Coccidiosis

Coccidiosis in chickens is caused by several different species of coccidia, which are single celled parasites that live in and damage different parts of the gut wall of their host resulting in nutrient malabsorption, dehydration and blood loss, and make the bird susceptible to secondary infections. Coccidia are host specific, which means that the coccidia that infect other birds do not affect chickens, and vice-versa.

The different species of coccidia cause either intestinal coccidiosis (the majority) or caecal coccidiosis (1 species). More than 1 species of coccidia can infect the same bird at the same time.

Coccidiosis is common in poultry throughout the world, including in Queensland.

Infected birds excrete the infective stage of coccidia in their droppings (small egg-like bodies called oocysts). In the right conditions (warm and moist) the oocysts will quickly replicate and grow. Oocysts are consumed by birds from contaminated litter and soil. Once swallowed, the parasites will invade the gut wall where they will continue to grow and multiply.

Coccidia can complete their life cycle in 2-5 days, so numbers can build up quite fast.

Common signs of infection include:

• droopiness and depression
• pale comb
• water, mucous and blood in the droppings (blood may be an indication of caecal coccidiosis)
• loss of appetite
• loss of condition
• ruffled feathers
• whitish soiling around the vent (more common in intestinal coccidiosis).

Definite diagnosis can only be confirmed by post-mortem examination of the gut.

Coccidiosis can reduce the performance of both meat and laying flocks. For example:

• reduced growth rates
• poor feed conversions
• reduced egg production
• poor egg shell quality.

Birds gradually become immune if they are exposed to a low level of infection, but clinical disease occurs if the coccidiosis challenge is too great. Immunity to 1 species of coccidia does not protect poultry against other coccidial species.

As coccidia infect and damage the gut, infected poultry are more likely to develop secondary gut infections.

Caecal coccidiosis

This is the most severe form of coccidiosis and can result in up to 50% mortality of the flock. Often, a large percentage of chickens are sick and birds may die suddenly before symptoms are obvious.

Intestinal coccidiosis

The onset of intestinal coccidiosis is often slower to develop, with a lower but steadier mortality rate. Outbreaks are more likely to occur in flocks between 6–20 weeks of age.

Birds of almost any age may be affected. Problems are less likely in chicks under 3 weeks of age because the parasites take time to build up in sufficient numbers to cause problems.

Prevention

Practising good farm hygiene and biosecurity, such as rodent control and cleaning boots before entering sheds and ranges, will help to reduce the spread of oocysts. Because coccidia require moisture to become infective, avoid wet litter by managing drinkers, ventilation systems and working litter as necessary.

Hygiene practices alone may not always be sufficient and other methods may be required.

Vaccination

Vaccination programs can help to reduce the incidence of coccidiosis in flocks. Effective live vaccines are now available in Australia. These ensure the birds are exposed early in life and develop immunity to the most virulent species of coccidia. Closely follow the manufacturer’s recommendations for effective vaccination.

Medication

Medication programs may be used as an alternative to vaccination. A wide selection of anti-coccidial drugs (coccidiostats) are available for prevention and treatment. The choice of drug will depend on the type of flock, the type of coccidia and the aim of the medication program.

As a preventative measure, low dose rates of coccidiostat may be used to slow down a major build-up of coccidia, reducing the challenge to the bird, and thus preventing outbreaks while allowing immunity to develop. Minimising the build-up of oocysts using other management strategies will greatly assist the efficiency of a coccidiostat program since coccidiostats can be overwhelmed by heavy infections.

Outbreaks of coccidiosis may occur if the:

• level of coccidiostat in the feed is too low
• birds are not eating enough
• coccidiostat is withdrawn too early (before immunity has developed).

Coccidiostats are available that can be added to the feed or water. Most have withholding periods and medication programs must take this into account. Many are not available for use in commercial laying hens. If used in backyard flocks, it is important that any withholding periods are adhered to and any eggs produced during this period are discarded.

Once coccidiosis has been diagnosed, treatment should start immediately. Consult a veterinarian and always check the label and any withholding periods that may apply.