Ionophore status change would threaten bird health, sustainability, veterinarian warns

An interview with Daniel Parker, VetMB, CertPMP, Slate Hall Veterinary Practice

Q: Why are some scientists in Europe calling on legislators to reclassify ionophores as antibiotics?

DP: In Europe, ionophore coccidiostats are currently classified as antimicrobials and are registered for use as feed additives. However, some scientists believe that they should be considered antibiotics — as they already are in the US — and, in Europe, registered for use as veterinary medicines rather than feed additives. But there are also a number of important differences between ionophores and antibiotics used in human medicine that are worth noting.

Q: How do ionophores and antibiotics differ?

DP: The first thing to clarify is that ionophores are not used in human medicine. They are not even used in chickens to treat bacterial disease; they are used as antiparasitics to manage coccidia, the family of protozoan parasites that cause coccidiosis.

Resistance to antibiotic compounds such as beta-lactams is usually associated with a single gene or point mutation in the bacteria. By contrast, developing resistance to ionophores would require multiple gene mutations, making this far less likely to occur.

Q: Should ionophores be reclassified as antibiotics, what would be the practical implications for how they’re obtained and used?

DP: If ionophore coccidiostats were to be reclassified as veterinary medicines then they could only be prescribed by a veterinarian following diagnosis of disease. Ionophore coccidiostats have to be used prophylactically in feed as they work by moderating the replication of the parasite in the gut and therefore control the overall parasitic challenge. Once disease is diagnosed it is too late to treat using ionophore coccidiostats, and they would be ineffective.

Q: How would reducing or removing ionophores affect poultry health and welfare?

DP: The most concerning impact — from health, welfare and economic standpoints — would be an impact on intestinal health and probably an increase in mortality rates. In the US, where ionophores are classified as antibiotics, they’ve removed all ionophores from the diets of those birds that are produced in no-antibiotics-ever systems, and if you look at the data, the mortality rates in these systems are higher than in conventional systems.

Another probable consequence would be increased use of therapeutic antibiotics. Coccidiosis predisposes chickens to other problems, such as clostridial bacterial infections, which can lead to necrotic enteritis. These diseases not only cause animal suffering and performance losses, but they also often require treatment with antibiotics that may be more likely to be important to human medicine. So removing ionophores would be counterproductive on several fronts.

Q: You mentioned that reducing or removing ionophores would bring about economic losses. How much are we talking about?

DP: To assess the economic impact on the UK poultry industry, we combined two established models that looked at different scenarios of ionophore reduction, finding costs per bird would likely increase by between 3.3% and 10.8%. This amounts to between £68.02 million to £109.95 million (approximately US $94 million to $152 million).

Q: Your paper also claims that reclassifying ionophores as antibiotics would have negative environmental impacts. Can you elaborate?

DP: Climate change is probably the biggest challenge facing society, and for that reason we all need to consider sustainability in our food production. There is no question that ionophores improve sustainability by effectively controlling coccidiosis, thereby improving gut integrity and helping the bird grow more efficiently.

Without ionophores, producers would need to rear fewer birds per house to control disease, resulting in higher annual carbon emissions for the same amount of meat. In our paper, we refer to models showing that removing or reducing ionophores would result in the production of an additional 84,000 tons of CO₂ equivalent per year.

Q: Is vaccination a viable alternative for the control of coccidiosis?

DP: Vaccines are used extensively in the commercial layer sector and in the broiler breeder sector. But for the shorter-lived broiler, there isn’t the time in the bird’s life to fully develop that immune response, and the challenge to the broiler comes very early in its life. So while vaccines still have a place in poultry production, they are best used as part of an anticoccidial control program that also includes ionophores and chemical anticoccidials.

Q: Since you don’t support reclassifying ionophore coccidiostats as veterinary medicines, do you believe any alternative legislation is needed to ensure responsible use?

DP: I believe that ionophores are already sufficiently regulated under the feed additives legislation, which is very comprehensive in its own right. Feed additives have to undergo a rigorous registration process before approval, and feed mills have to comply with strict regulations to be allowed to incorporate the feed additives into poultry diets.

Q: There’s more to coccidiosis control than just ionophores. What other measures can producers take to manage the issue, and do you see approaches changing in the future?

DP: The first priority should be reducing the parasitic challenge to birds with robust hygiene and biosecurity. Rotation of the armory of products for control of coccidiosis is also needed to preserve their effectiveness. This is especially important for the chemical coccidiostats, as coccidia can rapidly develop resistance to these products if they are used continuously.

The bottom line is that this disease is caused by a parasite, and these highly successful parasites have developed over the years to become adapted to their host. There’s only so much good management, hygiene and biosecurity can do to control this well-adapted parasite. We have a limited range of tools available to control coccidiosis, but the good news is we know that ionophore coccidiostats are still highly effective when used responsibly.