Scours in Calves: Causes, Treatment & Prevention for Australian Producers

Scours in calves — more formally known as neonatal calf diarrhoea — is the single leading cause of death in beef and dairy calves under one month of age in Australia. On affected properties it can kill 5 to 20 per cent or more of each season's calf crop, with losses skewing heavily toward the first two weeks of life when calves are most vulnerable. Even calves that survive a scours episode often suffer setbacks in growth performance and immune function that persist long after the diarrhoea resolves.

Despite its prevalence, the majority of deaths from calf scours are preventable. The underlying biology of neonatal calf diarrhoea is well understood, the pathogens responsible are identifiable, and the treatments available — when applied early and correctly — are highly effective. What kills most calves with scours is not the disease itself but dehydration and electrolyte loss that go uncorrected because the condition is identified too late or treated inadequately. This guide covers everything Australian beef and dairy producers need to know about causes, clinical recognition, treatment, and prevention of calf scours.

What Causes Scours in Calves?

Neonatal calf diarrhoea is not a single disease but a syndrome caused by a range of different pathogens, often acting in combination. The most important causative agents in Australia are:

Rotavirus

Rotavirus is the most common infectious cause of scours in calves aged 5 to 14 days and is detected in the majority of scours outbreaks investigated in Australian herds. It infects the cells lining the small intestine, causing villous atrophy — flattening and loss of the absorptive finger-like projections — which dramatically reduces the gut's ability to absorb nutrients and fluids. Rotavirus diarrhoea is typically profuse, yellow to pale in colour, and watery. Calves become dehydrated rapidly but often remain bright and alert in early stages. Rotavirus is highly contagious and environmental contamination in calving areas builds up rapidly during a wet calving season.

Coronavirus

Bovine coronavirus affects slightly older calves than rotavirus, typically 5 to 21 days of age, and causes more severe intestinal damage because it affects both the small and large intestine. Coronavirus scours are often more profuse and more likely to contain blood or mucus than rotavirus cases. The virus is highly stable in cold, moist environments, which contributes to its significance in winter-calving operations where calving paddocks become heavily contaminated over consecutive seasons.

Cryptosporidium (Cryptosporidium parvum)

Cryptosporidiosis is caused by a protozoan parasite that is a major cause of calf scours in animals aged 1 to 3 weeks. Unlike viral causes of scours, Cryptosporidium parvum is also a significant zoonosis — it can infect humans, and cases of cryptosporidiosis in farm workers, family members, and veterinarians associated with infected calves are well documented. Standard disinfectants including bleach are largely ineffective against Cryptosporidium oocysts, which makes environmental decontamination particularly challenging. There are limited treatment options specifically targeting cryptosporidiosis in calves beyond supportive care.

Importantly, Cryptosporidium is common in Australian calves and may be significantly under-recognised. Studies of calf scours submissions to diagnostic laboratories routinely identify Cryptosporidium in a high proportion of samples, often in combination with other pathogens.

Escherichia coli (Enterotoxigenic E. coli, ETEC)

Enterotoxigenic E. coli is the most common bacterial cause of calf scours and is most significant in calves under 4 days of age — often causing disease within the first 12 to 48 hours of life. ETEC produces toxins that cause fluid secretion into the gut, resulting in sudden-onset, profuse, watery diarrhoea. Calves can deteriorate from bright and suckling to severely dehydrated and recumbent within hours. ETEC scours is often the most acute and rapidly fatal form of neonatal calf diarrhoea.

The K99 (F5) fimbriae of ETEC strains are the primary virulence factor targeted by commercially available vaccines. Vaccination of cows pre-calving to boost colostral antibodies against K99 E. coli is an effective preventive strategy where this pathogen is confirmed as a significant cause of herd losses.

Salmonella

Salmonella species — particularly Salmonella Dublin and Salmonella Typhimurium — can cause scours in calves of any age but are more common in calves over 2 weeks old. Salmonella scours tend to be more severe, often involving blood and mucus in the faeces, fever, depression, and systemic illness beyond the gut. Salmonellosis in calves requires veterinary attention and antibiotic therapy; it is also a public health concern as multiple Salmonella serovars are zoonotic.

Mixed Infections

It is important to understand that mixed infections involving two or more of the above pathogens simultaneously or sequentially are extremely common. A calf may be infected with both rotavirus and Cryptosporidium, or coronavirus may predispose to secondary bacterial Salmonella infection. Mixed infections are generally more severe and more difficult to manage than single-pathogen cases, and they are one reason why laboratory diagnosis — rather than treatment based on assumed causation — gives significantly better outcomes in outbreak situations.

Why Calves Die from Scours

Understanding why scours kills calves is fundamental to understanding why treatment works when applied correctly and why delay is so costly.

