Vaccination has become the preferred method for managing coccidiosis at progressive US broiler operations – not only to avoid drug residues and resistance, but also to improve performance and develop sustainable control programmes.

The editors of Merck Animal Health’s Broiler Health publication talked to two recognised experts on the topic from the company – Charlie Broussard, DVM, and Linnea Newman, DVM – to learn more about their field experiences and discuss new strategies for starting and maintaining successful programmes.

Q. What’s driving the shift from anticoccidial medication to vaccination for coccidiosis control?

CB: There are two major drivers in the US.
The first is gangrenous dermatitis (GD). It’s a significant problem for the US broiler industry, particularly affecting birds over 35 days of age, with highest incidence during the warmer months. GD is associated with the use of ionophore anticoccidials in the grower and finisher feeds of affected flocks. Vaccinated flocks have a dramatically lower incidence.
The other major driver is an increasing coccidiosis challenge, despite the use of anticoccidial medications. The coccidiosis challenge for many complexes, especially small birds, is growing. This growth is due to reduced anticoccidial efficacy, and it is driven by coccidial shedding during the final two weeks of the broiler flock that carries over into the subsequent flock. This “carry–over” coccidiosis challenge puts more and more pressure on the anticoccidial program for each successive flock, reducing the life of the anticoccidial product in rotation.

Q. Can you give an example?

LN: At one US complex producing four-pound birds that was using an anticoccidial rotation programme, the company figured out that it was losing about 1.5 cents per pound (with feed costs at $350 per ton) during the last several weeks that each anticoccidial was used. This was based on analysis over the course of three years. In some instances, the performance loss continued for as much as 12 weeks before the company switched to the next anticoccidial in the rotation. That’s a lot of money lost.
To reduce late coccidial shedding and carryover, a lot of small-bird complexes have begun using zero-withdrawal anticoccidial programs — anticoccidials that do not require withdrawal. The additional expense isn’t always rewarding though, since in-feed anticoccidials with reduced efficacy will still leak. The resulting coccidial shedding and carry-over will still occur and performance will deteriorate.

Q. How do producers maximise coccidiosis control with a vaccine?

LN: The most effective coccidiosis-control strategy is long-term vaccination, but you’ve got to pay attention to environmental influences to get maximum performance from your vaccinated birds.
A live coccidiosis vaccine contains a controlled, balanced dose of Eimeria organisms that stimulate the bird’s natural immunity. In fact, exposing chicks to multiple life cycles of coccidia initiates an immune response that reduces oocyst shedding to almost zero, which is the opposite of the late shedding and the carry-over effect produced by in-feed anticoccidials. Without leakage and carry-over, a poultry house’s Eimeria populations decline over time.

Q. How long does it take for vaccinated birds to build immunity to Eimeria?

CB: Environmental conditions, such as bird density and litter moisture, determine how quickly a full protective response develops. Heat and humidity are necessary for coccidial reproduction. The number of birds will also determine the overall coccidial load.

LN: You need to make adjustments with the seasons:
In the winter, broilers are often held in a partial house for up to 16 days. This typical management strategy will ensure a good build-up of vaccinal oocysts in the litter that will cycle over a short period. If there’s high early stocking density and reduced ventilation, vaccine coccidial populations build very quickly to levels that induce immunity. You need to emphasise control of litter moisture.
In the summer, birds are held in the partial house for a shorter period of time to reduce early bird density. Ventilation should be at maximum. Vaccine coccidia peak later in summer than in winter, inducing immunity by 21 to 28 days of age.
Vaccination provides excellent year-round coccidiosis control if you understand the effect of seasonal poultry-house management on immunity development.

Q. Can in-feed anticoccidials enhance performance in vaccinated flocks?

CB: Yes, and no. The coccidial isolates in Coccivac-B are highly sensitive to all anticoccidial drugs. Roxarsone (3-Nitro) was used in grower feeds to enhance feed conversion in vaccinated flocks, but with Roxarsone off the market, integrators have asked about the use of chemicals or ionophores instead.

