Various prebiotic and plant feed additives claim to promote growth and proper development of the gastrointestinal tract by different modes of action. Objective of this study was to compare the effects of 2 feed additives for milk replacers on growth and feed conversion of dairy calves. The trial was conducted from October 2015 to May 2016 in North-Western Germany with 80 female Holstein rearing calves of one dairy herd. At d 4 postpartum (BW 44.9 ± 5.2 kg) calves were assigned to 2 treatment groups (A and B). Calves of group A were fed a milk replacer (160 g per liter) enriched with a prebiotic preparation (0.3% dry powder) of calcium gluconate, calcium and sodium carboxylates, fructooligosaccharides (scFOS) and a plant extract (AntaTop MAT, Dr. Eckel Animal Nutrition, Germany). The milk replacer of group B contained a mixture of a plant extract rich in benzophenanthridine alkaloids and organic acids (0.3% dry powder). Milk replacer intake was measured individually (n = 80). Calf starter feed was offered from d 14 (max. Two kg/calf/day) and roughage from d 21 (ad libitum). Body weight was measured at d 4, 14, 40 and 64 postpartum. Data were analyzed using ANOVA (IBM SPSS). During the main feeding period (d 14 - 40) daily weight gain was significantly higher (P < 0.05) in group A (prebiotic) (927 ± 181 vs. 821 ± 252 g/d). Daily weight gain over the whole period (d 4 - 64) was not statistically different (P < 0.05) between treatments A and B (878 ± 119 vs. 860 ± 137 g/d). Calves of group A needed 5.6 kg (±1.58) less (P < 0.01) milk replacer powder (72.0 vs. 66.4 kg) to achieve this weight gain. Consequently, feed conversion of milk replacer into body mass was significantly lower (P < 0.01) in the prebiotic group (A) than in the alkaloid group (B) (1.28 ± 0.22 vs. 1.41 ± 0.21 kg/kg). Calves of the prebiotic group (A) consumed more roughage (45.8 ± 6.9 vs. 41.7 ± 11.6 kg dry matter) and more calf starter feed (15.2 ± 3.5 vs. 10.9 ± 3.9 kg dry matter). Differences in roughage and starter intake were not significant (P > 0.20). The results indicate that efficiency of dairy calf feeding can be improved by a prebiotic additive in milk replacer.