Humic acid supplementation modulates ruminal and fecal microbial communities in lamb

The gastrointestinal microbiome affects the health and productivity of animals. Modifying these traits with additives may enhance their effects, making it a relevant strategy. This study investigated the effects of humic acids (HA) on the ruminal and fecal microbiomes of lambs and its potential adherence to ruminal mucosa. Twenty weaned Hampshire Down crossbred lambs aged 102.1 ± 6.6 days with an average body weight of 24.2 ± 3.5 kg were randomly allocated into two groups. Control group was fed a basal diet without HA, and treatment group was fed a basal diet with commercial HA at a dose of 500 mg/kg BW/day for 56 days. At the end of the experiment, ruminal and fecal samples were analyzed using 16S rRNA gene sequencing, and ruminal mucosal tissue from the slaughtered lambs was evaluated using histology and scanning electron microscopy (SEM). The addition of HA to the feed of lambs increased the relative abundance of the genus Bifidobacterium and decreased the genus Lachnospiraceae CAG-127 in the ruminal microbiome of lambs. Furthermore, an increase in the relative abundance of the genera Acutalibacteraceae UBA5905 and Lachnospiraceae VUNI01, along with a reduction in the order Campylobacterales and the genus Acutalibacteraceae CAG-180 was observed in the fecal microbiome. HA was not found in the ruminal mucosa of lambs, as determined by histology or SEM. HA supplementation modulated the ruminal and fecal microbiomes of lambs by reducing harmful and increasing beneficial bacteria, highlighting its potential as a functional feed additive to support ovine gut health.