Humic acids reshape ruminal and fecal microbial communities in lambs

The gastrointestinal microbiome influences animal health and productivity, and its manipulation through additives may improve these traits. This study evaluated the effects of humic acid (HA) on the ruminal and fecal microbiomes of lambs and investigated whether HA adheres to the ruminal mucosa. Twenty weaned Hampshire Down crossbred lambs (102.1 +/- 6.6 days old; 24.2 +/- 3.5 kg) were assigned to two groups: a control group (basal diet) and a treatment group (basal diet + 500 mg HA/kg body weight/day for 56 days). At the end of the trial, ruminal and fecal samples were analyzed using 16S rRNA gene sequencing, and ruminal mucosa tissue was examined via histology and scanning electron microscopy. In the rumen, HA increased the relative abundance of the genus Bifidobacterium and reduced the genus Lachnospiraceae CAG-127. In feces, HA increased the genus Acutalibacteraceae UBA5905 and genus Lachnospiraceae VUNI01, while reducing the order Campylobacterales and the genus Acutalibacteraceae CAG-180. HA were not found in the ruminal mucosa of lambs by histological or scanning electron microscopy analyses. HA supplementation modulated the ruminal and fecal microbiome of lambs, reducing harmful and increasing beneficial bacteria.