Effects of different Ascophyllum nodosum and Sargassum fusiforme levels on in vitro rumen fermentation parameters of a high-concentrate level diet in Hu sheep

In this study, we investigated the effects of adding Ascophyllum nodosum and Sargassum fusiforme on the in vitro fermentation parameters in Hu sheep of a high-concentrate diet and sought to clarify their optimal proportions capable of relieving rumen acidosis. We used in vitro batch culture to study five supplemental levels (0% as control, 1%, 2%, 3%, and 4%, dry matter basis) of Ascophyllum nodosum (ASC₀, ASC₁, ASC₂, ASC₃, and ASC₄, respectively) and Sargassum fusiforme (SAR₀, SAR₁, SAR₂, SAR₃, and SAR₄, respectively) when the concentration-to-forage ratio was 70꞉30. The pH, ammonia nitrogen (NH₃-N), microbial protein (MCP), lactic acid, and volatile fatty acid contents of the fermentation broth under different treatment conditions were determined at 6, 9, 12 and 24 h. The pH of the fermentation broth of the ASC₃, ASC4, and SAR₃ groups was significantly higher (P < 0.05) than that of the respective control groups at each time point of fermentation. The concentration of NH ₃-N in the ASC₃ and SAR₃ groups at 12 and 24 h of fermentation was significantly decreased (P < 0.05) compared with that in ASC0 and SAR0 groups. The concentration of MCP in the ASC ₃ and SAR₃ groups at 24 h was significantly higher (P < 0.05) than that in the ASC ₀ and SAR₀ groups. The concentration of lactic acid in the fermentation broth of Ascophyllum nodosum and Sargassum fusiforme supplementation groups was significantly lower (P < 0.05) than that in the control groups at 24 h of fermentation. The acetate-to-propionate ratio of each supplementation group was significantly increased ( P < 0.05) compared with that of the ASC ₀ group, whereas the proportion of propionate was significantly decreased (P < 0.05) at each time point of fermentation. Compared with that in the SAR ₀ group, the proportion of acetate and acetate-to-propionate ratio in the SAR₃ group were significantly increased (P < 0.05), whereas the proportion of propionate was significantly decreased ( P < 0.05) at 24 h of fermentation. In conclusion, the addition of A. nodosum or S. fusiforme can effectively alleviate the pH decrease, reduce lactic acid concentration, increase the acetate-to-propionate ratio, and improve the rumen fermentation pattern. These effects have the potential to alleviate rumen acidosis. Under the conditions of this experiment, the optimal concentrations of A. nodosum and S. fusiforme to relieve ruminal acidosis were 3%.