Calf scours kills primarily through three interconnected mechanisms:

1. Dehydration: Diarrhoea causes massive fluid loss far exceeding what a sick calf can replace by suckling. A calf losing 10 per cent of its body weight in fluid (equivalent to about 4 to 5 litres in a 45kg calf) will be severely depressed and on the verge of collapse. At 12 to 14 per cent loss, death is likely without intervention.
2. Electrolyte disturbance: Fluid lost in scours carries with it large quantities of sodium, potassium, chloride, and bicarbonate. The loss of bicarbonate leads to metabolic acidosis — a drop in blood pH that depresses brain function, impairs cardiac output, and causes the profound weakness and inability to stand seen in severely affected calves.
3. Hypoglycaemia (low blood glucose): Sick calves stop suckling, depleting glucose reserves rapidly. A calf that cannot stand and is hypothermic is often significantly hypoglycaemic, and glucose supplementation is essential to its recovery.

The crucial implication of this is that most calves do not die because the pathogen is overwhelming — they die because the fluid, electrolyte, and energy deficits are not corrected. A calf with moderate scours that receives prompt, adequate oral rehydration therapy will generally survive even without specific antimicrobial treatment, while a calf in severe metabolic acidosis that receives no treatment will die regardless of its pathogen load.

Recognising and Assessing Severity

Early recognition and accurate assessment of dehydration severity determines treatment intensity. The key clinical indicators are:

A calf that is bright, alert, and still has a suck reflex can typically be managed with oral electrolytes alone. A calf that is severely depressed, cannot stand, or has lost its suck reflex requires intravenous fluid therapy and urgent veterinary attention — oral fluids alone will not correct the level of dehydration and acidosis fast enough to save these animals.

Temperature is also important: hypothermic calves (rectal temperature below 37°C) require warming in addition to fluid therapy. Do not tube-feed a hypothermic calf that is unconscious — the swallowing reflex may be absent and aspiration risk is high. Warm the calf to above 37°C before oesophageal tube feeding.

Treatment of Calf Scours

Oral Rehydration Therapy (ORT)

Oral electrolyte therapy is the cornerstone of calf scours treatment and is effective for all but the most severely dehydrated calves. Commercial oral electrolyte products formulated for calves contain sodium, potassium, chloride, bicarbonate or acetate (to correct acidosis), and glucose or glycine to facilitate sodium absorption through the gut wall. Not all electrolyte products are equivalent — products designed specifically for calves with adequate alkalinising agent content are substantially more effective than general-purpose electrolyte powders.

The recommended approach for a calf with mild to moderate scours:

• Administer 2 to 4 litres of oral electrolyte solution per treatment, 2 to 4 times per day, depending on the severity of diarrhoea and the calf's ability to suckle
• Continue feeding milk separately from electrolytes — there is strong evidence that continuing milk feeding reduces the duration of illness and supports gut recovery, contrary to older advice to withhold milk
• Space electrolyte and milk feeds by at least 2 hours, since mixing electrolytes with milk impairs curd formation in the abomasum
• Use an oesophageal tube (stomach tube) for calves too weak to suckle from a bottle — this ensures adequate fluid volumes reach the stomach reliably and quickly
• Continue ORT until scouring has resolved and the calf is suckling normally

Intravenous Fluid Therapy

Calves that cannot stand, are severely depressed, or have lost the suck reflex require intravenous fluid therapy as a matter of urgency. IV fluids deliver bicarbonate directly into the bloodstream, correcting metabolic acidosis far faster than oral therapy can in a severely compromised animal. This requires veterinary prescription and ideally veterinary supervision for placement of an IV catheter and administration. Do not delay calling your vet when a calf reaches this level — every hour of delay reduces survival probability.

Antibiotics in Calf Scours

Antibiotics are not indicated for all cases of calf scours and should not be used routinely as a substitute for adequate rehydration therapy. The viral and protozoan causes of scours — rotavirus, coronavirus, and Cryptosporidium — do not respond to antibiotics at all. Antibiotic therapy is specifically indicated when:

• Salmonella infection is confirmed or strongly suspected (systemic signs, bloody faeces, fever)
• ETEC infection is confirmed in very young calves (under 4 days)
• There are signs of systemic septicaemia (fever, rapid deterioration, joint ill)
• The calf is severely immunocompromised or has a compromised gut barrier (bloody diarrhoea with suspected secondary bacterial invasion)

Antibiotic selection should be guided by veterinary advice and, where possible, culture and sensitivity testing. Routine use of antibiotics for all scouring calves contributes to antimicrobial resistance and adds cost without improving outcomes in cases caused by non-bacterial pathogens.

Prevention of Calf Scours

Because treatment of calf scours is labour-intensive and costly, and because even successfully treated calves often suffer growth setbacks, prevention is always preferable to cure. The core prevention strategies operate at three levels: calf immunity, pathogen load, and environment.

