Effects of Colostrum-Period Fecal Microbiota Transplantation on Growth Performance, Immune Function and Gut Microbiota in Pre-Weaned Calves.

Neonatal calf diarrhea caused by intestinal microbial dysbiosis severely restricts rearing efficiency, and fecal microbiota transplantation (FMT) emerges as a promising antibiotic-free strategy for regulating gut homeostasis. Nevertheless, to the best of our knowledge, the effects of colostrum-period FMT and the functional differences between colonic and colostrum delivery routes remain poorly characterized in pre-weaned dairy calves. We hypothesized that colostrum-period FMT would accelerate gut microbiota maturation, improve immune status and reduce diarrhea incidence in pre-weaned calves, with delivery-route-dependent effects. This study aimed to investigate how two colostrum-phase FMT delivery routes shape growth performance, serum immune profiles and gut microbiota in neonatal Holstein calves. Sixty newborn calves were randomly assigned to three groups (n = 20 per group): control (no FMT), colon-FMT (colonic perfusion), and colostrum-FMT (FMT mixed with colostrum). Donor feces were homogenized with sterile saline at a 1:9 ratio for FMT suspension preparation, and the trial lasted 56 days. For growth performance, the colon-FMT calves exhibited significantly higher average daily gain from D29 to D56 (p < 0.05). In terms of intestinal health, the colostrum-FMT group exhibited lower diarrhea incidence during D15-28 (p < 0.05) but markedly higher diarrhea rates during D29-56 (p < 0.01). For serum immunity, colon-FMT calves had elevated serum IgG at D14 (p < 0.05). At D56, the concentrations of IL-2 (p < 0.01) and IL-4 (p = 0.05) were significantly lower in the colostrum-FMT group than the colon-FMT group; no intergroup differences were detected for other serum cytokines and immunoglobulins. 16S rRNA gene sequencing of D28 fecal samples revealed that the colon-FMT group possessed a significantly higher relative abundance of Lactobacillus compared with the other two treatments (p < 0.05). Collectively, colonic FMT is associated with remodeling intestinal microbiota by enriching beneficial Lactobacillus, improved late-stage growth and sustained long-term intestinal health in pre-weaned calves, whereas colostrum-mediated FMT only provides transient protection against early diarrhea.