22/08/2021
Calf diarrhea, or scours, is a relatively common problem on many cow/calf operations. Although most cases result in only mild diarrheas, some may cause severe dehydration, depression, and possibly death.
Causes: Scours are caused by bacteria (E. coli, Salmonella spp., Clostridium perfringens type C), viruses (coronavirus, rotavirus, and protozoa (Cryptosporidium parvum, or ‘crypto’, and in older calves – coccidia of the Eimeria spp.). Most of these infections are actually carried and perpetuated by adult carrier animals. Disease results when management and environmental conditions favor their transmission and reduced resistance in the calf. In fact many of these organisms are present on many, if not most, farms but may not cause enough loss to be recognized until conditions are favorable for an outbreak of scours. As an example, in a recent Ohio State study of Cryptosporidium parvum on dairy farms, all four farms studied were infected, and over 85% of all calves on each farm became infected during the first 3 weeks of life. Calf scours were not identified as a significant problem except on one farm on which Salmonella in scouring calves was also identified. Studies by the National Animal Health Monitoring System suggest that at least 40% of cow/calf operations have Cryptosporidia infections. Cold and wet weather, mud, overcrowding, poor sanitation, poor nutrition of the cows, and dystocia (or calving difficulty) are all factors that favor the development of scours.
Protection: Immunity to most infections is seldom absolute. Vaccines may prevent disease but not prevent infection. Vaccines are tools used to raise the resistance of an animal to an infectious agent. Presently, vaccines for some of the infectious agents that cause calf scours are available. They may be given to the cow before calving, or to the calf, depending upon the product. It is important to remember that an immune response takes time to occur. Most vaccines require two initial doses about 4-6 weeks apart and annual boosters for best results. Unfortunately, the disease agents that cause serious calf scours usually attack in the first week or two of life – too quickly for most vaccines to stimulate protection if given to the calf.
When you are vaccinate the cow to prevent calf scours, you are really trying to stimulate high levels of antibodies in the colostrum. For this to happen, it is best to give the booster vaccination, or the second dose of the two-shot initial series, about 4-6 weeks before expected calving. Colostral antibodies are moved from the blood to the udder in the last 6 weeks of gestation, so vaccines given just before this period stimulate the highest levels of protection. Calves absorb the antibodies from the colostrum, but some of this antibody can act on infectious organisms right in the gut. Adequate colostrum is crucial to survival of the calf (more on this later). Colostral antibodies only last a short time and give the calf ‘passive’ immunity. Vaccines given directly to the cow or calf stimulate ‘active’ or ‘acquired’ immunity in the vaccinated animal that may last months to years.
Specific prevention strategies: E. coli (colibacillosis or ‘white scours’) and Clostridium perfringens type C (‘bloody dysentery’) usually cause diarrhea in the first 10 days of life, and research has shown that colostrum from properly vaccinated cows will usually protect their calves from these infections. Not all farms have problems with these organisms, but they are potentially deadly. Bovine rotavirus and coronavirus are common on many beef and dairy farms. Good nutrition and sanitation prevent most infections from becoming severe, however, these viruses occasionally cause severe problems and lots of sick calves. Research at the Ohio Agricultural Research and Development Center (OARDC) at Wooster, and elsewhere, has suggested that the vaccines available for these viruses are not highly protective. Vaccines are commercially available to give to the cow (colostral protection) and to the newborn calf. Vaccine given to the cow may not stimulate sufficiently high amounts of protective antibodies in the colostrum. The live vaccine designed to be given to the newborn calf must multiply in the intestine in the presence of colostrum to work. In a recent study at the OARDC, the live vaccine virus administered to germ-free calves was only rarely recovered from their stools which suggested that the virus reproduced poorly, or not at all, in the gut. Producers and veterinarians have used these vaccines, but controlled studies demonstrating their effectiveness in the field are limited.
Vaccines labeled for ‘crypto’, coccidia, and Salmonella-caused scours in calves, are not available. Some commercial products designed to give the calf preformed, or passive, antibodies to specific infections are available. An example of this is a specific type of antibody to the K99 antigen sold for prevention of E. coli diarrhea. These products are administered at birth, are active in the gut, and only persist for a short time. They may, however, get the calf through the critical period of the first 2 weeks in herds with this problem. Some colostrum substitutes have been used as scours prevention tools, but there is little research to support their effectiveness.
Preventing calf scours with vaccine alone is likely to be disappointing. Good nutrition of the cow, proper timing of vaccines when used, and insuring that the calf gets a good supply of colostrum are things we can do for the animals. Managing the environment is often neglected. Cold, wet, drafty calving areas, especially where there is high animal concentration (as in barns), increase the risk that calves will be exposed. Remember that for many infectious diseases, just one organism is not enough to initiate clinical disease. However, once the first case develops, even a clean environment can become extremely contaminated rather quickly. Calves with E. coli scours may be shedding billions of bacteria in a single stool. A similar situation occurs with the viruses. In our work with crypto, we measured the shedding of Cryptosporidium parvum as high as 17 million oocysts per cc of stool in some calves. With this organism, infection may occur with ingestion of as few as 10 oocysts. Isolation of scouring calves and their mothers and moving healthy cow and calf pairs out of the calving area as soon as possible can help reduce the contamination and avoid exposing more susceptible calves. Clean, well-drained, sunny pastures that have plenty of space for the animals help reduce build up of disease-causing organisms. Ideally, the cows should be kept out of the calving area until calving begins.
One last consideration. Salmonella and Cryptosporidia infections can be transmitted from cattle to humans. Sometimes the disease produced in people can be severe. Be careful about wearing dirty clothes and shoes into the house and wash up before eating or preparing food. Some people still bring sick calves into the house to give them better care and warm them up. This practice can be potentially dangerous with some scours causing organisms.
Raising cattle is always challenging, and usually rewarding. Producers should work with their veterinarian to identify and monitor the causes of disease on their farm. Accurate diagnosis, a good knowledge base, and careful planning are necessary to develop cost effective strategies to reduce the incidence of diseases such as calf scours.
