Effects of Clostridium beijerinckii-based direct-fed supplementation on growth performance, diarrhea frequency, plasma metabolites, and fecal microbiota of dairy calves.

The high prevalence of diarrhea in calves raises serious welfare concerns and imposes substantial economic losses on dairy farms. Probiotic strains that produce butyric acid may lower diarrhea incidence and improve gut health. This study evaluated the effects of direct-fed Clostridium beijerinckii R8 on growth performance, plasma biochemistry, and fecal microbiota in neonatal calves. Sixty newborn female calves were blocked by birth weight and randomly allocated to 4 treatments: (1) control (0 cfu/d), (2) low dose (1 × 10⁹ cfu/d), (3) medium dose (1 × 10¹⁰ cfu/d), and (4) high dose (1 × 10¹¹ cfu/d). Diarrhea frequency and duration exhibited a significant quadratic response to supplementation, with the lowest values observed at 1 × 10¹⁰ cfu/d. Quadratic treatment contrasts were significant for growth performance. Calves receiving 1 × 10¹⁰ cfu/d achieved the highest BW, ADG, DMI, body diagonal length, and hip width, together with the lowest feed conversion ratio. Plasma total cholesterol, high-density lipoprotein, blood urea nitrogen, and insulin increased linearly with dose. At 28 d of age, immunoglobulin G, immunoglobulin M, total antioxidant capacity, superoxide dismutase, and catalase levels showed linear increases, whereas malondialdehyde declined linearly as dose increased. Fecal microbiota showed both dose-dependent and temporal shifts. On d 28, Lachnoclostridium and Collinsella decreased linearly with dose, whereas Eubacterium_coprostanoligenes_group and Escherichia-Shigella displayed quadratic declines, reaching their lowest relative abundance at 1 × 10¹⁰ cfu/d. By d 56, Lachnospiraceae_NK4A136_group and Intestinimonas increased linearly with dose, while Bifidobacterium and Lactobacillus showed quadratic responses, with their lowest abundance at 1 × 10¹¹ cfu/d. In conclusion, supplementation of 1 × 10¹⁰ cfu/d Clostridium beijerinckii R8 optimally reduced diarrhea, enhanced growth performance, and improved intestinal health by modulating the gut microbiota.