Protozoans attack the lining of a calf's intestinal tract, weakening it through malnutrition and weight loss. The two common protozoans involved are coccidiosis and cryptosporidiosis
Coccioliosis
The acute form of coccidiosis, caused by a protozoan, is characterized by bloody diarrhea and anemia. Calves 3 weeks to 6 months old are most susceptible to infection. The disease usually strikes at weaning time when calves are moved to overcrowded, dirty and wet pens. Feeding hay fed from the ground or grain from low troughs which are easily contaminated by fecal material increases the likelihood of infection.
Once ingested, coccidia invade and destroy the epithelial cells lining the intestine. Diarrhea, sometimes bloody, and anemia are often observed in clinically affected calves. Calves that survive coccidiosis develop longlasting immunity. Pens should be maintained in dry areas with a sufficient drainage system. Overcrowding should be avoided and waterers and feeders should be constructed or located so that fecal contamination can be averted. Medicating feed and water supplies usually controls the disease without interfering with the development of immunity.
Cryptosporidiosis
These organisms are protozoans like coccidia, and are capable of infecting a variety of animals, including man. The disease is reported to be common in calves up to one month old; however, in Florida, it most frequently is observed around 7 to 10 days of age. Recent surveys on several Florida dairies have found a high incidence of cryptosporidial infection in calves between 5 and 15 days of age.
Cryptosporidia damage epithelial cells of the small intestine. This decreases the absorptive ability and surface area of the gastrointestinal tract and causes watery diarrhea. Because the infected calf cannot digest and absorb nutrients, it loses weight.
The importance of cryptosporidia as a cause of calf diarrhea is unclear; however, it has increasingly been reported as a finding in calves with diarrheal disease. Less severe experimental infections often clear up in 1 to 2 weeks, whereas naturally acquired infections are often complicated by E. coli or rotavirus and may lead to death. Like aforementioned pathogens, cryptosporidia are found in the gut of healthy calves. One study showed that neonatal calves deficient in colostral antibody are at increased risk of developing cryptosporidial-associated diarrhea. The best current treatment is good nursing care. The best prevention is to feed calves colostrum at birth. Continued feeding of colostrum through the first week of life may provide additional protection against cryptosporidia as well as other pathogens likely to infect calves during this period.
Source: B. Harris, Jr. and J. K. Shearer – University of Florida IFAS Extension