BACKGROUND: Heat treatment of colostrum has been suggested as a control measure to eliminate or reduce the transfer of colostrum-borne pathogens to dairy calves.Objectives: The aims of this study were to determine the effects of on-farm heat treatment of bovine colostrum on colostral bacterial counts and IgG concentration and evaluation of passive transfer of immunity in neonatal dairy calves. Methods: Ninety-six L of first milking colostrum was collected from Holstein cows and pooled to create a uniform batch. Twenty-four calves were enrolled in 4 treatment groups before suckling occurred and fed raw colostrum (n=6), heat-treated colostrum at 60 ºC for 30 min (n=6), heat-treated colostrum at 60 ºC for 60 min (n=6) and heat-treated colostrum at 60 ºC for 90 min (n=6). Colostrum samples were collected before and after heat treatment and cultured for total bacterial count and analyzed for total IgG concentration. For the first and second feeding 2 L of colostrum was bottle fed by 2 and 12 h of age respectively. Serum samples were collected from calves at 0 h (precolostrum) and 6, 24, 48, 72 h (postcolostrum) and analyzed for serum total protein and IgG concentrations. Results: Heat treatment of colostrum at 60 ºC for 30 and 60 min reduced total bacterial count, yet maintained colostrul IgG concentration compared to the control. There was no difference between treatment groups when examining serum total protein and IgG concentrations, but apparent efficiency of IgG absorption was significantly greater at 6 h in calves that were fed heat-treated colostrum compared to calves fed raw colostrum. ConclusionS: There was no effect of on-farm batch heat treatment of colostrum at 60 ºC till 90 min on serum concentration of IgG.