Colostrum Management

Adequate colostrum intake in the first 6 hours of life is the single most important determinant of calf survival in the first month. Immunoglobulins absorbed from colostrum provide the newborn calf's only significant passive protection against infectious scours pathogens until the calf's own immune system develops. The practical requirements:

• A minimum of 3 litres of high-quality colostrum within 6 hours of birth; 4 to 6 litres total in the first 12 hours
• Quality colostrum has an immunoglobulin concentration above 50g/L. A Brix refractometer (reading above 22% Brix indicates high-quality colostrum) is an affordable and reliable way to test colostrum quality at the farm gate.
• Colostrum from first-calf heifers is often lower quality than that of cows with prior exposure to the local pathogen environment — consider supplementing heifer calves with high-quality stored colostrum
• Frozen colostrum banks allow you to have quality colostrum available when cows produce inadequate quantities or when a cow dies at calving

Vaccination of Cows

Vaccinating cows and heifers in the 6 to 8 weeks before calving boosts colostral antibody concentrations against specific scours pathogens. Vaccines available in Australia targeting calf scours pathogens include:

• Rotavec Corona (Merck Animal Health): protects against rotavirus, coronavirus, and K99 E. coli. One of the most widely used calf scours vaccines in Australia; requires two doses in unvaccinated cows (4 weeks apart) and an annual booster in subsequent years.
• ScourShield 3 and other rotavirus/coronavirus vaccines: provide protection against the viral causes of scours; choice between products should be made with veterinary advice based on the specific pathogens confirmed on your property.

Vaccination is most cost-effective when the causative pathogens have been confirmed by laboratory testing and a vaccine covering those specific agents is selected. Vaccinating against rotavirus in a herd where scours is primarily caused by Cryptosporidium will not reduce losses.

Calving Environment Management

The concentration of scours pathogens in the calving environment increases progressively as calving season advances. Early-born calves are exposed to a relatively clean environment; late-born calves may face overwhelming pathogen pressure built up over weeks of contamination. Management strategies to reduce environmental pathogen load include:

• The "Sandhill calving system" (clean/dirty paddock rotation): Divide the calving area into multiple smaller paddocks. Move cows with calves under 4 days old into a clean paddock as soon as the calf is strong. Return older cow-calf pairs to a "dirty" paddock. This continuously provides young calves born that day with a relatively clean environment, dramatically reducing early-life pathogen exposure.
• Avoid over-crowding in calving areas: Higher stocking density during calving concentrates faecal contamination and increases infectious dose. Use the largest practical area for calving.
• Shelter from cold and wet: Cold, wet calves are immunocompromised and more susceptible to scours even at low pathogen doses. Providing adequate shelter and wind protection for newborns reduces susceptibility independent of vaccination or colostrum management.
• Disinfection of maternity areas: For dairy operations with housed calving facilities, thorough cleaning and disinfection between calving seasons significantly reduces pathogen carryover. Lime washing of concrete surfaces reduces viral and bacterial loads effectively.

Identifying and Managing Problem Cows

Some cows are persistent carriers of Salmonella or other scours pathogens, acting as a reservoir for infection within the herd. Cows that produce poor-quality colostrum consistently, or that have calves affected by scours in successive years, should be considered for culling from the breeding herd. Similarly, cows with a history of salmonellosis should be managed carefully at calving and their calves monitored closely.

Laboratory Investigation of Scours Outbreaks

When calf scours is causing significant losses on a property — more than 2 to 3 per cent of the calf crop, or when mortalities occur despite apparent adequate treatment — laboratory investigation is strongly recommended. Submitting faecal samples or fresh post-mortem cases to a state veterinary diagnostic laboratory provides pathogen identification that directly guides vaccination, treatment, and prevention strategies.

Without laboratory confirmation, treatment and prevention are based on probability rather than certainty, and resources may be directed at the wrong pathogen. The cost of a diagnostic submission is typically far less than the value of calves lost to an uncontrolled outbreak, or the cost of vaccinating against a pathogen that isn't present on your property.

Summary: Key Principles for Managing Calf Scours

• Colostrum first. Adequate colostrum in the first 6 hours of life is non-negotiable and the single most effective intervention for reducing scours mortality.
• Act early. A calf with scours that is still bright and suckling is relatively easy to save. A calf that has been scouring for 12 to 24 hours without treatment may already be in severe metabolic acidosis.
• Rehydrate, rehydrate, rehydrate. Oral electrolytes are the treatment cornerstone. Give adequate volumes, use good-quality products with alkalinising agents, and continue milk feeding alongside electrolytes.
• Know when to call the vet. Any calf that cannot stand or has lost its suck reflex needs intravenous fluids — oral therapy alone is not enough.
• Don't rely on antibiotics. Most calf scours is viral or protozoal and will not respond to antibiotics. Fluid therapy is the treatment; antibiotics are an adjunct in specific circumstances.
• Reduce environmental contamination. Rotate calving paddocks, avoid overcrowding, and provide clean, dry shelter to reduce the pathogen load new calves encounter.
• Vaccinate cows when indicated. Pre-calving vaccination of cows boosts colostral antibodies against rotavirus, coronavirus, and E. coli. Get laboratory confirmation of pathogens before choosing a vaccine.
• Investigate outbreaks. When scours is causing significant losses, laboratory diagnosis gives you the information to fix the problem rather than manage its symptoms.

This guide is for general information purposes. Calf scours management, antibiotic selection, and vaccination programs should always be developed in consultation with a registered veterinarian familiar with your property and herd.

For more, see our Weaning Calves in Australia: Timing, Methods and Managing the Transition and Sick Cattle Symptoms: 10 Signs That Need Attention on Your Australian Property.