On-Farm Management of Coccidiosis Vaccines

pH Matters by Jones Hamilton


by Andrea S. Zedek, DVM, MAM, DACPV, Zedek Poultry Consulting, LLC

It is summer; that time of year when days get longer, families head to the beach or pool, and life seems to slow down a little.  It is also the time of year when many poultry companies are using coccidiosis (cocci) vaccines in their broilers.  Although some poultry companies use cocci vaccines year-round with success, the warmer months of the year are generally a good time to use cocci vaccines, due to the ability to easily ventilate poultry houses to control the environmental conditions.  Let’s take a look at coccidiosis vaccines in a little more detail.

What is coccidiosis?

Coccidiosis is a disease caused by a protozoan from the genus Eimeria.  Chickens become infected by consuming oocysts—the microscopic, hardy, “egg” of the coccidia—which are always present in the environment.  Once an oocyst is swallowed by a bird, it infects the intestine and begins reproduction, known as “cycling.”  After several developmental stages, a new generation of oocysts is shed in the feces of the bird into the litter, where the oocysts are consumed once again to continue the cycle.  After several of these cycles, a bird will usually become immune to coccidiosis.  However, allowing the birds to become naturally infected would result in large performance losses, so poultry companies employ strategies to prevent or control the coccidiosis infection.  The effects of coccidiosis infection on chickens include poor feed conversion, poor weight gain, loss of uniformity and increased susceptibility to other diseases, such as necrotic enteritis.

Figure 1. Droopy bird with ruffled feathers, clinical signs of coccidiosis

Figure 2. Bloody droppings are a clinical sign of cocci

Types of coccidiostats

Coccidiostats are substances that retard the growth and reproduction of coccidia parasites.  In modern poultry production, the typical coccidiostats in use are ionophores, chemicals, and vaccines.  Ionophores, (examples: salinomycin, monensin and lasalocid) are a type of antibiotic that allow some cycling of coccidia to take place to produce immunity while ameliorating the effects of the infection.  However, over time, resistant strains of coccidia have emerged which have limited the effectiveness of these drugs.  Chemicals, (examples: diclazuril, nicarbazin and clopidol) are very effective in shutting down the cycling of the coccidia, which results in excellent performance.

Resistance to these compounds often occurs rapidly and they become ineffective.  With a coccidiosis vaccine, the objective is to give the birds a small, controlled dose of oocysts to allow immunity to develop.  While a mild coccidial infection does occur, the chickens should be able to compensate for this by gaining weight in the latter part of the grow-out.  An additional benefit of using cocci vaccines is that they contain oocysts that are susceptible to ionophores and chemicals, so when a company transitions back to these products, higher performance is usually achieved.

In recent years, consumer demands have dictated which coccidiostats companies are able to use for some product lines, such as organic (no chemicals or ionophores) or “no antibiotics ever” (no ionophores), leading many companies to utilize coccidiosis vaccines in some, or all, of their annual coccidiostat programs.  Growers need to be aware that proper management of the house environment is critical when using a cocci vaccine, to help ensure the success of the flock.

On-Farm Management Practices

Keeping Best Management Practices (BMPs) in mind is important with any coccidiosis control program, but even more so when using a coccidiosis vaccine.  This is because the birds will need to be exposed to several cocci cycles before full immunity can be achieved, as described above.  The initial vaccination of the birds will take place at the hatchery; however, the birds will need to ingest oocysts from the litter as their “booster” shot.  In order for an oocyst to infect a chicken, it must be “sporulated,” (see figure 3) and in order to sporulate, the oocyst must have moisture.  A minimum of 20-25% litter moisture content is required to ensure sporulation can occur.  However, too much moisture can lead to excessive sporulation and an overwhelming challenge for the birds, which could result in clinical coccidiosis and poor performance.  Therefore, it is necessary to make sure there are no wet spots in the house, such as from a leaking drinker line.  In addition, the relative humidity should be kept between 50-70%, to prevent caking and house sweating, but also to ensure that the house is not too dry, which would inhibit sporulation.

Figure 3. Sporulated oocyst

While the birds are going through cocci cycling, it is important to keep stress to a minimum.  Growers should always ensure birds have proper feed, water, lighting, temperature and ventilation as soon as chicks are placed.  This will not only help to maximize productivity, it will also reduce litter eating, which could expose birds to more oocysts than ideal.   Another important consideration to minimize excessive oocyst exposure is to turn out birds from half-house brooding at the proper time.  Always follow the vaccine manufacturer’s recommendation on when to turn out the flock (usually between 7-12 days of age) and ensure the flock is evenly distributed throughout the house to allow for even seeding of the oocysts into the litter.

It is normal to see some coccidiosis lesions during on-farm necropsies while using coccidiosis vaccines.  However, it is not normal to have clinical signs of coccidiosis in the flock (see figures 2 & 3).  If the grower sees birds with diarrhea, bloody droppings, droopiness, ruffled feathers or the flock experiences an unexplained increase in mortality, it is best to call the flock supervisor or veterinarian immediately to investigate.


While there are pros and cons to any coccidiostat, the reality of the current situation is that rotation of all types of coccidiostats is necessary to preserve the effectiveness of the few coccidiostats that the poultry industry still has available.  Coccidiosis vaccines have the benefit of repopulating the poultry house litter with oocysts susceptible to coccidiostats, as well as complying with “no antibiotics ever” and organic production requirements.  With each successive cocci vaccine cycle, the coccidiosis challenge in a house decreases.  Coccidiosis vaccines, therefore, are a powerful tool in the poultry industry’s quest for sustainable coccidiosis control.

About the author

Dr. Andrea Zedek began her career majoring in poultry science at North Carolina State University and also received her veterinary degree from NCSU.  After completing a Masters of Avian Medicine (MAM) at the University of Georgia, she spent 9 years working as a technical service veterinarian for a large pharmaceutical company.  In 2014 she started her own consulting business, where she is involved in a variety of activities including production medicine, technical support, poultry welfare audits and technical writing.  Dr. Zedek is very active in the American Association of Avian Pathologists (AAAP), is a diplomate of the American College of Poultry Veterinarians (ACPV) and a Professional Animal Auditor Certification Organization (PAACO) certified poultry auditor.