Coccidiosis Control

Although much is now known and understood about coccidiosis in broiler chickens, outbreaks of the clinical and sub-clinical disease are not uncommon, writes Jackie Linden, editor of ThePoultrySite. A recent paper given by Dr Hector Cervantes reviews how to recognise warning signs, prevent and treat the disease to avoid major losses in the flock.
calendar icon 23 October 2008
clock icon 11 minute read


Coccidiosis is a common parasitic disease of broiler chickens caused by single-celled protozoan parasites of the genus Eimeria which are commonly referred to as coccidia, explained Dr Hector Cervantes of Phibro Animal Health Corp during a presentation at the 2008 North Carolina Broiler Supervisors Short Course.

He said that there are two types of coccidiosis:

  • clinical coccidiosis in which the affected birds show typical symptoms of the disease, such as bloody droppings and increased mortality, and
  • subclinical coccidiosis because the affected birds do not show visible symptoms of the disease but when a random sample of birds is examined, the presence of the gross lesions and the coccidia are found.

Because most broiler feeds contain anticoccidial drugs, cases of clinical coccidiosis are rare. However, the most frequently diagnosed subclinical disease of broiler chickens in the USA1,2. It is difficult to diagnose and treat because the birds appear normal although their performance is usually substandard.

As long as broiler chickens are continued to be raised in confinement under the current production systems, says Dr Cervantes, the prevalence of subclinical coccidiosis is unlikely to change, yet no new anticoccidial drugs are being developed. Prevention and control methods must be used to minimize the negative impact of subclinical coccidiosis on broiler flock performance.

Important Coccidia in Broiler Chickens

After describing the lifecycle of Eimeria, Dr Cervantes turned his attention to the types of coccidia. Although there are seven widely recognized species of coccidia, only three of them cause most of the problems related to coccidiosis in the USA: Eimeria acervulina, E. maxima, and E. tenella.

Each species of coccidia has its own unique area of the intestinal tract. For example, E. acervulina lesions are found in the upper small intestine, while those of E. maxima will be found in the middle small intestine and E. tenella lesions in the caeca. It is important to identify the type of coccidia affecting the flock as they require different treatments.

Diagnosis of Coccidiosis

Despite most broiler flocks are raised with anticoccidial drugs added to their feed, drug resistance - especially to chemical anticoccidials or feed mixing errors - may lead to clinical coccidiosis.

Birds with clinical cases of coccidiosis frequently display a typical 'sick bird' attitude with depression, prostration, huddling under the heat source as if chilled, soiled vents and watery or bloody droppings. One of the first signs of clinical and even subclinical coccidiosis may be paleness.

In birds that have recently died, post mortem examination should start with examination of the intestinal tract and the caeca for the presence of gross lesions. Gross lesions caused by E. acervulina are usually the most prevalent and are usually confined to the upper small intestine (duodenum), although some times they may extend to the mid-gut (jejunum). The lesions have a unique appearance, consisting of white patches or transverse white lines inside the gut that may already be observed from the outside.

Lesions of E. maxima comprise multiple petechial (pin-point size) haemorrhages often seen from the outside of the mid-gut area, in addition, segmental ballooning or enlargement of the mid-gut with presence of orange-tainted mucous may be noted. However, unless the lesions are typical they are harder to identify than those caused by E. acervulina and E. tenella and therefore it is highly desirable to confirm its presence by identifying the presence of coccidial oocysts (eggs) in a scraping from the mid gut under a microscope.

Gross lesions of E. tenella are confined to the caeca and consist of the presence of haemorrhages on the outside or inside of the wall of the caeca, free-blood or a chocolate-coloured fluid content inside the caeca with a thickening of its wall or the presence of a large core of cellular debris and blood. E. tenella can kill birds so dead birds in a flock with increased mortality should always be examined for the presence of lesions compatible with E. tenella infection or caecal coccidiosis.

Coccidiosis Prevention

Coccidial oocysts are extremely resistant to environmental conditions and disinfectant agents so eradication of coccidiosis from chicken houses by litter removal, cleaning and disinfection is not feasible.

Since the early 1950s, writes Dr Cervantes, there have been two main tools to prevent and control coccidiosis in broiler flocks. Anticoccidial agents added to the feed have been used since the mid-1950s and have been instrumental in allowing the expansion of the broiler industry to what it is today.

For many years coccidiosis prevention and control relied on the use of synthetic anticoccidials, commonly referred to as chemicals. In many cases, resistance to these drugs quickly occurred - within 1 to 3 years - and they became ineffective. Of this group, only nicarbazin remains effective today.

