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Calf diarrhoea – prevention is better than cure


Diarrhoea is the most common cause of death for pre-ruminant calves (one month of age and younger). On-farm research by Teagasc Grange has shown an incident rate for diarrhoea of 8.7% in suckler calves and 25.5% in dairy calves. Calves are particularly vulnerable at this age since the components of the active immune system are under-developed and calves rely on the passive transfer of antibodies from the dam through colostrum. Currently, the best way to manage scours in calves is to prevent it using systemic management practices, strict sanitation procedures and developing a comprehensive herd health plan.

Causes of infectious and non-infectious scours

Scours are classified as infectious when caused by pathogens such as viruses, parasites, and bacteria. They are non-infectious when caused by nutritional stress and poor management practices. Non-infectious scours often leads to infectious scours. Infectious scours frequently manifest as one or more pathogen causing disease. Table 1 summarises scour-inducing agents, the calf age at which it is most likely to occur, and the prevalence of that infectious agent. Scours are generally caused by a viral or parasitic infection. Although less common, bacterial scours often result in severe disease, which can lead to systemic infection.


Rotaviral infection is the number one cause of scours in calves under one month of age in Ireland. It most commonly presents in calves around 5 to 14 days of age. The virus attaches to cells lining the small intestine (epithelial cells), leading to cell death and permanent damage. Eventually, enough epithelial cells will die, leaving the virus without a place to replicate. Calves become infected via faecal-oral transmission. As there are no curative treatments, calves can only be treated using supportive therapies like oral rehydration and anti-inflammatory administration. There is a vaccination that, when given to the dam at the appropriate time-point in gestation, can increase the presence of Rotavirus antibodies.

Table 1. Pathogenic causes of infectious scours

TypeAgent/DiseaseCalf ageOccurrence
Bacteria E. Coli (ETEC) 1 - 5 days Rare
Salmonella spp.  4 - 28 days Less common
Viruses Rotavirus 5 - 14 days Extremely common
Coronavirus 5 - 30 days Less common
Parasites (protozoa)  Cryptosporidiosis (Cryptosporidium parvum 5 - 30 days Extremely common
Coccidiosis (Eimeria spp.) Over 3 weeks Common 


Often referred to as “crypto”, it is a scouring disease caused by the protozoa Cryptosporidiosis spp. In calves, it is almost always caused by the species Cryptosporidium parvum. This is a zoonotic disease, meaning that crypto can be transmitted to humans. It is especially dangerous to young, elderly and immunocompromised humans and animals, so strict biosecurity protocols should always be practiced when working with calves positive for crypto. Like rotavirus there are no curative treatments, only supportive therapies. Halofuginone (Halocur) can be used in prevention, but its therapeutic value is not yet fully understood and use of the product should only be done after consulting with a veterinarian.


It is a common cause of scours in calves reared in pasture environments. It is caused by a parasite in the Eimeria spp. family. Infected calves will often have severe bloody diarrhoea, but it is possible that they show no signs of infection. This parasite uses the small intestine as a breeding ground and has a three week lifecycle, and so is usually seen in older calves. The damage caused by replication in the small intestine has a severe impact on growth and development, even if there are no clinical symptoms. Talk to your veterinarian about getting faecal samples tested if you suspect calves have coccidiosis. If positive, use the coccidiostat prescribed by your veterinarian to treat your calves.

Further information is available at Animal health Ireland who have published very good guidelines on the management of coccidiosis in calves. Bovine Coccidiosis - the facts (pdf) 

Summer Scour Syndrome

This condition is not well understood, and no definitive cause has been determined. Summer Scour Syndrome is used to describe scours in calves that happen shortly after turn out to pasture (within 6 weeks). It presents with the same clinical signs as other scours cases. The traditional scour causes must be ruled out diagnostically before calves can be diagnosed with Summer Scour. The only common factor between calves with Summer Scour is that they are on a grazing diet and it is their first time out to pasture. Immediate removal from pasture helps to resolve the issue. The disease is believed to be associated with rich, lush pastures in combination with an underdeveloped rumen. Consult your veterinarian to rule out all other possible causes of scours in freshly weaned calves at pasture.

Transmission of diarrhoea

Transmission and factors that influence disease manifestation vary depending on the infecting pathogen. Calves become infected by coming into contact with infectious agents in faecal matter (faecal-oral route). In the case of protozoal infections, the environment becomes contaminated by sick calves, ‘healthy’ looking calves, older calves, and adult cattle who shed infectious oocysts in their faeces. Calves, who explore their environment orally, ingest contaminated faecal matter and bring the pathogen directly to their gastrointestinal tract. Pathogens then establish themselves in the gut, causing the lining of the small intestines to become inflamed, in serious cases leading to permanent damage. Inflammation and damage results in malabsorption of nutrients and water in the hindgut and has lifelong ramifications on growth, development, reproduction, and performance.

