of the coccidiosis cycling within flock members that missed vaccine uptake on first exposure and, later in age, are dealing with excessive oocyst challenges shed from vaccinated flock mates.
Impact on gangrenous dermatitis
All ionophores inhibit clostridial growth, which helps lessen necrotic enteritis, but may increase the likelihood of gangrenous dermatitis. Thus, ionophore use may be limited due to increased gangrenous dermatitis risk during certain seasons in certain regions.
For example, regions with higher water tables, like North Carolina or the Eastern Shore, may face prolonged clostridial challenges compared to drier regions such as east Texas and California. All regions tend to accumulate litter moisture during cooler weather, so dermatitis challenges increase in almost every poultry-growing area throughout the winter into spring.
The benefit of ionophores for necrotic enteritis is straightforward: Drug (ionophore) versus bug (bacteria) keeps the bug from hurting the host. The increased risk of gangrenous dermatitis, however, is less understood.
One theory is that ionophores force Clostridium spp. into spore form, and the smaller spores are more easily translocated across the intestinal barrier than larger vegetative forms. Circulating Clostridium spores then lodge in disrupted capillaries, usually in a bruise after tissue damage, and start to grow rapidly in the nutrient-rich, anaerobic environment this family of bacteria prefers, producing gangrenous dermatitis lesions.
Gangrenous dermatitis is the clinical manifestation of subcutaneous clostridial disease. Ionophores impact clostridial diseases to some extent, but both necrotic enteritis and gangrenous dermatitis may occur in a flock regardless of ionophore use due to other factors.
Fecal water, feed refusal
Ionophores all share the same mode of action — disrupt membranes to create ionic imbalances — but each separate product has its own unique chemical formulation and unique side effects.
For example, some ionophores require a special ionic feed balance to prevent excessive fecal water. Also, most ionophores are apparently bitter to birds, so with elevated inclusion levels, birds may consume less feed; this is evident more so with some ionophores than others.
An ionophore that induces wet feces is contraindicated in cooler weather, while an ionophore that causes feed refusal would not be preferred in hotter weather.
Cross-resistance, sensitivity testing
In my experience, ionophores do not create cross-resistance with other ionophores, but resistance will occur with prolonged use of any single ionophore. Manufacturers recommend rotating products within a year to maintain the longevity of the total anticoccidial portfolio.
Although anticoccidial sensitivity tests (AST) in battery cages do not represent the true coccidiosis challenge or total anticoccidial efficacy of the products tested, they may provide insight into relative efficacy within the ionophore class to particular coccidia isolates. ASTs also help find the most effective ionophore for a specific location or region, provided that all ionophore products are readily available to the producer.
Rise of phytochemicals
With non-antibiotic marketing strategies, other products have taken precedence over ionophores.
For example, many plant-derived products, mainly of the saponin class but also herbal and tannin extracts, demonstrate coccidiosis control somewhat less than ionophores or other synthetic anticoccidials. These phytochemicals have been successful in tempering flock coccidiosis-vaccine responses, perhaps more so than outright replacement of in-feed anticoccidials.
Phytochemicals may be used in conjunction with any of the anticoccidials, ionophore or otherwise, much like how 3-Nitro was used when it was available in the US. As with 3-Nitro, producers should expect an economic return when adding any of these non-nutritive feed additives to their poultry diets.
Final thoughts
As the US poultry industry moves back to using more of the FDA-approved commercially available anticoccidial products, ionophores may regain their large part of the anticoccidial market share.
Ionophores continue to be an efficacious and relatively cost-effective means to control coccidiosis. Wise use of the ionophores as part of the anticoccidial program planning should ensure their benefits for the foreseeable future in US commercial poultry production.
Editor’s note: The opinions and/or recommendations presented in this article belong to the author and are not necessarily shared by Modern Poultry.
