The present study was conducted to investigate the effect of thyme oil extract, probiotics or combination of both on the health of suckling calves, growth performance and pathogenic bacteria infection through hematological, biochemical parameters, immune status and fecal examination from birth to weaning. For these purposes, thirty-six newly born Friesian calves were randomly divided into four groups 9 in each. The first group (C) was used as control of which the calves were not supplemented with any additives. The second group (O) included calves received individually 2 ml of thyme oil. The third group (P) included calves received individually 2 gm of probiotics soluble in water. The fourth one (O + P) included calves
received individually 2 ml of thyme oil +2 g of probiotics. All additives were given to calves for 105 days. The results showed that blood total protein, albumin, globulin, AST, ALT, glucose, hemoglobin concentrations, hematocrit values, white blood cells counts, IgG, total oxidants and lysozyme concentrations were positively affected with thyme oil and probiotics
given to calves compared to non-treated calves. Total coliform count, diarrhea incidence and pathogenic bacteria decreased in treated groups with thyme oil and probiotics compared with non-treated ones. Total gain and average daily gain in O+P group were significantly (P<0.05) higher than that of C and P groups through the period from 60th day after birth till the end of experiment. It could be concluded that providing combination of both thyme oil and probiotics for suckling calves was effective in maintaining blood homeostasis, improving general health status and for preventing and treating health problems in suckling Friesian calves.