By Vet Paul Kirkwood
Scour caused by Cryptosporidium parvum remains one of the most common and costly infectious diseases of calves in the UK. Damage can manifest as acute clinical signs including dehydration, lethargy, anorexia, weakness and increased mortality, and there are also longer-term impacts with reduced growth rates and compromised productivity later in life.
Calves are most at risk of cryptosporidiosis in the first two weeks of life, with clinical cases usually occurring at 7–14 days, although infection can occur outside this timeframe. The parasite is shed in large numbers in faeces, and the oocysts are immediately infectious and highly resilient in the environment. High infection pressure arises where young calves are overstocked, bedding remains moist and cleaning-and-disinfection is inadequate.
The mainstay of any scour-prevention strategy is prompt, adequate ingestion of high-quality colostrum. Good colostrum intake improves general immunity and helps calves deal with a variety of scour-causing pathogens including C. parvum.
Targets for dairy and beef calves include feeding at least 3–4 litres of colostrum (10% of bodyweight) within 6 hours of birth. If possible, continue transition milk (or equivalent colostrum feedings) for the first 2–5 days. Monitor colostrum quality (e.g., using a Brix refractometer and feeding only colostrum >25%). Ensure calves have adequate serum total protein levels via blood sampling at 2–7 days of age. Successful passive transfer of immunity helps calves cope with the C. parvum challenge.
However, colostrum alone is not enough if environmental infection pressure is high.
Because C. parvum oocysts survive well in moist, dirty environments and resist many common disinfectants, housing and management must be robust. By reducing the oocyst load and improving calf immunity, the chance of clinical disease decreases.
Key practical steps include using an “all-in/all-out” approach: calves should enter clean pens that have been thoroughly mucked out, cleaned, disinfected and dried before the next batch arrives. Choose disinfectants proven effective against cryptosporidial oocysts and ensure correct contact time, temperature and drying.
Ensure bedding is dry, well drained and free from pooled water, slurry or contaminated areas. Calves lying in soiled bedding are at high risk of exposure. Elevate feed and water troughs (~0.75 m) to reduce faecal contamination. Clean and disinfect calf jackets, boots, feeding equipment and pens between calves or groups; jackets in particular can harbour oocysts if wet or reused without cleaning.
On beef units, manage the calving paddock to minimise faecal loads, use clean bedding, isolate sick calves, and avoid mixing age groups, as older calves shed infection and increase pressure on younger animals.
In August 2024 the first vaccine to help control cryptosporidiosis in calves was launched in the UK. The vaccine is given to pregnant heifers and cows in the third trimester. It contains C. parvum antigen, prompting the dam to generate antibodies that are concentrated in colostrum. When the newborn calf ingests that colostrum (and transition milk), it receives passive immunity from birth. The vaccine does not replace good colostrum management, hygiene or housing, and the duration of proven immunity in the calf is up to around two weeks.
The primary course is two doses, 4–5 weeks apart in the third trimester, finishing at least three weeks before expected calving. A single annual booster is required to enhance colostrum in subsequent dry periods. The vaccine works best as part of a herd-level strategy; vaccinating all pregnant cows and heifers reduces overall infection pressure. It will reduce clinical signs (diarrhoea) caused by C. parvum and decrease environmental oocyst shedding, but it will not eliminate all risk of cryptosporidium.