Effects of increasing n3:n6 ratio by replacing extruded soybeans with extruded flaxseed on dry matter intake, rumen fluid bacteria, and liver lipid metabolism in transition cows

Background The drop of dry matter intake (DMI) and rise of milk production in transitional dairy cows would mobilize reserved fat and disrupt lipid metabolism, eventually attributed to negative energy balance (NEB) and immune injury. The positive effect of n-3 polyunsaturated fatty acids (PUFA) on regulating energy metabolism and inflammation has been elucidated, however, the lack of regulatory mechanism of dairy cows deserves further investigation. In this study, 30 Holstein transition cows were divided into the control (CON) and HN3 groups based on the n-3: n-6 PUFA ratio in the diet. Results The results showed that compared to the CON group, high n-3: n-6 PUFA ratio-supplemented cows in the prepartum phase reduced the relative abundance of gram-negative bacteria in the rumen, the concentration of lipopolysaccharide in the plasma and liver also significantly decreased (P < 0.05). Transcriptomic analysis of the liver showed that the NF-κB signaling pathway significantly down-regulated and the taste transduction pathway up-regulated (P < 0.05) in the HN3 group. In the postpartum phase, a high n-3/n-6 PUFA ratio in the diet increased the relative abundance of Prevotella, Succinimonas and Treponema in the rumen, at the same time, orexins in plasma were also changed (P < 0.05). Further, the insulin resistance pathway significantly down-regulated and the taste transduction pathway up-regulated (P < 0.05) in the liver. Conclusions Overall, these results showed that a high n-3: n-6 PUFA ratio in the diet attenuates inflammatory responses in the prepartum phase and increases milk protein in the postpartum phase of transitional dairy cows. Appropriate increase in the proportion of n-3: n-6 PUFA ratio in the diet may be an effective measure to alleviate postpartum metabolic disease in dairy cows.