Thirty calves were randomly assigned to two treatments and fed until weaning [42 days (d) of age]. Treatments were a control group (n = 15), which did not receive Megasphaera elsdenii (Me0) and a M. elsdenii group, which received a 50-ml oral dose of M. elsdenii NCIMB 41125 (10(8) CFU/ml) at day 14 day of age (Me14). Calves were given colostrum for the first 3 day followed by limited whole milk feeding. A commercial calf starter was offered ad libitum starting at day 4 until the end of the study. Fresh water was available throughout the study. Feed intake and growth were measured. Blood samples were collected via jugular venipuncture to determine β-hydroxybutyrate (BHBA) concentrations. Fourteen male calves (seven per group) were euthanised on day 42 and digestive tracts harvested. Reticulo-rumen weight was determined and rumen tissue samples collected from the cranial and caudal sacs of the ventral and dorsal portions of the rumen for measurements of papillae length, papillae width and rumen wall thickness. Dosing with M. elsdenii NCIMB 41125 improved starter dry matter intake (DMI), weaning body weight (BW) and tended to improve average daily gain. Calves in Me14 group had greater plasma BHBA concentration than Me0-calves during the last 3 weeks of the trial and had at day 42 greater reticulo-rumen weight, papillae width and papillae density compared to Me0. No differences in rumen wall thickness or papillae length were observed between the two groups. Total volatile fatty acids, acetate and propionate production did not differ between treatments, but butyrate production was greater in Me14 than Me0. Dosing M. elsdenii NCIMB 41125 showed benefit for calves with improved feed intake and rumen development suggesting increased epithelium metabolism and improved absorption of digestive end products.

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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.

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