Systematic review of modifiable risk factors shows little evidential support for most current practices in Cryptosporidium management in bovine calves.

Cryptosporidiosis is common in young calves, causing diarrhoea, delayed growth, poor condition and excess mortality. No vaccine or cure exists, although symptomatic onset may be delayed with some chemoprophylactics. Other response and management strategies have focused on nutritional status, cleanliness and biosecurity. We undertook a systematic review of observational studies to identify risk or protective factors that could prevent Cryptosporidium parvum infection in calves. Included studies used multivariate analysis within cohort, cross-sectional or case-control designs, of risk factors among young calves, assessing C. parvum specifically. We tabulated data on characteristics and study quality and present narrative synthesis. Fourteen eligible studies were found; three of which were higher quality. The most consistent evidence suggested that risk of C. parvum infection increased when calves had more contact with other calves, were in larger herds or in organic production. Hard flooring reduced risk of infection and calves tended to have more cryptosporidiosis during warm and wet weather. While many other factors were not found to be associated with C. parvum infection, analyses were usually badly underpowered, due to clustering of management factors. Trials are needed to assess effects of manipulating calf contact, herd size, organic methods, hard flooring and temperature. Other factors need to be assessed in larger observational studies with improved disaggregation of potential risk factors.