Abstract
Calf diarrhea is a prevalent and significant health issue in dairy farming, severely impacting feed intake, weight gain, and survival rates in young calves. This study aimed to investigate the microbial composition and antibiotic resistance profiles of diarrheic calves to provide insights into the epidemiology and management of the condition. The prevalence of diarrhea in 1685 calves was analyzed. Rectal fecal samples were collected from five healthy and five diarrheic Holstein calves on a large dairy farm in Shaanxi Province, China. High-throughput 16S-rRNA sequencing and PCR were utilized for microbial and resistance gene analysis. In 2023, the overall diarrhea rate among 1685 calves was 9.08%, with a significantly higher diarrhea rate during the suckling period (8.13%) compared to the post-weaning period (0.95%) (p < 0.001). No differences in species diversity and richness were detected among the different groups. However, LEfSe analysis identified six genera (Eubacterium, Eubacteriaceae, Prevotella, Comamonadaceae, Comamonas, and Firmicutes) significantly enriched in diarrheic calves compared to healthy ones (LDA scores > 2, p < 0.05). Additionally, antibiotic resistance genes for quinolones, β-lactams, chloramphenicol, tetracyclines, and aminoglycosides were detected, with significantly higher prevalence in diarrheic calves. These findings demonstrate distinct microbial and antibiotic resistance profiles between healthy and diarrheic calves, emphasizing the importance of microbial management in controlling calf diarrhea.