Coccidiosis in Chickens


I realize this article is long but it is well worth taking the time to read.  It could help save a chicks life.




If you have chickens chances are you have already had to deal with Coccidiosis.  If you ask 10 different poultry keepers how to deal with coccidia you are likely to get 10 different answers, but all will agree on one thing for sure, it can be deadly to chicks.

Poultry coccidiosis is one of the most economically devastating diseases affecting the intensive poultry industry worldwide (Williams, 1999, Shirley et al., 2004 and Morris et al., 2007)  Coccidia are distributed worldwide in poultry, game birds reared in captivity, and wild birds.

Species of Coccidiosis in Chickens

Coccidiosis in poultry is caused by Eimeria species of which are microscopic protozoan parasites.  Coccidiosis is species specific, in that other animals can get coccidiosis (dogs, cats, horses, pigs, cows etc) but they can not get it from chickens, and it can not be passed between other species, ie dog to cat, chicken to cow and so on.

Chickens are susceptible to at least 11 species of coccidia, two of which cause the most damage, Eimeria tenella  causes the cecal or bloody type of coccidiosis,  and E. necatrix, which causes bloody intestinal coccidiosis (both are susceptible to sulmet)

Eimeria tenelia
This parasite develops in the cells of the ceca, which are the two blind sacs near the end of the intestine. It is one of the most pathogenic (disease producing) coccidia to infect chickens. This acute infection occurs most commonly in young chicks. Infections may be characterized by the presence of blood in the droppings and by high morbidity and mortality.

E. necatrix
E. necatrix develops in the small intestine (early stages) and later in the cecum (sexual stages). Like E. tenella, it develops within deeper tissues of the small intestine and is a major pathogen of poultry.

The most common nine Eimeria species recognized are E. brunetti, E. maxima, E. necatrix, and E. tenella were highly pathogenic, E. acervulina, E. mitis, and E. mivati were rather less pathogenic, and E. praecox and E. hagani were regarded as the least pathogenic.


How Coccidiosis is transmitted

Facts to know:

Coccidia are present in almost every poultry-raising operation.  Coccidia is in the intestinal tract of all chickens.   Coccidia oocysts can be carried on shoes, poultry dishes, clothing,  wild birds and insects.  Cockroaches and flies can mechanically carry coccidia from one place to another.  Oosysts have been found in dust inside and outside the poultry barn.   It would be nearly impossible to prevent coccidiosis.  There is no “age of immunity”.  Chickens do not build immunity from age.  The hope is to help the chickens to build an immunity and remain healthy in the process.


Coccidia oocycst are passed in the feces.  Fresh oocysts are not infective.   However, under appropriate conditions, heat (temperatures 70-90 F), humidity, moisture and oxygen,  oocysts sporulates to become a mature infective oocyst.  They are then eaten by the chicks/chickens and infect the intestinal tract.  The degree of infestation depends on the amount and type of infective oocysts ingested.

Chicks can build up immunities to coccidiosis, however they must build an immunity to each of the varieties individually, they do not get cross protection because they were infected with one particular form.   What that means is that you may have 5 of the 9 most common forms of coccidia on one section of your farm.  Your chickens build immunities to those species.  Then  you move your birds to another section of the farm that may have 4 additional species of coccidia and you have an outbreak of coccidia of young point of lay pullets that were moved.  Always use caution when moving birds from one place to another on your own farm and bringing in birds that may not be immune to the coccidia on your farm.  Remember, the only way the birds can get immunities is to be exposed to the disease.

This contributes to the phenomenon of getting healthy roley-poley (not sure that is a word) chicks and in two-three weeks you begin to lose them to coccidia.  Immediately most people believe the chicks must have had it when they arrived.  That may be in some instances, but probably more likely they had built up good immunities to the coccidia species they had been exposed to in their own environment, but need to do so for additional species in their new home.  This is the time when most peoples will say “no, I cleaned my brooder”.  Well unless you are putting them in a brand new brooder or an area of your farm where birds have never been, it is probably not likely their pen is completely free of oocysts, especially if you are putting them in with “healthy” chicks that  you already have.  Not all disinfectants are created equal.  Very few are affective against coccidia, but I will discuss that a little further down.

