Passive transfer of immunity, a key component of animal health in early life, is primarily the result of immunoglobulin (IgG) production in the dam and IgG absorption in the calf. This study examined the effect of supplemental butyrate on serum IgG concentrations in late pregnancy dams and their calves. Twenty multiparous Holstein dams were fed a close-up TMR ad libitum and assigned either a control treatment (DAM-C) or a butyrate treatment (DAM-B). Dams in the DB treatment were fed butyrate daily at a rate of 1% of DMI, mixed into the TMR, from 3 wk prepartum until calving. Until calving, DMI was measured daily and blood serum was sampled weekly. At calving, colostrum was sampled and analyzed for IgG. At birth, calves were assigned to either a control (CALF-C) or a butyrate treatment (CALF-B). Within 2 h of calving, all calves were fed one gallon of colostrum replacer; colostrum fed to CALF-B calves was supplemented with butyrate at 2.5% wt/vol. Weekly, calves were weighed and blood was sampled for determination of average daily gain and serum IgG, respectively. Data were analyzed using PROC MIXED in SAS with the fixed effect of treatment, random effect of animal, and, where applicable, fixed effect of week as a repeated measure. In dams, there was no difference in DMI between DAM-C and DAM-B treatments (25.0 ± 3.2 vs. 24.1 ± 2.1 kg/d, respectively; P = 0.77). Serum IgG concentration in dams was not different between the DAM-C and DAM-B treatments (1785 ± 117 vs. 1736 ± 137 mg/dL, respectively; P = 0.79). Colostrum IgG levels were also unchanged between DAM-C and DAM-B treatments (160.3 ± 72.09 vs. 117.45 ± 35.09 g/L respectively; P = 0.46). In calves, serum IgG levels were higher in CALF-C than in CALF-B treatments (1489 ± 71 vs. 997 ± 63 mg/dL, respectively; P < 0.01). Calf average daily gain did not differ between CALF-C and CALF-B treatments (0.54 ± 0.05 vs. 0.49 ± 0.05 kg, respectively; P = 0.43). In dams, feeding supplemental butyrate did not impact DMI, serum IgG concentration, or colostrum IgG concentration. In calves, supplemental butyrate had detrimental effects on serum IgG concentration, adversely affecting passive transfer of immunity.