Diseases of Chickens
Coccidiosis occurs in many animals. It is very common in chickens and the economic cost to the poultry industry is staggering. The death rate from the disease is quite high.
Seven different species of the genus Eimeria live in the gut wall of the chicken. These single-celled, spore-forming coccidia species are host specific. Thus, turkeys are not infected by fowl coccidia. Different parts of the gut are host to different species. Only one species causes caecal coccidiosis while the others cause intestinal coccidiosis.
Faecal material from an infected bird contains oocysts, small egg-like bodies. Ingestion of this infective material results in the oocysts maturing in the host. Oocysts needs warmth and moisture to mature. Given ideal conditions, maturation takes only 24 hours. Oocysts are very resistant to most disinfectants. They are also resistant to extremes of weather. Oocysts may still be present in a poultry yard twelve months after they were deposited.
Chicks under three weeks of age are generally not affected. Until then, there is an insufficient build up of numbers to cause problems. Once affected, the birds lose condition and appear unwell. They will sit around with drooping wings and ruffled, bedraggled feathers. The head and comb may be pale in colour. The bird will develop diarrhoea with perhaps blood in the droppings. However there is often few or no symptoms but production will be affected or birds will suddenly start dying. A large number of chickens may appear sick.
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Similar symptoms appear with salmonellosis, blackhead and necrotic enteritis. Post-mortem examination of birds dying of caecal coccidiosis will reveal the caeca (blind gut) swollen and engorged with blood and cheesy plugs. With intestinal coccidiosis, findings may include any or all of – reddish spots on the intestine, swollen and blood-engorged intestine, inflammation of the lower section of the small intestine and white streaks or spots on the upper section of the intestine.
Coccidia require warmth and moisture to thrive. Keeping litter dry helps a great deal in preventing coccidiosis. Good husbandry includes not overcrowding birds and ensuring that ventilation is adequate. Cleaning boots, changing clothes between sheds, drip-free water lines and eradication of rodents will all assist in minimising the transmission of the disease.
Effective vaccines are now available. The live vaccines expose the bird to small doses of coccidiosis and an immunity is built up to the most virulent species. There is also a wide selection of drugs available to assist in preventing and treating the disease. These coccidiostats should be chosen carefully with consideration of the type of flock, type of coccidia and the outcome desired. Coccidiostats are often added to feed or to drinking water. To be of any use, the level of coccidiostat in the feed needs to be at an optimum level, the birds need to ingest a sufficient amount and the additive must not be withdrawn before the birds have developed a certain amount of immunity. Vitamins A and K have a major role to play in reducing the severity of a coccidiosis outbreak.
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Low doses of coccidiostats can slow down a major build-up of coccidia. At the same time, steps taken to minimise the build-up of oocysts will assist in preventing coccidiostats from succumbing to heavy infections.
A combination of good hygiene plus the assistance of coccidiostats is the best way of containing coccidiosis to acceptable levels.
Links to my other articles on chickens:
ISA Brown Chicken - Characteristics
Rhode Island Red Chicken - Characteristics
Raising Backyard Chickens
Plymouth Rock Chicken - Characteristics