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Predisposing factors
Coccidiosis occurs in conditions of high stocking density especially in broiler houses where there is build up of coccidial oocysts in the litter. A chicken density of more than 22 birds per m2 is a negative factor and stocking densities such as 0.7 ft2 per bird has favoured the spread of disease in commercial poultry facilities. Bad quality litter, caused by too much moisture, is another riskfactor. Cup drinkers are more often associated with coccidiosis than other systems.
The most important factor is the lighting schedule. Intermittent lighting increases the risk as compared with continuous lighting. The birds actively manipulate the litter most likely by increased mobility during the short light period, which improves conditions for sporulation and survival of the oocysts. Thus the number of infective oocysts available to the birds may be increased.
Antinutritional factors (ANF's) in the feed, mostly non starch carbohydrates such as trypsin inhibitors, lectins, tannins, which are present in the walls of various legume seeds, binds to the mucosa of the intestinal wall. This can result in damage, inactivate intestinal enzymes and interfere with protein and carbohydrate digestibility resulting in excretion of wet litter which could likely be a factor in the epidemiology of coccidiosis.
Brooder and Grower Management
When chicks are brooded in a separate area before moving them to the grower facility the brooder stays clean of infective oocysts. However chicks are at risk for coccidiosis, if they stay in the brooder longer than three weeks.
As overcrowding predisposes the birds to coccidiosis, adequate floor space and feeder/waterer space should be given to prevent overcrowding. One square foot of floor space per chick and four tube feeders per 100 chicks is recommended. The feeders should be always full of feed so as to prevent birds from pecking the litter and ingest infective oocysts.
Other several factors influence the severity of infection. Some of these include the following:
  • Number of oocysts ingested by the bird: Generally, an increase in the number of oocysts eaten is accompanied by an increase in the severity of the disease.
  • Strain of coccidia: Different strains of a species may vary in pathogenicity.
  • Environmental factors affecting the survival of the oocysts.
  • Site of development within the host: Coccidia that develop superficially are less pathogenic than those that develop deeper.
  • Nutritional status of the host: Poorly fed birds are more susceptible.
  • Age of the bird: Young birds are generally more susceptible than older ones. Old birds are generally immune as a result of prior infection. Severe damage to the caeca and small intestine accompany the development of the coccidia. Broilers and layers are more commonly infected, but broiler breeders and turkey and pheasant poults are also affected.
  • Season: Coccidiosis generally occurs more frequently during October to December of the year.
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