Rumen fermentation, methane concentration and fatty acid proportion in the rumen and milk of dairy cows fed condensed tannin and/or fish-soybean oils blend

Two experimental factors (extract from Vaccinium vitis idaea (VVI) and blend of fish-soybean oils) were investigated in three consecutive experiments to monitor their effects on rumen fermentation and fatty acid (FA) proportions in the rumen fluid and milk. Firstly, in vitro experiment was performed using a semicontinuous culture system (RUSITEC). Four treatments were included: (1) CON-control diet without experimental factors; (2) VVI-control diet with 4.5 g of VVI/kg of DM; (3) FSM-control diet with 30 g of fish and soybean oils blend/kg of DM; (4) MIX-control diet with 4.5 g of VVI/kg of DM and 30 g of oils blend/kg of DM. The proportions of C18:1 t10, C18:1 t11 and C18:1 c9 FA increased (P < 0.002) in FSM and MIX treatments. Abundance of Butyrivibrio fibrisolvens and Butyrivibrio proteoclasticus was significantly reduced in three treatments (VVI, FSM, MIX; P < 0.019). Moreover, the MIX significantly decreased methane concentrations by 21% in comparison with the CON (P < 0.002). Based on preliminary in vitro results from the first experiment, the second, in vivo experiment was conducted using four Polish Holstein-Friesian cows fitted with rumen cannulas. Cows received the diet as a partial mix ration in two variants: (1) CON diet without supplementation (2) MIX diet containing a mixture of VVI dried leaves extract as a source of condensed tannins (4.83 g/kg DM of total diet) and a blend of fish-soybean oils as a source of unsaturated FA (32.2 g/kg) DM of total diet. For the MIX treatment, the proportions of C18:2 c9-c12, C18:2 c9-t11 and C18:2 t10-c12 in the rumen fluid were affected (P < 0.05), whereas the DNA concentration for B. fibrisolvens and B. proteoclasticus was not changed. Thus the MIX treatment exerted an antimicrobial activity by decreasing protozoa and methanogen numbers, thereby reducing rumen methane production. Finally, the third, production experiment was conducted on 12 lactating Polish Holstein-Friesian cows subjected to the same treatment as the cannulated cows in the second experiment. The MIX treatment did not modify the proportions of majority of the unsaturated FA in milk. The MIX treatment also did not change expression of the six investigated genes: acetyl-CoA carboxylase 1 (ACACA), fatty acid synthase (FASN), lipoprotein lipase (LPL), stearoyl-CoAdesaturase (SCD), fatty acid desaturase 1 (FADS1), fatty acid elongase 5 (ELOVL5). In conclusion, unexpectedly, the MIX treatment did not change the milk FA proportion, and this phenomenon could be attributed to a lack of effects of the both provided supplements. In spite of that, the MIX treatment significantly decreased the methanogenesis.