Scours Timing Helps Indicate Cause

Written by: Skip Olson, Technical Services Veterinarian
Milk Products, LLC

If you raise calves, you know the frustrations of scours first-hand. Along with respiratory disease, scours remains one of the top two causes of illness and death in preweaned calves in the United States.1 Understanding scours episodes, and the organisms that cause them, can be helpful in diagnosing, treating and preventing the condition.

“Scours” is not a single disease, but rather a symptom of a number of different infections and digestive conditions. Scours is the calf’s response to a metabolic upset or imbalance in the digestive tract. Something as simple as a change in concentration of components of the milk diet – for example, switching from whole milk to transition milk – can trigger a case of scours.

In addition, disease-causing organisms that infect the intestine often destroy intestinal cells, resulting in the release of cellular debris, proteins, acids and minerals into the intestine. When enough intestinal damage is done, the mineral balance in the intestine is upset, and the calf responds by passing water into the intestine to re-establish equilibrium.

The resulting combination of manure, water, mucous and sometimes blood is what we see as scours. Calves can quickly become dehydrated and sometimes die due to this loss of hydration. But in addition to water, scours also causes calves to lose valuable electrolytes, which can cause acidosis (lowered blood pH) and death.

Infectious scours agents
Scours caused by infectious agents are most common and most serious. Losing calves is costly, but so are the labor and treatments (antibiotics, electrolytes, etc.) necessary to save them.

Working with your veterinarian, it is important to diagnose the cause of scours so you can properly treat the sick calves. Even more important, identifying the source can help guide the best strategy for preventing future cases.

The age of the calf when scours occurs is one helpful way of pinpointing the cause. Following are some of the most common scours-causing organisms, and the timeframe in which they usually occur:

Salmonella – While several strains of salmonella can cause calf scours, the most common is S. typhimirium, which usually affects calves between 1 and 4 weeks of age. Other infected animals and contaminated feed are the two major, on-farm sources of this bacteria. Some antibiotics have shown efficacy in treating scours caused by salmonella but you need to discuss this treatment with your veterinarian. Early delivery of high-quality colostrum provides critical protection against salmonella. Vaccination technology for both calves and dams also is available, however, strict attention to sanitation is most important.

E. coli – Calves are susceptible to E. coli at a very young age. It often is the cause of acute death as early as 24 to 36 hours, and up to a week, after birth. The diarrhea caused by E. coli often is profuse, watery and may contain blood. Severe depression and coma can also be symptoms. Providing a clean, dry calving environment and delivering high-quality colostrum – ideally, within the first hour of birth – can help defend against E. coli. It is always important to work with your veterinarian on a vaccination program.

Rotavirus – As its name suggests, rotavirus is a virus, not a bacteria. It usually affects calves from 1 to 2 weeks of age, although fecal samples may be positive up to about 4 weeks of age. Scours cases caused by rotavirus often are mild, but prevention still is important. Excellent ventilation in the calf-housing area, along with vaccinating dams, colostrum delivery, and newborn-calf vaccination, can help prevent it.

Coronavirus – This virus usually causes scours from 3 days to 3 weeks of age, although some calves may be affected up to 3 months. It is the most deadly scours-causing virus, producing rapid dehydration and acid-base imbalances. Isolating calves from older animals, and properly cleaning feeding utensils, can help prevent it.

Coccidia – Coccidial scours usually occur after calves are about 3-4 weeks of age. Infection happens earlier in life, but the incubation period is about 3 weeks. Coccidiosis often is associated with bloody scours. Several feed additives are effective in preventing coccidial infections. Keep in mind that damage to the intestine happens before coccidial scours appears, so prevention is critical.

Cryptosporidium – This parasite usually causes scours in calves around week 2 to 3 of life. Most calves eventually overcome the scours it causes after about 5 to 10 days, but it definitely interferes with early life weight gain and growth. Currently there are no drugs labeled for treating cryptosporidium; the best course of therapy is electrolytes, keeping the calf eating and patience. Cryptosporidium is spread via the fecal-oral route, so sanitary calving facilities; calf housing and feeding equipment – including drinking water receptacles – are important for prevention.

There are other infectious agents that also cause scours, and sometimes scours cases are caused by more than one organism or circumstance. For example, a digestive upset caused by diet changes or irregular intake can open the door of opportunity for an infectious organism to move in. Early delivery of high-quality colostrum is a common denominator for helping equip calves stay healthy. And, again, working with your veterinarian to diagnose the causative organism, and taking steps to prevent new infections through sanitation protocols, is the best way to bring scours under control in your herd.


Common Age for Infectious Calf Scours


1”Heifer Calf Health and Management Practices on U.S. Dairy Operations, 2007, United States Department of Agriculture, National Animal Health Monitoring System.