This brings up another point, an issue with raising chicks on wire.  While this seems like a good idea, it does keep them clean and unexposed to feces contaminated with oocysts, but that in it’s self presents the problem.  The chicks raised on wire will have no  immunities to coccidiosis.   Then, when they are juveniles they are put outside on the ground or with other chicks in a grow-out pen where they are fully exposed to coccidia with virtually no resistance.   A few weeks after they are put outside they appear sick and begin to die.  Again the only way they can become immune to coccidia is to be exposed to it.  I will discuss the ways to accomplish that a little further down the page.

I also want to add that sometimes you can do everything possible to ward off a heavy infestation and chicks still begin to die.  It can happen in the best situation.  The most that we can do is make conditions difficult for coccidia to thrive and watch for early signs during the period of new immunity.  Vaccinating or coccidiostats are a good idea although some people prefer to allow the chicks to get natural immunities as they would if they were raised by the momma hen.

Have an emergency medication on hand in case of an outbreak, early treatment is a must.  Over crowding, the stress of moving to a new location (inside to outside or even one brooder to another), and the stress of combining chicks that were not formerly together seems to be the  biggest culprits of bringing on a bout of coccidia.   Clean water and food dishes and clean litter goes without saying.  Cleanliness is always important but is not always enough.


Signs of coccidiosis can range from none to bloody diarrhea, weight loss,ruffled feathers, huddling, general depression and anorexia.  Infected birds sometimes peck at the food dish simulating eating or going from food dish to food dish but not actually eating from any of them.  Mortality can range from mild to severe, depending on the species of coccidia and the saturation.  Chicks are most sensitive between the age of 3 – 5 weeks.

By the time clinical signs are observed, especially bloody diarrhea,  it is sometimes too late to treat successfully (by all means still treat).   One reason  treatment doesn’t work at this stage is because it usually entails 5-7 days of medication, and sometimes the chicks are just too weak to actually eat or drink the medication.  Occasionally the first signs you will see are chicks that seemed to be healthy yesterday begin to die today.  You could lose an entire brooder of chicks in one day before you realize they are infected with coccidiosis.

Chicks that do survive a heavy infestation do not flourish very well due to severe intestinal damage and inability to absorb nutrients through the gut.



In this situation I believe an ounce of prevention is worth a pound of cure.  We vaccinate all our chicks with Coccivac-D2.  We started vaccinating with Coccivac-B, then Coccivac-D was released.  After a few years of using Coccivac-D it went on a company back order while they came out with Coccivac-D2.   So for a while we were unable to get the new vaccine and did not vaccinate.  We are now able to get the vaccine and as long as we can get it we will continue to vaccinate for it.  Information about Coccivac-D2 is below.

***I need to make a correction here*** we no longer vaccinate for Coccidia.  We will still vaccinate upon request.  We have done it both ways and have decided allowing the chicks to build natural immunities to coccidia is the best for our chicks.  We do still use Toltrazuril (baycox).

It can be administered in a couple different ways.  It can be misted on the chicks, sprayed on their food or put in their water.  The vaccine is excellent but will have some failure.  There isn’t any way to know for sure that all chicks ingested the amount needed for good results, then the environment in the brooder must be right for the oocysts to sporulate and be reingested .  Also, it is a live vaccine and chicks may show signs 10-14 days after vaccination.  While most signs are minimal some could be severe.  It is advised, however, not to treat unless you believe you will lose the chick.  It is part of the process of building immunities.

