Chicken coccidiosis is a widely distributed protozoal disease. In production practice, it not only causes large numbers of chick deaths (the mortality rate from cecal coccidiosis exceeds 80%) but also significantly reduces poultry production performance (such as meat quality, mortality and culling rates, weight gain, and feed efficiency), resulting in major economic losses and seriously threatening the development of the poultry industry. Chicken coccidiosis poses a serious threat to chicks and pullets. Chicks aged 15 days to 30 days have a high incidence rate. Chicks that survive grow slowly and develop poorly. Damage to the intestinal mucosa causes mucosal immunosuppression, becoming a major factor in vaccine failure. Adult chickens are often carriers, and clinical signs are generally not obvious, but weight gain and egg production are affected to some extent.
Epidemiological characteristics: This disease usually occurs in seasons with frequent rainfall and temperatures of 22℃ to 30℃. It is mainly transmitted through the digestive tract. Recovered chickens and contamination of the ground and litter are the main sources of infection.
Clinical and postmortem signs: Different strains infect different sites, resulting in different clinical and postmortem signs. In clinical practice, infection with several coccidian species often occurs concurrently. The more common coccidia include the following: Eimeria acervulina. Gross lesions: Mild infections are confined to the duodenal loop. Lesions can be observed from the serosal surface as transverse white streaks, with a trapezoidal appearance. The intestine is pale and contains white fluid. In severe infections, the intestinal wall thickens, and the intestinal mucosa is covered with a dense layer of white, worm-like material.
Eimeria maxima: This species generally parasitizes the middle section of the small intestine, from the duodenal loop to the vicinity of the yolk stalk, but in severe infections it can spread throughout the small intestine. Abundant orange-yellow fluid and mucus are commonly found in the middle section of the small intestine. The small intestine is flaccid and filled with fluid.
Eimeria necatrix: Its lesion sites are similar to those of Eimeria maxima. Because it reproduces at a low rate, it is mostly found in older chickens. Infection commonly causes emphysema of the small intestine and thickening of the mucosa. The intestinal lumen is filled with fluid, blood, and tissue debris. Small white spots and red petechiae are visible in infected areas when viewed from the serosal surface. In severe infections, lesions may extend throughout the small intestine, causing intestinal distension and mucosal thickening. On the serosal surface of the small intestine in a necropsied carcass, the lesions appear as a mixture of white and black areas.
Eimeria tenella, also known as cecal coccidiosis, is the most pathogenic coccidian species in chickens. Death occurs rapidly, generally 5 days to 6 days after infection. In acute infections, death may occur within just a few hours after signs appear. The greatest effect on weight gain is seen on day 7 after infection. Weight loss due to dehydration can be rapidly recovered, but growth will lag behind. The actual cause of death is unclear, although toxicosis is suspected. Hemorrhage is clearly visible 4 days after infection; the ceca are greatly enlarged, and their lumens are filled with blood clots and fragments of cecal mucosa. By 6 days to 7 days after infection, these are ultimately excreted in the feces.
Diagnosis: Diagnosis is straightforward based on clinical and postmortem signs and laboratory testing.
Prevention and treatment: Preventive medication: Add maduramycin and other products to feed for prevention, and administer preventive medication 14 days after the peak period of the disease.
Vaccine prevention: For broiler breeders, live coccidial oocyst vaccines are currently widely used both domestically and internationally to prevent chicken coccidiosis, with ideal results. In recent years, they have also been used in commercial broilers.
Treatment: The use of anticoccidial drugs is currently the most frequently used and most effective method for preventing and treating coccidiosis. However, there are still quite a few drawbacks to their use. The most important is that drug resistance develops too quickly; therefore, anticoccidial drugs must be used appropriately.
Next, bacterial infections must be controlled.
Then, vitamins should be supplemented, especially vitamins K and B.
Because coccidiosis is ubiquitous, it has caused huge economic losses to the livestock industry. Therefore, countries are actively researching ways to prevent and control coccidiosis. To date, some measures have been taken to reduce the harm caused by coccidiosis: (1) Develop and use anticoccidial drugs in a planned and efficient manner.
(2) Strengthen husbandry management, maintain a clean rearing environment, and reduce the likelihood of coccidial infection as much as possible.
(3) Develop and use coccidiosis vaccines.
(4) A population with resistance to coccidiosis was developed through genetic engineering.