I. Causes of chicken coccidiosis
(I) Management factors. These mainly include the following: lighting, temperature, humidity, litter, stocking density, environment, and rearing methods.
1. Temperature and humidity. When the temperature in chicken houses falls below 20℃ in winter, or when conditions are very dry, the incidence of chicken coccidiosis also decreases due to poor oocyst sporulation. In spring and summer, when temperatures and humidity are high, the incidence of chicken coccidiosis is higher. It is particularly common around the plum rain season in the humid regions of southern China. During this period, because the litter is relatively damp, we often find that coccidiosis recurs.
2. Hygiene and disease prevention. Experience has shown that some large chicken farms have relatively few or no losses caused by coccidiosis because they have strengthened sanitation and disinfection and implemented disease prevention measures appropriately. By contrast, small chicken farms and individual poultry farmers are prone to outbreaks of coccidiosis because their farm conditions are poor, their technical capabilities are limited, and they do not give coccidiosis sufficient attention.
3. Experiments show that intermittent lighting carries a somewhat higher risk of coccidial infection than continuous lighting. This is because the former causes chickens to turn over the litter more actively, increasing the chance of infection while also improving the conditions for oocyst sporulation.
4. Litter management is important for controlling coccidiosis and should not be overlooked. The general requirements are that the litter be loose, dry, and shallow.
5. High-density rearing is an adverse disease-promoting factor. When stocking density is too high, air quality in the poultry house is poor, and the incidence of coccidiosis is higher. High-density flocks increase oocyst density and thus the chance of infection.
6. Different rearing systems can cause significant differences in susceptibility to coccidiosis. For chickens reared on wire floors, the chance of coccidiosis infection is extremely low. This is mainly because these chickens are less likely to come into contact with infection sources on the ground.
(II) Feed factors. Various antinutritional factors in feed, such as tannic acid, phytic acid, gossypol, and trypsin inhibitors, readily bind to the intestinal mucosa, causing damage to the intestinal wall. An imbalance in dietary electrolytes increases the moisture content of excreted feces. Both factors increase the incidence of coccidiosis. A deficiency of vitamins A and K in feed damages the digestive tract mucosa and blood-clotting mechanisms, making chickens more susceptible to coccidiosis. When feed is restricted, hungry chickens peck at the litter, increasing their chances of infection and also the disease incidence. High-quality, nutritionally complete feed can improve the body's resistance to coccidiosis. Feed components such as protein, vitamins, and minerals play an important role in controlling coccidiosis. Feeding coarse sand, pelleted feed, and high-fiber feed can also reduce the incidence of coccidiosis. In addition, antinutritional factors in feed can impair intestinal absorption, leading to increased litter moisture.
(III) Stress factors. In production settings, coccidiosis in chickens often occurs several days after a stress response. These stressors include nutritional imbalance, changes in habits, transportation, and climate changes. Severe stress responses not only promote the onset of coccidiosis but can also worsen the disease. If a flock is infected with MD, the body's immunity to coccidiosis may be disrupted, triggering the disease. Infection with IBD virus can worsen coccidiosis symptoms, cause earlier cecal bleeding, and increase mortality. The presence of aflatoxin can increase coccidiosis mortality by 40%.
(IV) Host differences. Chicken breeds, ages, and sexes differ significantly in their resistance to coccidiosis. In general, young chicks are more susceptible to coccidia; male chicks are more susceptible than female chicks; white chickens are less resistant than brown chickens; and the purer the strain, the more susceptible it is to coccidia.
(V) Drug resistance. Due to the long-term use of anticoccidial drugs, as well as improper use, coccidia can readily develop resistance to certain drugs. After any anticoccidial drug has been used for a period of time, coccidia may develop resistance or even form drug-resistant strains, and may also develop cross-resistance to other drugs in the same class or with the same mechanism of action. Therefore, selecting a suitable medication method and developing a proper medication plan can extend the useful life of anticoccidial drugs as much as possible.
(VI) Coccidia strain types, quantities, and parasitic sites. Different strains vary in pathogenicity. If the number of infecting coccidia does not reach a certain level, the individual may show no symptoms of coccidiosis. For strains of moderate virulence, when the number of infecting coccidia is too high, the number of new oocysts produced decreases correspondingly; this is called the “crowding effect.” Different strains have specific parasitic sites. If the parasitic site changes, pathogenicity may decrease or even disappear.
