Rumen fermentation and microbial profiles of sheep fed a high-concentrate diet supplemented with ellagic acid

The purpose of this study was to observe the effects of ellagic acid on rumen fermentation and microbial diversity in sheep fed a high-concentrate diet (with a concentrate-to-forage ratio of 65 ꞉ 35) to provide a reference for its application in ruminant production. Five healthy, non-pregnant, small-tailed Han ewes with an average body weight of approximately 40 kg, equipped with a permanent rumen fistula were selected as experimental animals. A self-controlled design was used and the experiment was divided into two phases, the control and experimental phases. In the control phase, sheep were fed a basal diet. In the experimental phase, ellagic acid was administered at a dose of 10 g·(d·sheep)⁻¹ in addition to the basal diet. During each of the phases, 12 days were designated for adaptation, followed by 3 days for the collection of rumen contents. This was then used to determine ruminal fermentation parameters. The diversity and relative abundance of rumen bacteria, methanogenic archaea, and fungi were analyzed using 16S rDNA sequencing. The results showed that the addition of ellagic acid had no significant effect on feed intake, ruminal pH, predicted CH₄ production, the contents of NH₃-N and microbial protein, or protozoan number (P > 0.05). The total volatile fatty acids showed a significant decrease (P < 0.05); however, the molar ratio of acetate to isobutyrate was not significantly affected (P > 0.05). The proportion of propionate and isovalerate decreased significantly, whereas the butyrate, valerate, and acetate to propionate ratios increased significantly (P < 0.05). High-throughput sequencing showed that ellagic acid had no significant effect on the diversity of ruminal bacteria, fungi, and methanogens (P > 0.05). However, the relative abundances of Dialister, Ruminococcus 2, Syntrophococcus, and Solobacterium genera of ruminal bacteria increased (P < 0.05), whereas the relative abundances of Saccharofermentans and Ruminococcus 1 decreased (P < 0.05). In conclusion, ellagic acid mainly acts on ruminal Firmicutes, changes rumen bacterial communities and the proportion of short-chain fatty acids, and reduces the production of total volatile fatty acids.