MLBA 1: February / March 2008

Coccidiosis rotation programs

By Maja Marien and Dieter Vancraeynest

     Technical Managers, Alpharma Animal Health

Coccidiosis in poultry is of great economic significance to the poultry industry since it is one of the most important complicating factors involved in gut problems. It is caused by a protozoan parasite belonging to the genus Eimeria. Chickens can be infected by 7 different species and turkeys by 7 other species that do not infect chickens. The most important species for broilers are E. tenella (blood in faeces), E. acervulina (white ladder-like lesions in first part of intestines), E. maxima (red pin-point like lesions in the midgut) and E. mitis (no typical lesions). For older chickens, two more species are important, i.e. E. necatrix and E. brunetti.

Coccidia need to invade intestinal cells in order to replicate. The next generation of coccidia can only be set free by causing the host cell to burst, so each coccidian parasite that is present in a chicken causes damage.

When only a few parasites infect a bird, the damage will not lead to clinical disease, but of course any destruction of a gut cell will lead to loss of energy and proteins, causing a higher feed conversion rate and an economic loss for the farmer.

If there is a massive infection, the destruction of gut cells will lead to severe lesions, diarrhoea and, with certain species, even death of the birds.

So it is important to note that not all the species in poultry cause mortality or severe illness, but all cause loss of performance. After replication within the gut cells, and before being released within the faeces of the chicken, these parasites transform into special survival-forms called "oocysts", which are very difficult to destroy with any disinfectant. The robustness of the oocysts is the main reason why almost every farm worldwide is infected with coccidiosis.

The big problem with coccidiosis is that it acts like an iceberg: before the top (clinical coccidiosis: lesions, disease and mortality) is noted, the base under the waterline might have ripped up the hull of the ship (subclinical coccidiosis). Subclinical coccidiosis causes loss of performance because of impaired intestinal function followed by intestinal inbalances due to leaking of plasma proteins in the gut and remnants of poorly digested feed available for bacterial overgrowth (fig 2), possibly leading to wet litter. This is the reason why poultry operations worldwide always rely on prevention by means of anticoccidial ools in order to limit as much as possible this ever present risk of damage. In a recent survey from the UK, with over 800 farmers involved, farmers indicated that coccidiosis is one of the most important predisposing factors for wet litter (Hermans, Poultry World, June 2006). This indicates that good coccidiosis control should be focused on. An important step would be to apply improved rotation programs, in order to reduce as much as possible one of the main predisposing factors.

At present a number of strategies are used for the prevention and control of coccidiosis in broilers. Management measures focusing on good sanitation, cleaning out contaminated litter, and good litter condition in broiler houses are considered of strategic value in controlling this parasitic disease. Anticoccidial prevention, however, is usually performed by administration of anticoccidial drugs, also called coccidiostats, in the feed.

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