(VII) Relationships with other pathogens. Tissue damage and changes in intestinal function can allow various harmful bacteria to invade and multiply. Escherichia coli and coccidia interact in chickens. If a flock is infected with Marek's disease virus, its immunity to coccidiosis may be disrupted, making coccidiosis more likely to occur. Infectious bursal disease can worsen coccidiosis, while coccidiosis can greatly aggravate the harmful effects of infectious bursal disease. When coccidiosis and reovirus are present at the same time, the proportion of chickens developing hock-joint disease is much higher than when reovirus occurs alone. When coccidiosis and aflatoxin are present at the same time, mortality can reach 60%. Studies show that coccidia act synergistically with other intestinal bacteria, which can enhance the pathogenicity of coccidia. Coccidial infection can increase susceptibility to ND, MD, and IBD.
II. Prevention and control of chicken coccidiosis
(I) Maintain good poultry-house hygiene and interrupt the transmission of coccidia. Outbreaks and spread of coccidiosis are closely related to the external environment, with temperature and humidity being the foremost environmental factors. Under natural conditions in northern China, coccidiosis generally occurs during the warm, humid season from 4 to 9, and is most severe in 7 and 8. However, as most poultry farms now use intensive production systems, environmental conditions are increasingly controlled by humans, and the seasonal pattern of coccidiosis is no longer clear. In warm, humid brooders, the disease may occur at any time of year. Cool, damp conditions in poultry houses, poor hygiene, and inadequate husbandry are the main factors that trigger the spread of coccidiosis. For example, warm, humid conditions favor oocyst development, while good ventilation, dry housing, appropriate stocking density, prompt manure removal, and regular disinfection can effectively prevent the disease.
1. Maintain good poultry-house hygiene and keep the floors clean. Keep poultry houses (cages) clean and dry. Remove chicken manure promptly and compost it. Carry out routine and periodic disinfection.
2. Strictly cull diseased chicks. Obtain chicks or hatching eggs from poultry farms with reliable sources. Keep recovered chickens in separate housing from healthy flocks.
3. Ensure that feed is nutritionally complete, fresh, and hygienic. Add a range of vitamins as appropriate, especially vitamin A, to improve the chickens' resistance.
(II) Use preventive medication appropriately. During the age period when coccidiosis is most prevalent, using anticoccidial drugs to which the coccidia are susceptible is one important means of preventing the disease. The anticoccidial drugs currently in use mostly inhibit or kill coccidia during the early stages of their development. By the time bloody droppings appear, coccidia have largely completed asexual reproduction and begun the sexual stage. Medication at this point can protect chickens that have not developed obvious symptoms or have not been infected, but is unlikely to be effective in chickens with severe symptoms. Therefore, at the susceptible age (after 2 weeks) or during the epidemic season, administer preventive medication in feed or drinking water.
There are many types of anticoccidial drugs. Polyether ionophore antibiotics include monensin, salinomycin, and maduramicin; chemically synthesized anticoccidial drugs include sulfonamides, plant alkaloids, and others.
In areas with a history of coccidiosis or where coccidiosis frequently occurs, medication can be selected based on local conditions. When administering medication, pay attention to the dosage and course of treatment, and use medication for prevention and treatment scientifically and appropriately.
(III) Proper use of vaccines for prevention and control. To thoroughly address the increasingly serious problems of drug resistance and drug residues caused by drug-based control, people have gradually found a way to prevent chicken coccidiosis using vaccines. At present, the live coccidiosis vaccines used for planned immunization on chicken farms fall into four categories: precocious, intermediate, and late-maturing strains, and combined vaccines containing precocious, intermediate, and late-maturing strains. Einerivac, a coccidiosis vaccine developed by China Agricultural University, is a combined vaccine containing precocious, intermediate, and late-maturing strains; it is safe, effective, and inexpensive.
Current methods for administering live coccidiosis vaccines include oral drop, feed spraying, drinking water, and spray vaccination. The oral drop method is the best, as it can ensure 100% immunization, but it is somewhat inconvenient and causes considerable stress on large chicken farms. Spray vaccination is more suitable for well-equipped hatcheries, while drinking water and feed spraying are more suitable immunization methods for large chicken farms. Practice has shown that preventive immunization of chickens with coccidiosis vaccines is a highly promising method that will bring significant economic and ecological benefits to the poultry industry.
(IV) Herbal deworming and health supplements. The problems of drug resistance and drug residues resulting from the use of drugs and vaccines have never been fundamentally resolved. Herbal deworming and health supplements, coccidiosis vaccines, and controlling chicken coccidiosis from a nutritional perspective have brought new hope for the prevention and control of chicken coccidiosis.
Herbal deworming and health supplements: as a general rule, herbal products used for deworming and health maintenance have very few toxic side effects and leave very little residue. They can activate chickens’ ability to resist coccidiosis, strengthen disease resistance, and promote growth and development, without causing drug resistance; they are therefore a deworming and health supplement with considerable development potential.
(V) Controlling chicken coccidiosis through dietary treatment. Controlling coccidiosis by adjusting dietary nutrients and using biological enzymes is a new approach to its prevention and control, with broad prospects for development.