peer reviewed ; The purpose of this study was to evaluate, under field conditions, the efficacy of an european registered bovine concentrated lactoserum (Locatim) in 3 farms with neonatal diarrhoea in calves. A total of 117 healthy Belgian Blue (BB) calves were allocated in 2 groups. Two thirds of the calves received Locatim orally immediately after birth and maternal colostrum one hour later (treated group), while control calves only received maternal colostrum. Every day during 14 days, mental status, faeces consistency, suckling reflex and hydration status of each calf were monitored. Individual blood samples were assessed for passive transfer and specific Escherichia coli antibodies against strains F5, CS31A, F17 and F41. Faecal samples from diarrheic and non diarrheic calves were analysed for rotavirus, bovine coronavirus, Cryptosporidium parvum and Escherichia coli F5. Locatim had no significant effect on the onset, duration and incidence of diarrhoea. The mean serum IgG concentration of 23.1 ± 7.8 mg/ml indicates a good IgG transfer. Only the CS31A strain titer was significantly higher in the treated group. The major identified causative agent of diarrhoea was C. parvum. In conclusion, Locatim only has a slight effect when IgG transfer is optimal, but could be justified when specific antibodies lacking in colostrum are needed