Supplementing sialyllactose to colostrum replacer improved intestinal health and blood immunity by affecting the abundance of intestinal bacteria in dairy calves

Sialyllactose (SL) and its derivatives possess various nutritional and biological benefits for mammals, whereas its effects on dairy calves have not been well characterized. This study evaluated the effects of SL supplementation to colostrum replacer on growth performance, blood immune parameters, intestinal development and microbial composition of preweaned dairy calves. Fifty-six newborn Holstein calves were randomly allocated to either a control group (CON; n = 28; 17 males, 11 females) receiving colostrum replacer without SL supplementation, or a treatment group (CSL; n = 28; 17 males, 11 females) receiving colostrum replacer with SL supplementation. Subsequently calves were fed milk replacer. Starter was provided from d 3. Data on feed intake, feces scores, and disease treatment were recorded daily from d 1 to d 56. Body weight and body size were measured on d 0 (after birth immediately), 14, 28, 42, and 81. Blood samples were collected on d 1 (>24 h), 7, 28, and 56. Fecal samples were collected on d 7 and 28. To analyze intestinal morphology and gene expression, 6 bull calves in each group were harvested at 7 d of age. The results showed that SL administration increased starter DMI. The body weight, heart girth and withers height of the calves in CSL group tended to be higher than those in CON group. The SL administration affected the inflammatory cytokines in serum by increasing interleukin-6 and haptoglobin protein (HPT) on d 1 and interleukin-1β, tumor necrosis factor-α (TNF-α) and HPT on d 7, then decreasing interleukin-1β and TNF-α on d 28 and interleukin-6, TNF-α, c-reaction protein, serum amyloid A and HPT on d 56. The SL administration resulted in higher diamine oxidase in serum on d 7. The SL supplementation elevated the expression of ZO-1 in jejunum epithelial cells. Supplementing SL affected the intestinal microbiota by increasing the abundances of Erysipelotrichaceae_UCG-003, Bacteroides, Parasutterella, Sutterella, Actinomyces, Megamonas, and Sharpea, and decreasing the abundances of Klebsiella, Fusobacterium, Gastranaerophilales, Colidextribacter, and Desulfovibrio. Lactobacillus prophage enriched in the intestine of CSL group calves on d 28 had a negative correlation with IL-1β, IL-6, TNF-α, serum amyloid A, HPT, diamine oxidase and D-lactic acid in serum. In conclusion, supplementing SL in colostrum replacer may promote the growth and health by increasing starter intake, improving the barrier of intestine, and changing the abundance of intestinal bacteria in calves. © 2025, The Authors.