Coccivac-D2 coccidiosis vaccine contains live oocysts of:

  • Eimeria acervulina
  • Eimeria mivati
  • Eimeria maxima
  • Eimeria tenella
  • Eimeria necatrix
  • Eimeria praecox
  • Eimeria brunetti
  • Eimeria hagan


  It is important to remember that no anti-coccidial is effective against all the different strains of coccidia and that over time, coccidia can become drug resistant.

There are  coccidiocides used primarily in broiler operations. Coccidiocides completely inhibit the development of coccidia. As a result, no immunity develops in the flock which could prove devastating if coccidia was accidentally introduced.

Coccidiostats are used at a low concentration in feed to prevent disease but allow some exposure to stimulate immunity.


BayCox (Toltrazuril):  (BayCox is not available in the USA)

During the period that I was unable to get the Coccivac-D2, I used Toltrazuril generic for BayCox (I do not recommend the generic form).   Toltrazuril controls all intracellular stages of the pathogen’s life cycle in the intestine, without impairing the chicken’s ability to acquire natural immunity against coccidia.  It is administered in the water for 2 days consecutively at about 4-5 days old.  That is the new recommended usage. 

When I first started using it a few years ago the recommended dosage was to begin at 2 weeks of age for 2 consecutive days, then weekly for 2 consecutive days till the chicks were about 5-6 weeks old at which time they should have a good immunity to coccidiosis.   I am not sure why the dosage has changed to just administering once.  Another good thing about this product is that it will not interfere with any other medication you may be giving, including any other coccidiostats or antibiotics the chicks might be on.  I recommend having this product on hand even if  you vaccinate or feed medicated feed  just in case of any breakthrough infections.

This is where BayCox can be purchased –I am not affiliated with these websites nor do I make any $ on sales.  (At the bottom of this page, in the comments section, it is broken down into dosages for chicks)

Sulmet is another product that I have used.  It is administered at a rate of 2 tablespoons per gallon of water for 5-7 days.  Use caution with a sulfa drug and adhere to the dosage rate exactly as overdosing can lead to crystals in the kidneys – more is not better.

Because I have only used the above treatments in the past I am not familiar with other coccidiostats but thought I would include the list below.

Coccidiostats that can be used in conventional poultry production include the following:

  • Amprolium (e.g., Amprol, Corid)
  • Bambermycin (e.g., Flavomycin, GAINPRO)
  • Decoquinate (e.g., Deccox)
  • Diclazuril (e.g., Clinacox)
  • Halofuginone hydrobromide (e.g., Stenorol)
  • Lasalocid (e.g., Avatec)
  • Monensin (e.g., Coban)
  • Narasin (e.g., Monteban)
  • Nicarbazin (e.g., Nicarb 25%)
  • Salinomycin (e.g., Bio-Cox, Sacox)
  • Semduramicin (e.g., Aviax)
  • Sulfadimethoxine and ormetoprim 5:3 (e.g., Rofenaid)
  • Sulmet



Getting into disinfectants on this page is much to long and too much information to post here.  So I will touch on disinfectants briefly and will write a complete page on correct disinfecting.  Disinfecting is just that, it is not the cleaning process.  Cleaning should always take place first with a good detergent, then disinfecting should be done.

First the only disinfectants that I am aware of that will kill oocysts is ammonium hydroxide (ammonia 10%) and Formaldehyde (Formalin).  Either should be used with caution and never together.

Strong solutions of ammonia emit intense and pungent fumes.   A mask should be used and ventilation is a must.   Ammonia is not considered effective against most bacteria and SHOULD NEVER be mixed with other disinfectants.  Ammonia and Chlorine mixed together will produce a deadly toxic gas.  Ammonia and Chlorine should not even be poured down the same drain within a short time of each other.

