Calf Scours in Cows' Calves: Causes, Dehydration Signs, and Treatment

Calf scours is the common term for diarrhea in young calves, especially during the first month of life. It is not one single disease. Instead, it is a syndrome with many possible infectious and management-related causes. Some calves stay bright and continue nursing, while others decline very quickly.

The main danger is fluid loss. As diarrhea worsens, calves can lose water, sodium, potassium, bicarbonate, and energy. That can lead to dehydration, metabolic acidosis, weakness, recumbency, and death. Merck notes that severe neonatal diarrhea can become life-threatening in as little as 12 hours.

Scours is also one of the most important causes of illness and death in calves under one month old. Because several pathogens can look similar early on, your vet usually focuses first on stabilizing the calf with fluids and electrolytes, then on narrowing down the likely cause and herd-level risk factors.

For pet parents and producers alike, the key message is speed. A calf with diarrhea that is still standing and willing to suck often has more treatment options than a calf that is already down, cold, or mentally dull.

Calf scours usually develops from a mix of pathogen exposure, calf immunity, and environment. The most common infectious causes in many areas are enterotoxigenic Escherichia coli, rotavirus, coronavirus, and Cryptosporidium parvum. Salmonella can also cause diarrhea and may be more severe because it can involve systemic illness. In somewhat older calves, coccidia can become an important cause, especially where stocking density and manure contamination are high.

Age matters. E. coli tends to affect very young calves, while crypto is especially common in calves about 1 to 3 weeks old. Salmonella and coccidiosis are often seen in older calves, though there is overlap. Mixed infections are common, and those calves often have longer-lasting diarrhea and a higher risk of weight loss or death.

Management factors are just as important. Failure of passive transfer from poor-quality, delayed, or contaminated colostrum raises the risk of severe disease. Cornell notes that calves should receive colostrum within 2 to 4 hours of birth, and that feeding poor-quality or bacteria-contaminated colostrum increases scours risk. Crowding, dirty bedding, wet calving areas, contaminated bottles or buckets, stress, and abrupt feed changes can all increase disease pressure.

Not every case is infectious. Overfeeding, inconsistent milk mixing, sudden diet changes, and other digestive upsets can contribute to osmotic diarrhea. Your vet may also consider septicemia, ruminal drinking, or other neonatal problems if the calf looks much sicker than the diarrhea alone would suggest.

Diagnosis starts with the calf in front of your vet. They will assess age, nursing history, temperature, hydration, attitude, suck reflex, manure appearance, and whether the calf can stand. This first exam often matters more than the exact pathogen on day one, because fluid loss, acidosis, and weakness need treatment right away.

Your vet may estimate dehydration by looking at eye position, gum moisture, skin tent, limb temperature, and mentation. They may also check whether the calf is acidotic or hypoglycemic based on the exam or bloodwork. In more serious cases, blood tests can help guide fluid choice and show electrolyte changes, acid-base imbalance, or evidence of sepsis.

To identify the cause, your vet may recommend fecal testing such as antigen tests, ELISA, flotation, or PCR panels, depending on the calf's age and the herd situation. These tests can help detect rotavirus, coronavirus, Cryptosporidium, E. coli, Salmonella, or coccidia. If several calves are affected, herd-level history becomes very important, including colostrum practices, sanitation, housing, vaccination plans, and recent weather or stressors.

Because more than one pathogen may be present, a diagnosis is often both individual and herd-based. In other words, your vet is not only asking, "What is making this calf sick today?" but also, "Why are calves in this environment getting sick now?"

Prevention starts with colostrum. Calves need enough clean, high-quality colostrum early, because delayed or poor transfer of maternal antibodies raises the risk of severe diarrhea and death. Cornell recommends feeding colostrum within 2 to 4 hours of birth, and many herd programs also monitor colostrum quality and cleanliness because bacterial contamination can increase scours problems.

Cleanliness matters every day, not only at calving. Keep calving areas dry, remove manure often, clean bottles and nipples thoroughly, and avoid crowding young calves. Crypto oocysts can survive for months in cool, moist environments and resist many disinfectants, so moisture control, manure management, and reducing calf-to-calf exposure are especially important.

Work with your vet on herd-level prevention. That may include reviewing dam vaccination plans, newborn handling, colostrum storage and testing, pen design, and treatment protocols for early cases. A written plan helps everyone respond faster when the first loose stool appears.

Nutrition and consistency also help. Mix milk replacer accurately, avoid abrupt feed changes, provide clean water, and reduce stress from transport, weather, and housing changes when possible. Good prevention does not remove all risk, but it can lower the number of sick calves and reduce how severe outbreaks become.