Ad libitum milk replacer (MR) feeding and butyrate (B) have independently shown that both stimulate postnatal growth in dairy calves. We hypothesized that the combination of intensive MR feeding and B supplementation accelerates body growth and the maturation of the somatotropic axis in a synergistic manner in preweaning calves. Holstein calves (32 male and 32 female) were studied from birth until wk 11 of age. All calves received colostrum and transition milk until d 3 of age and from d 4 onwards calves were fed MR in amounts of either 6 L/d (Res; n = 32) or ad libitum (Adl; n = 32) for 8 wk. In both feeding groups half of the calves were fed MR with 0.24% B or same MR with no B supplement. From wk 9 to wk 10 MR was linearly reduced in all calves to 2 kg/d. Hay, water, and concentrate (CON) were offered ad libitum. Feed intake was measured daily and body weight (BW) weekly. Blood samples for analyzing IGF-I, IGF binding proteins (IGFBP), insulin, and glucose were taken on d 1, 2, 4, and 7, then weekly or biweekly (IGFBP) until wk 11 of age. Liver samples were taken on d 50 and at the end of the study (d 80 of age) to measure gene expression of the somatotropic axis. Data were analyzed by the Mixed Model of SAS with MR feeding, B supplementation, time, and sex as fixed effects. MR consumption and BW were greater, but CON intake was lower in Adl than in Res groups (P < 0.001). Plasma concentrations of IGF-I, IGFBP-3, insulin, and glucose were greater (P < 0.01) and plasma concentration of IGFBP-2 was lower (P < 0.05) in Adl than in Res. B supplementation depressed (P < 0.05) plasma IGF-I from wk 1–4 and in wk 9. On d 50, mRNA abundance of the growth hormone receptor and IGF-I was greater (P < 0.02) and of IGFBP-2 mRNA was lower in Adl than in Res. At the end of the study, IGFBP-2 mRNA was greater in Adl than in Res and increased by B. Ad libitum MR feeding stimulated the systemic and hepatic somatotropic axis, and mirrored the greater growth rate during the intensive MR feeding. Butyrate supplementation did not stimulate growth performance but partly depressed the IGF system.