Formaldehyde (Formalin) in liquid form is bactericidal, tuberculocidal, fungicidal, virucidal and sporicidal. However, its carcinogenic properties limit its use. The aqueous solution (Formalin) contains 37-40% w/v formaldehyde. Formaldehyde is classified as a high level disinfectant and is chiefly used to preserve anatomical specimens.  (DC&R contains formalin)

Other common disinfectants :

Chlorhexidine                                      (No)
Chlorines – sodium hypochlorites, Clorox, Javex  (No)
Iodophores – iodine, Accept-All, Interdyne, Premise  (Limited)
Phenols – Tek-Trol, Environ, Lysol                               (Limited)
Aldahydes – Gluteraldehyde, Formaldehyde, Formalin, Aldicide  (Yes)
Quaternary Ammonia – Germkill, Proquat, Quats-D Plus, ASCEND (No)
Ammonium hydroxide (ammonia 10%)  (Yes)

Again there is just too much information on the correct  disinfecting process and products to list here.  I will dedicate a complete page to that, but I thought this information was important to supply with the coccidia information.


3 thoughts on “Coccidiosis in Chickens

  1. very good info i use amprolium20% but have never been able to bring a chick back from it.Idont now what strand mine had but they ruffel up pick at feed but cant eat its like they starve to death.

  2. I use the toltrazuril for coccidia in puppies, but I have not tried on chicks. What is the recommended dosage?

    • The dosage for chickens is 7mg/kg (or 2.2 pounds) for treatment, for control 6mg/kg. The toltrazuril 5% from is 50mg/ml, BayCox for piglets is also 50mg/ml where BayCox for poultry is 25mg/ml. So if you are using toltrazuril 5% (from or BayCox for piglets 5% the dosage would be 0.15 ml per 2.2 pounds. If you are using BayCox for chickens which is 2.5% the dosage would be 0.3ml per 2.2 pounds. Recommended dosing for control and to help build immunities is administer on day 9 and 10, 16 and 17, and 23 and 24. For treatment use as needed for 2 consecutive days. Can also be given by mouth in emergencies or extreme cases, improvement is usually seen within 24 hours.

      So what does all this mean when dosing chicks? Here is an example, keep in mind we raise Orpingtons :)

      Day old chicks generally weigh about 1 to 1.5 ounces but you won’t begin treatment till they are at least 9 days old for preventative measures/control. At a week and a half (9-10 days old) the chicks weigh about 2.5-2.75 ounces.
      So lets say you have 15 baby chicks that are 9 days old and you want to begin treatment. That would be 2.2 pounds or 1kg (yes I figured it that way :). So for 15 nine day old Orpington chicks for the 5% Toltrazuril dosing it would be approximately 0.2cc mixed in their quart waterer, mix fresh on day 2.

      Repeat on days listed above but remember to increase the Toltrazuril in their water every week as they grow. (Using BayCox for poultry at 2.5% divide the dosage above in half). Decrease or increase depending on the number of chicks you are treating.

      For easy dosing (I use baycox 5%), I use a 1 ml(cc) eye dropper and start out dosing 1/4 ml (or 1/4 eye dropper) in there quart waterer and increase weekly as needed for their weight over the next few weeks.
      Approximate weights of healthy Orpington chicks in ounces:
      DAY OLDS – 1.5
      9 DAYS OLD – 2.5-3
      3 WEEKS – 6-6.5
      4 WEEKS – 7-8
      6-7 WEEKS – 12-13

      If you are dosing by mouth, in advanced coccidia cases, one tiny drop is fine then provide the water mixture. Results are generally seen in 24 hours.

      Toltrazuril is pretty safe and overdosing is rare. It does not interfere with any other medication that the chicks might be on. I have used both tolrazuril 5% from horseprerace, and BayCox 5%, and the BayCox has better results in my opinion. However, it is twice as expensive, but again in my opinion it is worth it. It can be purchased here

      Now the disclaimer: I am not prescribing or recommending this to treat for any condition, merely giving dosages. It is always recommended to see your veterinarian to make a positive diagnosis before starting any treatment.

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