– Dr. Michelle Arnold, DVM – Ruminant Extension Veterinarian (UKVDL)
What is “coccidiosis”?
Coccidiosis, also known as “cocci”, is a disease of calves due primarily to two species of protozoan parasite, Eimeria bovis and Eimeria zurnii. In the clinical or observable form of the disease, calves have diarrhea, often bloody, that can lead to death from damage to the intestinal tract, specifically in the lower small intestine, cecum, and colon. “Subclinical” infection without noticeable diarrhea can still cause gut damage resulting in depressed appetite, decreased feed efficiency, and poor weight gain. How “sick” animals get depends on which species of Eimeria is involved, the level of exposure, and any associated stressors such as weaning, transport, poor nutrition or weather extremes occurring at the time of infection. Coccidiosis can be seen in calves as early as 3 weeks of age, but it is diagnosed most frequently at stressful times such as weaning or at entry to a backgrounding operation or feedlot. Cattle generally develop immunity to disease by 1 year of age, meaning they continue to harbor and shed coccidia without the ill effects. Healthy older animals can spread the organism to younger, vulnerable stock.
How is the organism transmitted?
All bovine Eimeria have a “fecal-oral transmission cycle”, in which the infective form of the organism (the “oocyst”) is passed in the feces of infected cattle and consumed by calves in contaminated feed or water. Coccidia are “host-specific”; the Eimeria species that infect cattle do not infect any other species of animal and vice-versa. Calves infected for the first time shed the greatest number of the infective “oocysts” and quickly contaminated their environment. The life cycle of Eimeria is completed in a calf within 2-4 weeks and millions of oocysts may be produced in that time. Once the oocysts leave the calf in the feces, the oocysts “sporulate” and can survive weeks to months outside in the right conditions of moderate temperature and high moisture. Buildup is most common in areas where animals congregate or are crowded together, especially around watering and feeding facilities. However, direct exposure to sunlight and drying will kill the organism.
Figure 1: From “Coccidiosis in Large and Small Ruminants”, Veterinary Clinics of North America, Food Animal Practice (2018), 34, p.202.
What does a calf with coccidiosis look like?
After a calf swallows sporulated oocysts, the organism begins a very complex reproductive cycle, both asexual and sexual, within the cells that line the calf’s intestinal tract (see Figure 1 for a complete review of the life cycle). When the reproductive cycle is finished and the newly formed oocysts are mature, they break open the intestinal cells and are released into the gut and passed in the feces. The damage to the gut caused by this rupture of intestinal cells is what causes the disease symptoms. The most common sign Continue reading Bovine Coccidiosis-Frequently Asked Questions →