Diagnosis of diarrhoea

Early detection of diarrhoea is key, so knowing the symptoms is important. Be vigilant for:

  • Increased defaecation; watery/runny consistency; faeces that is brown, grey, green, or yellow in colour; and blood or mucus in the faeces.
  • Weak, depressed, and lethargic calves; with little desire to feed, and a weak suckling reflex.
  • Dehydration: sunken eyes and prominent bony areas (hips, ribs), a staggered or swayed walk, too weak to stand.

Diagnosis of a specific pathogen cannot be done using clinical signs alone. Faecal samples can be tested in a laboratory, or by your veterinarian using a rapid detection test. If calves have died, always send them for post-mortem in order to determine cause of death.


Specific treatments can vary depending on the causative agent. If experiencing a scour outbreak, control the spread and provide supportive therapies to the calves that are ill. No matter the cause of scours, farmers are advised to:

  • ISOLATE sick animals, in a clean, warm, dry space. Remove healthy calves from the contaminated environment. Clean and disinfect everything!
  • HYDRATE scouring calves, dehydration is deadly. Provide supplemental electrolyte feedings between milk meals to keep calves hydrated.
  • Keep FEEDING sick calves their milk meals, the nutrients in milk helps fight disease.
  • Keep the calf comfortable by providing clean, deep bedding, and use of calf jackets.

Further information is available on the Animal Health Ireland website  

At no point should antibiotics be used to treat scours if there is no indication of bacterial infection. Bacteria are one of the least common causative agents of scours in calves. The use of antibiotics, if there is no sign of bacterial infection, only increases antimicrobial resistance leading to less effective drug therapies and more severe disease. As always, talk with your veterinarian about which courses of action are best for your situation.


Herd Health Plan

There are many different aspects to prevention that are key to managing scours. Calf husbandry management, biosecurity protocols and vaccination programs are all essential and can be managed systemically through the development and use of a comprehensive herd health plan. The herd health plan should focus on the different parts of the cattle production system and how these parts interact with each other. Consulting with your veterinarian and livestock advisor is critical when developing a comprehensive herd health plan. With regards to calf health and preventing scours, a major component of this health plan should focus on optimizing colostrum management.

Colostrum, or first milk, not only provides essential nutrients to the calf in the first hours of life, it also allows for the passive transfer of antibodies needed for the calf to protect itself prior to the full development of an active immune system around 3-4 weeks of age. Ensuring that your calves receive adequate amounts of quality colostrum quickly helps them get the best start in life. You can easily measure the quality of colostrum using a Brix refractometer.

Animal Health Ireland recommend that producers follow the 1 > 2 > 3 method of colostrum feeding for dairy calves:

1) Calves are fed the colostrum from the FIRST milking on their FIRST feed.

2) Calves should be fed their colostrum within TWO hours of birth.

3) Make sure calves get at least THREE litres of colostrum.

Implementing the 1-2-3 approach with suckler beef calves would not be practical. Hence, colostrum management programmes on suckler beef farms need to emphasize the importance of colostrum quality and the timing of colostrum ingestion, and how these factors can be manipulated and monitored by the farmer. The calf’s small intestine has the ability to absorb immunoglobulins (Ig) during the first 24 hours of life, but the efficiency of absorption begins to decline within a few hours of birth. Failure of passive transfer (FPT) of immunity occurs when the calf does not absorb sufficient Ig within this time period. It is well established that calves with FPT are at greater risk of morbidity and mortality, begin exhibiting clinical signs of disease at younger ages, and experience an increased number of sick days and reduced growth performance when compared to calves with adequate passive immunity. Cattle develop immune systems specific to their environment which means the colostrum they produce will be tailored to the potential pathogens that are already present in the environment. There are vaccinations for E. coli, Rotavirus, and Coronavirus. Vaccinating dams for these diseases at the correct time-point in gestation helps increase antibodies in the colostrum, which protects the calf while the immune system develops. Work with your veterinarian to develop a vaccination program that is appropriate for your farm. 

Sabine Scully, Bernadette Earley and Sinéad Waters

Teagasc, Grange Animal & Grassland Research and Innovation Centre, Dunsany, Co. Meath

The ‘Holoruminant’ EU-funded Project:

Ongoing research continually improves our understanding of specific infectious diseases and management practices. Teagasc, as a part of the EU-funded Holoruminant project, is working to uncover links between early-life microbiomes and manifestation of scours in calves. The information uncovered will set up the foundations needed for alternative and holistic scour management. The development of alternative and holistic management strategies will create opportunities to develop more sustainable bovine production systems.