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Keeping up with coccidiosis remains challenging

12 October 2021, at 11:59am

I’ve been learning about coccidiosis ever since graduate school, back in 1990. In fact, my master’s thesis was about coccidiosis in broilers. I wrote 150 pages about chicken poop.

In the ensuing 30 years, I’ve dealt a lot with coccidiosis, and it’s been an interesting journey. One thing is for sure — there’s always more to learn, and keeping up with this ubiquitous disease remains challenging.

Like most production veterinarians, I’ve used ionophores, which weaken coccidial cell walls, thus directly affecting the parasite. Some infection with ionophores, colloquially called “leakage,” is expected, but it’s not an overwhelming infection. Limited exposure allows the birds’ intestines to interact with the parasite, which initiates host immunity.

In contrast, non-ionophore anticoccidials work inside the parasite’s cells while the coccidia themselves are replicating within the host tissue. This type of anticoccidial, if effective, keeps coccidial infections at levels low enough to prevent a significant immune response. Generally speaking, ionophores tend to maintain efficacy for longer periods of time compared to non-ionophore anticoccidials since they induce immunity, but there are always exceptions to this simple rule.

Unforeseen consequences

During my first years in production medicine, a range of anticoccidials were used and rotated with the seasons in an attempt to reduce resistance, maintain product efficacy and minimize flock parasitism. I’ll readily admit that despite careful monitoring of flock health status, I made some changes along the way that I thought were good plans for coccidiosis control only to end up scrapping the plan because it wasn’t working. There was either a clinical coccidiosis outbreak or poor feed efficiency.

Typically, I used a non-ionophore anticoccidial in cold weather when the coccidiosis challenges rose due to increased litter moisture. Ionophores were used to complement the non-ionophore anticoccidials. We’d start with a non-ionophore anticoccidial during the starter phase, then switch to an ionophore during the grower and finisher periods. In warmer, drier weather, however, we’d use ionophores exclusively from placement to harvest.

I’ve also used coccidiosis vaccines. They deliver populations of various species of Eimeria at formulated doses that actually cause a limited parasitic infection so the chickens develop immunity without clinical disease. There are various formulations of commercial coccidiosis vaccines available in the US; all of them contain at least the three Eimeria species that most often cause coccidiosis in broilers: E. acervulina, E. maxima and E. tenella.

Coccidiosis vaccines are delivered either directly into the embryonated egg prior to hatch or sprayed on the chicks at day of hatch. Regardless of the application technology, chicks must consume sporulated oocysts for any of the vaccines to be efficacious. Simply seeing the dye added to the vaccine on the chicks’ backs or in their mouths when the vaccine is sprayed on does not mean every chick received an effective dose, although most vaccines can claim over 90% uptake.

Weather affects vaccine timing

My use of coccidiosis vaccines has generally been limited to summer months due to necessary flock management. Young birds need to scatter throughout the house before heavy doses of oocysts accumulate in the brooding region, which is easier to do in warm versus cool weather. Flocks on either anticoccidials or vaccines benefited from non-specific intestinal support provided by arsenicals like 3-nitro and Gram-positive antibiotics.

For several years I tried using coccidiosis vaccines without anticoccidials but found flock health was just not as good as it was when vaccination was followed by an anticoccidial — though not before 14 days of age since that risks killing off the vaccinal oocysts that stimulate immunity.

I also found that after vaccination, 3-nitro was just as effective as using an in-feed anticoccidial. When 3-nitro was removed from the marketplace, it was a struggle to find a replacement quite as effective, although various in-feed anticoccidials were a close run-up.

Bioshuttle program favored

Today, the combination of vaccination followed by various anticoccidials — often called a “bioshuttle” program — remains a favored program among conventional broiler producers. Interestingly, I’ve found that higher doses of ionophores are necessary to accomplish the same degree of coccidiosis control as lower doses with 3-nitro. I don’t know why but perhaps 3-nitro provided ancillary support for coccidiosis control that we didn’t appreciate until it was removed from the market. To regain flock health back to former levels, it now appears that both coccidiosis vaccination along with higher ionophore doses are necessary. That’s based on intestinal lesion scores and flock performance.

Theoretically, coccidiosis vaccines initiate subclinical infections that induce immunity while in-feed anticoccidials treat birds in the flock that did not get vaccinated at day of age. An effective dose of any species of Eimeria will result in increased oocyst shed. If a chicken is missed at day-of-age vaccination, the next coccidiosis exposure may be 10 or even 100 times higher if the naïve bird consumes the feces of flock mates that were properly vaccinated.

Younger birds appear more resistant to a coccidial challenge than older, naïve birds, perhaps due to limited intestinal mucosal surface for parasite proliferation. Later in growout, a higher dose of coccidial oocysts and more intestinal geography places those missed flockmates at higher risk for clinical coccidiosis than birds that were vaccinated in the hatchery. Using an anticoccidial — particularly an ionophore — helps limit the damage to chickens that are exposed later in life to elevated oocyst counts

Current recommendation

My current recommendation for coccidiosis control is to utilize the range of anticoccidial tools available. Practically speaking, this means use of a coccidiosis vaccine applied in ovo or sprayed on day-of-age birds followed with an in-feed anticoccidial. Coccidiosis vaccines should be used at the recommended dosage to get optimal results. Anticoccidials in feed should be used at the lowest effective dose, but they may have dose ranges that allow increases and decreases as needed based on flock health monitoring.

At Sanderson Farms, we’ve been successful using bioshuttle programs across several climatic zones and seasons, even year-long, and we’ve not seen any problem with anticoccidial resistance.

Coccidiosis is arguably the most expensive pathogen for commercial broiler production since it’s an intestinal disease that directly affects feed utilization, and feed is the major expense that comes with producing live chickens. Looking back over the years, the major change affecting coccidiosis control is the loss of effective tools. For conventional systems, it’s the loss of 3-nitro. For no-antibiotics-ever systems, it’s the prohibition on using ionophores, since they’re considered antibiotics by FDA.

Otherwise there haven’t been a lot of changes since there has been a dearth of new anticoccidials. It will be interesting to see in the decades ahead if there are any significant changes to the way coccidiosis is managed.