Mannan-Rich Fraction Supplementation: A Promising Nutritional Strategy for Optimizing Growth and Health of Pre-Weaning Calves.

The early-stage feeding of calves significantly impacts their lifelong productive performance. During this period, the calves' digestive tracts are in a dynamic state of development, making nutritional regulation a key factor in optimizing their growth potential. This research investigated the influence of mannan-rich fraction (MRF) supplementation on pre-weaning calves. Sixty healthy Holstein calves were randomly divided into a control group and three MRF-supplemented groups (seven males and eight females per group) with low (L-MRF, 2.5 g/calf per day), medium (M-MRF, 5 g/calf per day), and high (H-MRF, 10 g/calf per day) doses. Growth performance, serum biochemical indicators, organ indices, intestinal morphology, and short-chain fatty acid (SCFA) concentrations were measured over a 42-day experiment. Compared with the control group, the M-MRF group had 4.9% higher overall body weight, body length, and starter intake, alongside a reduced diarrhea incidence by 4.6%. At day 14, MRF-supplemented groups exhibited significantly lower Interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) levels, along with significantly higher Interleukin-12 (IL-12), growth hormone (GH), and Immunoglobulin G (IgG) levels. By day 42, IL-6 and Interleukin-1β (IL-1β) levels were also significantly decreased. Additionally, the lung and liver indices were higher and villus height was greater in both the jejunum and colon with MRF supplementation. In terms of SCFAs, the acetate level in the jejunum and the butyrate level in the colon were significantly higher in the MRF-supplemented calves. Both acetate in the jejunum and butyrate in the colon showed a significantly positive correlation with growth performance. Taken together, these findings suggest that MRF supplementation (particularly at 5 g/day) supports calf growth, gut health, and immunity, making it a promising nutritional strategy for pre-weaning calves.