Neonatal calf diarrhoea

What it is

Neonatal diarrhoea is the most common cause of disease and death in calves in their first weeks. The main agents are enterotoxigenic Escherichia coli (ETEC, with F5 or K99 fimbriae), rotavirus, bovine coronavirus and the protozoan Cryptosporidium parvum; mixed infections are common. Other causes are Salmonella, Clostridium perfringens type C, Giardia and errors in milk feeding.

There are two main mechanisms:

• Secretory: ETEC adheres to the small intestinal epithelium and produces an enterotoxin that causes secretion of water and electrolytes without damaging the villi. It mainly affects calves a few days old.
• Malabsorptive: rotavirus, coronavirus and C. parvum destroy the mature enterocytes of the villi, which shorten (villous atrophy). Absorptive surface and enzymes such as lactase are lost, and undigested milk reaching the colon ferments and draws water. They usually affect somewhat older calves, during the first weeks of life.

The consequences are dehydration, metabolic acidosis (from faecal bicarbonate loss and D-lactate accumulation), electrolyte disturbances such as hyperkalaemia, and hypoglycaemia. C. parvum is also a zoonosis for people who handle calves.

Who it affects

Dairy and beef calves under one month of age. The most important risk factor is inadequate transfer of passive immunity from colostrum that is scarce, of poor quality or given late. Others are dirty or wet calving areas and housing, high stocking density, dystocia and, in beef herds with seasonal calving, the build-up of pathogens in the environment as the season progresses.

Anatomy involved

• Small intestine: the main site of infection. ETEC colonises mainly the jejunum and ileum; rotavirus and coronavirus destroy the villous enterocytes; C. parvum lodges in the brush border of the enterocytes, mainly in the distal small intestine.
• Large intestine: coronavirus and C. parvum can also affect the caecum and colon, which worsens diarrhoea because the large intestine cannot compensate for the water loss. Poorly digested milk reaching the colon ferments and increases osmotic diarrhoea.
• Abomasum: in the suckling calf it is the largest compartment of the stomach. Milk that passes through the reticular groove reaches the abomasum directly, where chymosin forms a clot that empties slowly. For this reason it is recommended to keep feeding milk to the diarrhoeic calf: it provides the energy the calf needs and does not worsen the diarrhoea.

Clinical signs

Watery or pasty faeces, yellowish or whitish, sometimes with mucus or blood, and a soiled tail and perineum. Depending on severity: dehydration (sunken eyes, persistent skin tent, dry mucous membranes, cold extremities), weakness, loss of the suckle reflex, inability to stand and recumbency. Acidosis causes depression and ataxia even in mildly dehydrated calves. Severe cases develop hypothermia, coma and death; hyperkalaemia can cause bradycardia and arrhythmias.

Diagnosis

• Clinical: the calf's age points to the agent. The degree of dehydration is estimated from eye recession and skin tent, and the degree of acidosis from the ability to suckle and to stand.
• Faecal tests: on-farm rapid tests for rotavirus, coronavirus, C. parvum and F5 E. coli; PCR; acid-fast stains for Cryptosporidium oocysts; culture for Salmonella.
• Blood tests: blood gases and electrolytes in severely affected calves.
• Herd diagnosis: necropsy of dead calves and monitoring of transfer of passive immunity by measuring serum total protein or Brix in calves 1 to 7 days old.

Treatment and prevention

Treatment is based on correcting dehydration, acidosis and hypoglycaemia. A calf that still suckles receives oral rehydration solutions with alkalinising agents and glucose, while continuing to drink milk. A calf that cannot stand or has lost the suckle reflex needs intravenous fluid therapy with bicarbonate. Antimicrobials are not indicated routinely and are reserved for calves with systemic illness, because of the risk of bacteraemia. Non-steroidal anti-inflammatory drugs may improve welfare. Drug use in calves intended for consumption is subject to national regulations and withdrawal periods.

Prevention relies on:

• Colostrum: sufficient quantity, good quality and within the first hours of life, with routine monitoring of transfer of passive immunity.
• Hygiene: clean, dry calving area, individual housing or small groups, cleaning of feeding equipment and separation of sick calves.
• Vaccination of dams before calving against rotavirus, coronavirus and ETEC, to increase colostral antibodies.
• On farms with cryptosporidiosis, preventive treatment with halofuginone in the first days of life, where authorised.

Key studies

• Lombard et al. consensus (2020): a United States expert group that proposes four categories of passive immunity based on serum IgG: excellent (≥ 25 g/L), good (18–24.9), fair (10–17.9) and poor (less than 10). As a herd goal it proposes more than 40% of calves in the excellent category and less than 10% in the poor one, with equivalents in serum total protein and Brix for use on farm. It rests mainly on United States dairy heifer data and expert opinion.
• Raboisson et al. (2016), meta-analysis of adjusted associations between failure of passive transfer and calf health. Failure multiplied the risk of death by 2.12, of respiratory disease by 1.75, of diarrhoea by 1.51 and of any disease by 1.91. The estimated mean cost was €60 per dairy calf and €80 per beef calf in European systems.
• Bernal-Córdoba et al. (2022), systematic review of trials of antimicrobials for calf diarrhoea: of 2899 studies, only 11 met the criteria, with designs and outcomes so different that a meta-analysis was not possible, and with poor reporting of the trials. It concludes that there is insufficient evidence for the efficacy of antimicrobials in this disease, despite their widespread use.
• Brainard et al. (2021), systematic review and meta-analysis of 25 experiments, mostly European randomised trials, on halofuginone for cryptosporidiosis. Started before 5 days of age, it significantly reduced oocyst shedding, diarrhoea and mortality. Publication bias is possible, especially for diarrhoea outcomes.
• Higgs et al. (2025), systematic review and meta-analysis of dam vaccination against ETEC, with 22 publications. In field trials there was no evidence that vaccination reduced diarrhoea or death in calves under 14 days; in experimental challenge trials, the vaccine prevented death. Field trials were few and of limited quality, and very few reported randomisation, blinding or funding.