ABSTRACT Megasphaera elsdenii converts lactate and glucose into butyrate, the main volatile fatty acid responsible of papillae development and may benefit calf performance. Twenty-six Holstein calves (BW = 34.5 ± 1.65 kg) were randomly assigned at birth to a control group (Meg0) and a group that received an oral dose of M. elsdenii NCIMB 41125 at 14 d of age (Meg14). Calves received colostrum for the first 3 d followed by free choice access to whole milk until weaning at 56 d. From d 4 onward, starter and water were offered ad libitum. Intakes were measured daily and body weights (BW) weekly. Blood samples were collected on day 7, 21, 28, 42, and 56 for β-hydroxybutyrate (BHBA) analysis. Performance was measured for an additional 14 d post-weaning. Pre-weaning milk intake was lower (p = 0.010) and starter DMI (dry matter intake) greater (p = 0.001) for Meg14 than Meg0 calves. Total DMI, metabolisable energy (ME) intake and average daily gain (ADG) were similar (p > 0.05) for both groups, but Meg14 calves had greater weaning BW (p = 0.012) and feed efficiency (p < 0.029). The average BHBA between d 21 and 56 was greater for Meg14 (p = 0.03) compared to Meg0 calves. After weaning, Meg14 calves had greater DMI (p = 0.027), ME intake (p = 0.023) and ADG (p = 0.002) and tended to have better feed efficiencies (p = 0.07) than Meg0 calves. Administering M. elsdenii NCIMB 41125 improved starter intake and feed efficiency, which was associated with high blood BHBA.