A major breakthrough in the prevention of coccidiosis through feed medication occurred in 1972, with the launch of the first polyether ionophore anticoccidial, monensin. This type of anticoccidial agents have been commonly referred to as ionophores, a term derived from their general chemical structure. They are the most widely used drugs for coccidiosis prevention in broilers. Each has a different mode of action and so no significant resistance has developed. Monensin, for example, is still used successfully more than 35 years after its introduction.

The second method for the prevention and control of coccidiosis in broiler chickens that has been available since 1952 in the USA, is through the use of live non-attenuated coccidiosis vaccines. For many years, the use of live coccidiosis vaccines was restricted to broiler breeder replacements.

The introduction of better and more practical vaccination techniques, e.g. the administration by coarse-spray or gel-spray cabinet at the hatchery, has resulted in more uniform administration and better protective immunity. Use of coccidiosis vaccines has increased in broiler chickens but this remains a relatively minor use compared to anticoccidials drugs in the feed.

New methods of administration of live coccidiosis vaccines, like the in-ovo injection method into embryonated chicken eggs at 18 days of incubation, allowing precise individual dosing and the early development of immunity.

Anticoccidials and Vaccines

Dr Cervantes set out the products available in the US in three tables: chemicals and chemical-ionophore combinations (Table 1); ionophores (Table 2) and vaccines (Table 3).

Table 1. Chemical and Chemical+Ionophore Anticoccidials for Broilers in the USA
Trade Name Chemical Manufacturer
Nicarb Nicarbazin Phibro
Amprol Amprolium Merial
Robenz Robenidine Alpharma
Zoamix Zoalene Alpharma
Coyden Clopidol Huvepharma
Clinacox Diclazuril Schering-Plough
Maxiban Nicarbazin+Narasin Elanco

Table 2. Ionophore Anticoccidials Available for Use in Broilers in the USA
Trade Name Ionophore Manufacturer
Aviax II Semduramicin Phibro
Bio-Cox Salinomycin Alpharma
Sacox Salinomycin Huvepharma
Coban Monensin Elanco
Monteban Narasin Elanco
Avatec Lasalocid Alpharma

Table 3. Live, Non-Attenuated Vaccines for Use in Chickens in the USA
Trade Name Target Bird Manufacturer
Coccivac-B Broilers & roasters Schering-Plough
Coccivac-D Layers & breeders Schering-Plough
Immucox Chickens I Broilers & roasters Vetech Labs
Immucox Chickens II Layers & breeders Vetech Labs
Advent Broiler chickens Viridus (Novus)
Inovocox Broiler chickens Embrex (Pfizer)

These drugs are commonly added to the starter and grower feeds but not to the finisher or withdrawal feeds.

When the same ionophore anticoccidial is added to the starter and grower feeds, this is popularly referred to as a straight program. These are commonly used in spring and summer. In some straight programs, the concentration of the anticoccidial may be increased in the grower feed to provide maximum protection at the time of peak coccidial oocyst shedding (3-4 weeks). This is known as a step-up program, in other cases, the concentration of the anticoccidial may be decreased in the grower or finisher feed, this known as a step-down program.

In other cases, a chemical anticoccidial is added to the starter feed and an ionophore anticoccidial to the grower feed(s), this is popularly referred to as a shuttle program. These minimise anticoccidial resistance becasue the time of exposure to the same drug is limited. However, other important factors must be considered: for example, when the starter feed is given for just 14-18 days, the typically strongest chemical anticoccidial will not be consumed during the time of peak coccidial oocyst shedding.

When live vaccines are used, their use is primarily limited to the summer. Dr Cervantes emphasised that because the current vaccines contain live non-attenuated coccidia and because they induce immunity in the bird by cycling through it, the vaccines induce some lesions. These lesions stimulate active immunity but they also predispose the bird to necrotic enteritis, a fatal disease caused by Clostridium perfringens.

Therefore, Dr Cervantes recommends using an antibiotic growth promoter in the feed with solid anti-clostridial activity (such as virginiamycin) when live coccidiosis vaccines are used.

Another important factor to consider when live coccidiosis vaccines are used is the amount of moisture of the litter. Very dry litter is undesirable because in slows the development of protective immunity against coccidiosis in vaccinated birds.

Finally, other important factors to consider include the timing of the release of the birds from partial house-brooding to whole-house brooding for proper 'seeding' of the house with the vaccine oocysts, and the quality and nutrient content of the feed.

Coccidiosis Treatment

In spite of our best efforts, cases of clinical coccidiosis may occur from time to time, according to Dr Cervantes.

