Twenty Lithuanian Black-and-White calves (10 bulls, 10 heifers) were used to evaluate the effects of the supplemental probiotic product, Enterococcus faecium M74 (2.4 g/day/calve), added to fresh milk and skimmed milk in a 56 day-study. The probiotic was administered by dietary supplementation to first group of calves and their respective pens (probiotic group), whereas the second group (control group) received no probiotic supplementation. The results of this trial indicate positive effects of the probiotic product Enterococcus faecium M74. The actual percentage of calves with diarrhoea was reduced from 50 % to 20% among the calves fed the pre-and probiotic diet. Probiotic supplementation reduced the faecal count of clostridia and enterococci. The calves fed Enterococcus faecium M74 weighed more at 20, 40 and 62 days of age by 4.9%, by 9.7% (P < 0.05) and by 9.4% (P < 0.01), respectively, than the control calves. The calves fed Enterococcus faecium M74 had increased daily weight gains compared with the calves not fed a probiotic product. The average weight gain and the daily weight gain of the probiotic-supplemented calves were by 7.8 kg (P < 0.01) and by 0.14 kg higher (P < 0.01) compared with the control calves. The calves given the Enterococcus faecium M74 also had forage and total DM intakes that were numerically higher than those fed the control diet, without any additive. During the 56 days experimental period, the average feed conversion rate was improved by 12.9% in the probiotic-treated group.