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Calf Scours


Calf Scours: Infectious Causes

Sophia Morse (Veterinary Intern)


Scours, or diarrhoea, is the most significant cause of morbidity and mortality in calves less than one-month-old. The major agents of disease causing calf scours are bacterial: E.coli and Salmonella spp., viral: coronavirus and rotavirus, and protozoal: Cryptosporidium parvum. The route of infection is via the ingestion of manure from affected or carrier calves or cows, or contaminated food, water or soil.


E. coli: Common in calves less than 2 weeks of age. Scours due to the F5 (K99) strain of E. coli is most common in calves less than 4 days of age and may cause significant mortalities due to dehydration and electrolyte losses. Scouring is often sudden onset, watery and usually without straining. E. coli is often a secondary invader following rotavirus or Cryptosporidium infection.

Salmonella: The three most common Salmonella serotypes that affect dairy calves under 6 weeks of age are Dublin, Typhimurium and Bovismorbificans. Most properties only have one serotype. Diarrhoea is profuse and varies from watery yellow to haemorrhagic. Sudden death can occur due to septicaemia, dehydration and electrolyte imbalance. Fever is common and calves may die prior to showing signs of illness or scouring.

Rotavirus: One of the most common causes of scours in dairy calves under 6 weeks of age. Diarrhoea is usually sudden onset, watery, white or yellow and may be frothy. While is it usually not fatal, viral diarrhoea can predispose calves to secondary infection with E. coli or Cryptosporidium.

Coronavirus: Typically occurs between ages 5 to 21 days. Dairy effluent can be a major a source of coronavirus. It tends to cause straining and sometimes mucus and blood in the diarrhoea. Recovery can take time, with calves continuing to shed the virus for weeks after scouring stops.


Text Box: Image source: DairyAustralia 2012, ‘Rearing Healthy Calves’ <>



Cryptosporidium parvum: A protozoal organism, it usually occurs as part of mixed scours infections in calves 1 to 4 weeks old. While mortality is generally low, calves can reinfect themselves and develop chronic scouring. Infective eggs can survive in cool soil or water for months to years. Hot, dry weather kills them.


Identifying the cause

Clinical signs alone are not enough to identify the causative organism. In disease outbreaks it is critical that diagnostic testing is done to enable effective control and prevent disease spread and mortalities. ELISA tests are available that enable the detection of rotavirus, coronavirus, E. coli K99 and Cryptosporidium parvum in faecal samples.



Fluid and electrolyte replacement is critical. The main cause of scouring related death is dehydration. Signs of dehydration include an increased skin tent and sunken eyeballs. Oral fluid therapy should be started as soon as clinical signs are evident and may be provided by bottle or tubing. Ensure an electrolyte product designed for calves is used. Look for solutions that contain three key ingredients: glucose, sodium and an alkalising agent such as bicarbonate. Other important components include potassium, glycine or alanine. Generally milk feeding is stopped for the first 24 hours then restarted at intervals greater than 2-3 hours between oral fluids to minimise weight loss and improve recovery. To prevent disease spread, ill calves should be separated and placed in warm and clean housing away from unaffected calves. Veterinary intervention and intravenous fluids are necessary if the calf is not responding to treatment or is recumbent, lacking a suckle reflex or showing neurological signs. Antimicrobial therapy is only indicated for treatment of primary bacterial infections such as E. coli or Salmonella or where there is secondary bacterial overgrowth, invasion and septicaemia. Veterinary advice concerning the need for and most appropriate agent to use is recommended.



Nutrition: Calves should receive at least 2L of good quality colostrum in the first 12 hours of life and an additional 2L before they are 24 hours old. Calves fed whole milk diets have a decreased incidence of diarrhoea. Feeding milk from mastitic quarters or antibiotic containing milk should be avoided as it increases the incidence of scours.

Vaccination: Vaccination of cows in late gestation ensures high levels of antibody are transferred through colostrum to the calves. Vaccines for Salmonella and a combined vaccine for rotavirus, coronavirus and E. coli are both currently available. Vaccination protocols should be aimed at targeting known problematic causes of scours on a property.

Environment and hygiene: Sources of exposure to disease agents include the calving area, cows, contaminated food and water including colostrum, calf housing, people, pets and pests. In cool, damp conditions the main pathogens are all able to survive for weeks to months. Clean housing with good drainage and clean and dry bedding is essential. If kept in groups there should be less than 6 calves to an area. Ideally housing should be based on an impervious material enabling easy decontamination between calf batches. It is essential that all feeding equipment such as nipple buckets be thoroughly cleaned between each feeding.


Salmonella and Cryptosporidium are both able to infect humans and may cause serious disease. Good hygiene and hand washing are essential to reduce disease transmission between calves and also to yourself!




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