Impact of probiotic supplementation on the growth, health, and fecal microbiota of Argentine Holstein calves

This study aimed to evaluate the impact of probiotic administration on the growth, health status, and fecal microbiota of Argentine Holstein calves. Thirty calves from a commercial dairy farm were assigned to two groups. The treated group received a daily oral capsule containing four Lactobacillus strains (1x10 ⁹ CFU), from 2 to 30 days of age, while the control group received a placebo capsule following the same schedule. After colostrum feeding, all animals were provided with a milk replacer and formulated compound feed. Health status was monitored using the Wisconsin test to assess diarrhea, and body weight was measured at 2 and 60 days of age. Fecal microbiota was evaluated at 30 ± 3 days using 16S rRNA gene sequencing targeting the V3-V4 regions. No significant differences were observed between groups in terms of diarrhea and weight gain. Similarly, 16S rRNA gene sequencing revealed no notable differences in bacterial community structure between groups. The most abundant family identified was Muribaculaceae; while dominant genera included Bacteroides , Prevotella , Collinsella , Alloprevotella , and Lactobacillus. The probiotic treatment proposed had no effect on diarrhea incidence or growth performance but caused no harmful effects either.