LN: When using combination programmes, remember that coccidiosis control comes from the vaccine, not from the feed medication. If the feed medication disrupts the life cycle of the vaccine before immunity is complete, coccidiosis control will fail.
In these situations, where birds have already been vaccinated for coccidiosis, in-feed medication is intended for performance enhancement only. Ionophores are effective antibiotics that provide clostridium control and microflora management. They can be used to maximize performance after the vaccine has induced immunity.

Q. Are there seasonal considerations?

LN: Yes.
In winter flocks, ionophores may be introduced in late grower or finisher feeds to enhance performance after immunity to coccidia is complete.
In summer flocks, lower density may delay the onset of immunity, making finisher feed the logical position for an ionophore. But this is where GD has been associated with ionophore use. Ionophores are not recommended for complexes with GD problems.
This is a key point: the purpose of ionophores in vaccinated flocks is to manage microflora for the purpose of maximising feed conversion. They're not for coccidiosis control and care must be taken to ensure that ionophores do not interfere with vaccine-induced coccidiosis control or encourage GD.

Q. What about the use of chemical anticoccidials?

LN: They provide no antimicrobial effect and should definitely not be used in birds vaccinated against coccidiosis because chemicals are too effective: there’s a serious risk that they will kill the vaccine.

Q. What is the long-term effect of using vaccination without rotation over multiple flock cycles?

CB: Vaccination eliminates the carry-over effect and coccidial challenge declines over time with long-term use.
This is in contrast to the carryover of late-shedding coccidia, which puts pressure on anticoccidial medication programmes flock after flock, slowly eroding efficacy. Coccidial populations build up over time.
Vaccination stops the carry–over by inducing immunity early in the life of the flock and by preventing late oocyst shedding. The lack of heavy oocyst carry–over means that the coccidial challenge declines with time.
Early immunity in heavily challenged houses is induced by a combination of wild and vaccine strains. Prolonged use of vaccination can reduce the in-house challenge with successive flocks, producing continuous improvement in performance.

Q. Does the vaccine quit working if it is used for too long?

LN: No. The vaccine doesn’t quit working, but the challenge may become so low that you need to enhance vaccine cycling with environmental management.
Much of our initial house management for vaccinated flocks is designed to minimise the impact of carry-over wild strain Eimeria. The wild strain challenge declines with prolonged vaccine use. Over time, the management strategy designed to control the wild strain may be too effective; it may actually limit effective vaccine cycling.
The vaccine itself is very mild. Management of the environment with longer, partial house brooding or increased litter moisture may be required to ensure rapid development of complete immunity.

Q. How are low-cost alternative ingredients properly used in rations meant for vaccinated flocks?

CB: You want the starter-feed formulation to enhance microflora management. Once immunity has been established and you get to the grower and finisher feeds, you can make more extensive use of alternative cost-reducing ingredients.

LN: In vaccinated flocks, we know there’s a low-level coccidiosis challenge that induces immunity in the first three weeks. You want to avoid microflora-disrupting alternative ingredients, such as dried distillers’ grains or bakery meal, during the starter phase. Enhance microflora control as needed with in-feed antimicrobials.
After three weeks, the coccidial challenge in vaccinated flocks rapidly declines. There’s minimal coccidial insult to the intestines, which makes it safer to experiment with higher levels of alternative, cost-reducing ingredients using enzymes or the antimicrobial effect of an ionophore to maintain performance at least cost.

Q. Is assistance available to help producers adjust their management to get the best performance in flocks vaccinated against coccidiosis?

CB: Yes. A Merck Animal Health poultry representative can provide all the help you need, whether you’re converting to coccidiosis vaccination or trying to improve performance if you are already vaccinating.

Further Reading

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Find out more information on coccidiosis by clicking here.