151. Effects of Dried Seaweed, Micro-fused Essential Oil, and Lactobacillus Reuteri on Rumenmicrobiota and Performance of Sheep.

Abstract This study evaluated the effects of dried seaweed meal (DSM), micro-fused essential oil (MEO), and Lactobacillus reuteri (LR) on rumen microbiota and growth performance of crossbred sheep in a 35-d feeding trial. Thirty-six Katahdin sheep (BW = 21.11 ± 0.20 kg) were randomly assigned (n = 9/group) to: control basal diet (CON), CON + 5 g/head/d DSM (Ascophyllum nodosum), CON + 4 g/head/d MEO (Thyme white, cinnamon and oregano), or CON + 10 g/head/d LR (2 × 109 CFU/g)). Dry matter intake (DMI) and average daily gain (ADG) were measured. Supplemented groups tended to have higher ADG (p-value = 0.06) than CON despite similar DMI. DNA extract from rumen fluid collected on d-35 was used for sequencing. Metagenomic analysis revealed differential abundance of key taxa across treatments. Prevotella, Lachnospiraceae, Clostridium, and Treponema were differentially abundant. DSM increased hydrogenotrophic Duodenibacilluswhile reducing methanogenic archaea including Methanobrevibacter ruminantium, M. smithii, and M. stadtmanae. MEO suppressed cellulolytic Fibrobacter succinogenes and Ruminococcus spp. while enriching Butyrivibrio and Anaerovibrio associated with biohydrogenation of unsaturated fatty acids. LR enhanced Megasphaera and Selenomonas, and lactate-utilizing bacteria Methanomicrobiaceae and Methanosphaera were differentially reduced across all additive groups. These findings indicate that DSM, MEO, and LR each shift the rumen microbiota toward propionate-favoring, methanogen-suppressing communities through distinct mechanisms, with potential to improve feed efficiency and reduce greenhouse gas emissions in sheep production.