This could be due to a variety of reasons. These include:

  • the feed mill inadvertently omitting the the anticoccidal drug or including too low a dose
  • the birds may have been offered the withdrawal feed for too long a period of the feed, or
  • the coccidia involved might have suddenly developed resistance against the drug.

Keep in mind that outbreaks of coccidiosis may also occur due to more indirect causes, warned Dr Cervantes, for example, birds that are immuno-compromised or with a deficient immune system (regardless of the cause) are more likely to suffer from outbreaks of coccidiosis. Also, if there is wet litter in the house, the high number of infective eggs may overwhelm the best preventive drug. Management practices that restrict access to light, water or feed - whether intentional or accidental - or increase stocking densities can also increase the problem.

Prompt resolution of the problem can prevent significant losses to the producer.

Key points to remember regarding treatment are:

  • Pick for treatment the drug most likely to be effective for the type of coccidiosis that you want to control
  • Ensure the water lines have been flushed and do not contain residues of other drugs or water-administered supplements (vitamins, electrolytes, etc.)
  • Sulphonamides are more stable and effective at neutral to alkaline water pH
  • Remember that the required withdrawal periods varies between sulphonamides, and
  • Be mindful of label directions and withdrawal periods to ensure efficacy and avoid tissue residues.

Table 4 lists the drugs available for the treatment of coccidiosis in broilers, the manufacturer's recommended dosages, duration of therapy and type of coccidiosis most likely to respond favourably.

Table 4. Guidelines for Treatment of Coccidosis in Broiler Chickens1
Trade Name Active Ingredient Dosage & Treatment Duration2 Type of Coccidiosis Most Likely to Respond Favourably
Amprol 9.6% oral solution Amprolium 41 fl oz/gallon stock solution for 3-5 days; then 10.25 fl oz/gallon stock solution for 7 days Severe outbreaks of caecal coccidiosis
Amprol 9.6% oral solution Amprolium 20.5 fl oz/gallon stock solution for 3-5 days; then 10.25 fl oz/gallon stock solution for 7 days Moderate outbreaks of caecal coccidiosis
Amprol 128 - 20% soluble powder Amprolium 20 oz/gallon stock solution for 3-5 days; then 5 oz/gallon stock solution for 7 days Severe outbreaks of caecal coccidiosis
Amprol 128 - 20% soluble powder Amprolium 10 oz/gallon stock solution for 3-5 days; then 5 oz/gallon stock solution for 7 days Moderate outbreaks of caecal coccidiosis
Albon - 12.5% drinking water solution & soluble powder Sulphadimethoxine 0.05% in the drinking water for 6 consecutive days Outbreaks of intestinal coccidiosis
Various Sulphaquinoxaline 0.04% in the drinking water for 2 days; off 3 days; 0.025% in the water for 2 days; off 3 days; 0.025% in the water for 2 days Severe outbreaks of intestinal coccidiosis
Various Sulphaquinoxaline 0.025% in the drinking water for 2 days; off 3 days; on 2 days; off 3 days; on 2 days Moderate outbreaks of intestinal coccidiosis
Poultry Sulfa Sulphamethazine; Sulphamerazine; Sulphaquinoxaline 0.04% solution for 2 days; plain water for 3 days; 0.4% solution for 2 days Coccidosis caused by E. necatrix or E. tenella
1 Always read and strictly adhere to manufacturer's label directions for use and withdrawal periods
2 Dosages per gallon of stock solution based on medicator set to dispense 1 fl oz/gallon of drinking water.


1. Cervantes, H., 2002. Incidence of pathological conditions in clinically normal broilers from different regions of the USA. 51st Western Poultry Disease Conference, May 1-4, Casa Magna Marriott Resort, Puerto Vallarta, Jalisco, Mexico, 220-223.
2. Cervantes, H., 2006. Incidence of subclinical diseases and pathological conditions in clinically normal broilers from 3 production complexes sorted by sex and age. 143rd Annual Convention of the American Veterinary Medical Association and 50th Annual Meeting of the American Association of Avian Pathologists, July 15-19, Hawaii Convention Center, Honolulu, Hawaii.
3. Johnson, J. and W.M. Reid, 1970. Anticoccidial drugs: Lesion scoring techniques in battery and floor-pen experiments with chickens. Exp. Parasitol. 28: 30-36.

Hector Cervantes, DVM, MS, Dip. ACPV is Manager of Poultry Technical Services for the North American Region for Phibro Animal Health Corp., based in Watkinsville, Georgia, USA.

Further Reading

- You can view Dr Cervantes' full paper by clicking here.

October 2008
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