Longitudinal Change in Rumen-Associated Bacterial Communities Following Aso Limonite Supplementation in Japanese Brown Cattle

Aso limonite, a natural volcanic mineral, has been used as a cattle supplement in the Aso region of Japan; however, its effects have not been well-characterized. This study examined whether Aso limonite supplementation from 105 days prepartum to 90 days postpartum changed rumen-associated bacterial communities and calf growth in the Kumamoto strain of Japanese Brown cattle. Buccal swab-derived bacterial profiles were regarded as proxies of examining rumen-associated bacterial communities. Diversity analysis detected prepartum differences between the control and limonite groups. Primary longitudinal screening further identified rumen-associated, oral-associated and archaea subsets from buccal swab-derived microbiota. Within the rumen-associated subset, Blastomonas and Denitromonas emerged as representative taxa showing interaction-associated signals at day −45 in the limonite group, whereas Adlercreutzia showed different pattern at day −15 in the control group. Additionally, heatmap and network analyses showed that these taxa were found in distinct broader rumen-associated bacterial communities rather than a single common taxon. In parallel, calves born to limonite-fed dams were heavier than those from control dams between days 28 to 84 postpartum. These findings indicate that maternal limonite supplementation was associated with selective changes in rumen-associated bacterial communities together with greater early calf body weight.