Calf scours: differentiating by age and preventing it

Neonatal diarrhoea is the leading cause of loss in calves during the first months of life. Many different agents produce a similar picture, but they differ in the age at which they appear — and that is the most practical starting point for differentiating them in the field.

Likely agents by age of onset

Age of onset	Agents to consider first
1–5 days	Enterotoxigenic E. coli (ETEC)
5–15 days	Rotavirus, coronavirus
5–28 days	Cryptosporidium parvum
3 weeks onwards	Eimeria (coccidiosis); Salmonella at any age

These ranges are not hard boundaries, and mixed infections are more the rule than the exception in the field. Even so, the age at which scouring first appears narrows the list of agents worth investigating considerably.

Enterotoxigenic E. coli acts very early. It attaches to the intestinal epithelium and the toxin it secretes drives fluid loss into the gut lumen.

Rotavirus and coronavirus destroy the mature cells at the tips of the small-intestinal villi. Absorptive surface and digestive enzymes are reduced; undigested milk remains in the gut and causes an osmotic diarrhoea.

Cryptosporidium parvum damages villi in a similar way. It carries additional significance because it is zoonotic: hand hygiene and protective equipment matter for anyone handling affected calves.

Salmonella usually produces a more severe picture, with fever, blood and mucus in the faeces and signs of systemic disease.

The real danger: fluid and electrolyte loss

In calf scours, death usually results not from the agent itself but from dehydration and metabolic acidosis. What is lost is not only water: sodium, potassium and bicarbonate go with it.

Supportive fluid and electrolyte therapy therefore takes precedence over any agent-directed approach. Assessing the degree of dehydration — skin tent, eyeball recession, suck reflex, ability to stand — guides treatment. That assessment and the treatment given are veterinary decisions.

A common mistake is withdrawing milk entirely from a scouring calf. Milk is the calf’s energy source, and withdrawing it delays recovery. Current practice is to continue milk and give electrolyte solution as separate feeds. Agree the regime with your veterinarian.

Colostrum: the single most effective measure

Because of the structure of the bovine placenta, a calf is born without antibody from its dam. Its immunity comes entirely from colostrum.

Effective colostrum management has four components:

• Quality — high antibody content, measurable with a colostrometer or Brix refractometer.
• Quantity — a sufficient volume relative to the calf’s bodyweight.
• Timing — the gut’s ability to absorb antibody declines rapidly after birth, so the first hours are critical.
• Hygiene — colostrum with a high bacterial load both impairs antibody absorption and delivers pathogens directly.

A calf that does not receive enough antibody has failure of passive transfer, which leaves it markedly more susceptible not only to scours but to respiratory disease as well.

Other preventive measures

Calving-area hygiene. Most of these agents transmit by the faecal-oral route. A clean, dry calving area reduces the initial infective dose.

Calf housing. Individual pens or small groups, dry bedding, and an environment that is ventilated but free of draughts all limit transmission.

Separating age groups. Older calves can be a source of infection for younger ones.

Equipment hygiene. Milk buckets, teats and especially oesophageal feeders carry pathogens directly if they are not cleaned.

Vaccinating the dam. For some agents, vaccinating the cow during the dry period raises specific antibody in colostrum. Whether such a programme is appropriate depends on the region and the farm’s history.

When does it need a diagnosis?

Diarrhoea in one calf is a case; recurring diarrhoea across the herd is a management problem. Where scours recurs, identifying the agent from faecal samples directs both the right treatment and the right preventive measure — because viral, bacterial and parasitic agents call for different strategies.

Plan treatment and prevention with the veterinarian who knows the operation.