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Farmnote 29/96

[Reviewed March 2006]

By Marc Kabay, Veterinary Pathologist, Animal Health Laboratories, South Perth

Summary

Discusses coccidiosis in poultry, caused by Eimeria species of intestinal parasites. Covers immunity, life cycle of coccidia, symptoms and diagnosis, prevention, treatment and disinfection.

Coccidiosis in poultry is an infestation of the intestines. It affects weight gain and feed conversion and may kill birds.

Coccidiosis is common in chickens, turkeys and pheasants, less common in geese, and rare in ducks.

The coccidia (the intestinal parasites) of one poultry species do not cause disease in other species. Coccidia of sheep will not infect chickens, nor will coccidia of chickens infect sheep.

The infestation is caused by Eimeria species, which are microscopic protozoan parasites. The most important species in poultry are listed in Table 1. Most infestations under field conditions are mixed infestations, with one species of coccidia dominant.

Immunity

No immunity is passed from parent to progeny. After recovery from an outbreak of coccidiosis, birds are usually immune to further infestation by that species, but they may still be infested by other species.

Resistance to coccidiosis usually develops after 14 to 16 weeks of age.

Life cycle of coccidia

Microscopic egg-like bodies called oocysts are passed in the droppings of birds affected with caecal and intestinal coccidiosis.

With moisture, warmth and exposure to air, the oocysts develop four sporocysts. Each sporocyst contains two parasitic sporozoites. If a sporulated oocyst is ingested by a bird, the tough protective wall of the oocyst is digested and the sporozoites are released. These penetrate the lining cells of the intestines.

When a sporozoite has invaded a lining cell, it develops into a schizont containing many minute parasites called merozoites. The merozoites are released into the intestines by rupture of the schizont.

Tissue damage, including rupture of capillaries, results in loss of blood. The shock and the drastic interference with digestion causes weight loss, poor feed conversion and often the bird will die.

The life cycle is completed when male and female forms join and develop into oocysts. The oocysts pass out with the droppings. They may survive for months if protected from dissecation.

Symptoms and diagnosis

Individual sick birds that droop their wings and lack vigour are readily noted in flocks at the early stages of the disease. Droppings may be tinged with blood.

On post-mortem examination, pin-point haemo-rrhages are observed on the intestinal wall in the early stages of the disease.

A thorough examination of intestinal smears under the microscope will show oocysts or schizonts (or both).

A tentative diagnosis of the species of Eimeria involved can be made by noting the location and appearance of the small lesions.

Prevention

Two types of drugs (coccidiostats and coccidiocides) are used continuously in the feed to prevent coccidiosis.

A wide range of these drugs is available. The choice may vary depending on whether the bird is raised for meat (broilers), eggs (layers) or replacement breeding stock.

Broilers

In broilers a coccidiocide is used to prevent coccidiosis. Coccidiocides completely inhibit the development of coccidia. As a result, no immunity develops in the flock.

This total lack of immunity in a broiler flock may cause a severe outbreak of coccidiosis if drug intake has fallen and the birds have ingested large numbers of oocysts.

Coccidiocides used commonly in the broiler industry include the ionophore based drugs such as Coxistac®, made by Pfizer Agricare.

Layers and breeders

Breeders for meat or layer production and replacement layer pullets should be immune by the time they reach point of lay but should not have suffered from clinical coccidiosis during this period. To achieve this, coccidiostats are used at a low concentration in feed to prevent disease but allow some exposure to stimulate immunity. By progressively reducing the concentrations of a coccidiostat in the feed and withdrawing it when birds are 14 weeks old, sufficient immunity should have developed to safeguard the flock for the rest of its life.

The most common coccidiostats used by the layer industry are DOT (dinitro-o-toluamide) based drugs such as CCD DOT®, made by Central Chemical Distributors and DOT Premix Coccidiostat®, made by Agribusiness.

If laying birds are subsequently housed in cages, the need for immunity to coccidia is not so critical. It may be economical to feed higher concentrations of a coccidiostat until they are housed.

The risk of coccidiosis in caged birds is low if the cages allow unimpeded fall of droppings.

Several factors may cause an outbreak of coccidiosis, even if a coccidiostat is present in the ration.

• Dilution of a balanced ration by the overfeeding of grain, grass and food scraps. In this case, insufficient amounts of the drug are ingested.
• Restricted diet. When the ration arrives, greedy and bullying birds may deprive other birds of feed. Water constantly medicated with a coccidiostat may overcome this problem.
• Insufficient feeder space. Birds may not get a full quota of medicated feed.
• Poorly adjusted automatic feeders, affecting the distribution of ingredients.
• General management failures such as over-crowding, poor ventilation, leaking drinkers and wet litter.
• Lighting programs which have not been arranged to ensure adequate feed intake.
• An outbreak of another disease such as uraemia, that causes a lowered feed intake. It is not uncommon in outbreaks of uraemia to find some affected birds also have coccidiosis.
• Reduced feed intake during hot weather using a drug specifically for treating clinical coccidiosis.

Treatment

If an outbreak of coccidiosis occurs, start treatment as soon as possible. Amprolium (Amprolimix-plus®, made by MSD AgVet, and Keymix Keystat Key 25®, made by International Animal Health Products), are commonly used to treat outbreaks.

Give all drugs strictly according to the manufacturerÃ-s recommendations. Chickens on a restricted ration must be given an ad-lib diet during treatment.

Disinfection

Disinfectants containing ammonia in solution are efficient. Oocysts are highly resistant to ordinary disinfectants.

Liquid ammonia used at a 1 per cent dilution kills coccidia in 24 hours.

However, do not rely upon such disinfection as a means of prevention. Disinfectants are helpful for general hygiene, but the use of a coccidiostat is indispensable.

Table 1. Coccidia (Eimeria) species of poultry