The effect of supplementing Nannochloropsis oculata microalgae on ruminal fermentation, methane production and microbial population

This study aimed to evaluate the dietary supplementation of Nannochloropsis oculata (N. oculata) microalgae in different levels (1-, 2-, 3-, 4-, and 5- g/100 g dry matter (DM)) on the kinetics of gas production (GP), methane (CH4) production, dry matter apparent digestibility, volatile fatty acids (VFA), and microbial population by in vitro method. The findings of this study indicated that adding N. oculata at levels of 1-5 g/100 g DM did not have an impact on GP at different incubation hours. However, a diet with 5 g/100 g DM N. oculata resulted in a consistent increase in GP rate (part c) compared to the control treatment (P < 0.0001). Supplementing of N . oculata to the diet decreased the CH4 production (P < 0.001), methane to gas production ratio in 24 h (P < 0.0001), protozoa population (P < 0.002), total VFA (P < 0.005), Fibrobacter succinogenes, Ruminococcus flavefaciens, Prevotella spp., Anaerovibrio lipolytica, and Butyrivibrio proteoclasticus, and increased the partitioning factor (P < 0.0001), pH (P < 0.001), Ruminococcus albus, Butyrivibrio fibrisolvens, B. fibrisolvens, S. ruminantium, and fungi population (P < 0.0001). The addition of N. oculata did not impact on the levels of dry matter digestibility, ammonia nitrogen, acetate, propionate, and butyrate. However, this study demonstrated that N. oculata effectively decreased methane production and the presence of methanogenic archaea by more than 3 g/100 g DM in the diet. Therefore, N. oculata can be considered as a beneficial biological supplement for reducing methane emissions in animal feed. Nevertheless, further experiments are required to determine the optimal supplementation level for practical application.