Impact of Saccharomyces cerevisiae boulardii CNCMI-1079 and Lactobacillus acidophilus BT1386 on total lactobacilli population in the gastrointestinal tract and colon histomorphology of Holstein dairy calves

There is interest in the use of direct-fed microbials (DFM) as substitutes for antibiotic growth promoters in farm animal production. However, little information exists on their effects in dairy calves. The aims of this study were to: 1) determine the viability of supplemental DFM in feed and throughout the gastrointestinal tract (GIT) of calves; 2) evaluate the effect of DFM on total lactobacilli population in the digestive tract and in feces of calves; and 3) examine the influence of DFM on colon histomorphology and overall calf performance. Forty eight calves (2-7 days old) were randomly allocated to four treatments as follows: 1) Control (CTRL) fed milk replacer (MR) followed by starter feed (SF); 2) CTRL supplemented with Saccharomyces cerevisiae boulardii CNCMI-1079 (SCB; 7.5 × 108 colony forming units (CFU)/L MR + 3 × 109 CFU/kg SF); 3) CTRL supplemented with Lactobacillus acidophilus BT1386 (LA; 2.5 × 108 CFU/L MR + 1 × 109 CFU/kg SF); and 4) CTRL supplemented with antibiotics (ATB) chlortetracycline and neomycin (528 and 357 mg/L MR, respectively), and chlortetracycline (55 mg/kg SF). Four calves per treatment were euthanized on day 33 (pre-weaning) and an additional four calves per treatment on day 96 (post-weaning) to sample different sections of the GIT. The effects of treatments were analyzed following a completely randomized design with repeated measures and Tukey adjustments for multiple comparisons. The DFM (SCB and LA) remained viable in the commercial product throughout the period of the experiment. Viable SCB was recovered throughout the GIT and in the feces pre- and post-weaning. There was no effect of DFM on total lactobacilli population in the GIT of calves. However, feces of SCB-treated calves showed a greater lactobacilli population compared with CTRL (P < 0.01) around weaning. In the pre-weaning period, the distribution of lactobacilli population differed along the digestive tract (colon > ileum content > rumen > ileum mucosa; P < 0.001). The lactobacilli population was significantly reduced in all compartments (P = 0.02) post-weaning compared to pre-weaning, except in the rumen. Crypts depth and width of the colon decreased (P < 0.01) whereas number of goblet cells containing neutral mucins tended to increase (P = 0.058) while acidic mucins increased (P < 0.05) in SCB- and ATB-treated calves compared with CTRL and LA-treated calves. Overall, growth performances were not affected by treatment. Feeding SCB stimulated total lactobacilli population around weaning and altered colon morphology with potential beneficial effects during the early period of growth in calves. Our findings suggest that SCB would deserve more attention as a modulator of the gastrointestinal health in young dairy calves.