Impact of adding tannins or medium-chain fatty acids in a dairy cow diet on variables of in vitro fermentation using a rumen simulation technique (RUSITEC) system

Abstract

This work aimed to evaluate the effect of including 2 functional feed ingredients in a diet with a high proportion of pasture silage on in vitro ruminal fermentation, nutrient disappearances, and ruminal microbiomes. In a rumen simulation technique (RUSITEC) system (6 fermentation units), 4 treatments were evaluated: 1) CONTROL: a diet based on corn and grass silage, regular soybean meal (SBM), and corn; 178 g/kg of crude protein (CP) (used as negative control), 2) TSBM: Replacement of SBM by Mervobest® (used as positive control), 3) PHY (phytogenic mixture (tannins from quebracho and chestnut) at 10 g/kg dry matter (DM) replacing SBM) and 4) MCFA (mixture of medium-chain fatty acids, Aromabiotic Cattle® at 10 g/kg DM replacing SBM). Four runs were performed with 3 diets incubated simultaneously in duplicate using a balanced incomplete block design, lasting 17 days each. The inoculum was obtained from 3 rumen fistulated cows, and artificial saliva was infused at 650 mL/day. Samples were taken from each fermentation unit to determine the gas production, pH, NH3-N, and volatile fatty acids concentrations. The apparent digestibility of diet compounds was determined. Microbial protein synthesis and microbial community diversity were estimated using 15N as an external isotopic marker and by sequencing part of the 16 S rDNA gene, respectively. The TSBM and PHY treatments decreased NH3-N concentrations (P < 0.001) and the DM disappearance (P = 0.004). The crude protein disappearance was the lowest for TSBM followed by PHY (P < 0.001). The true protein disappearance was lower for TSBM and PHY than for CONTROL and MCFA (P < 0.001). The isovaleric acid proportion was lower for TSBM, MCFA, and PHY than for CONTROL. Treatments TSBM and MCFA registered lower neutral detergent fibre disappearance (P < 0.001) than the other diets but without changes in the quantified fibrolytic genera in the ruminal microbiota. The PHY treatment increased the relative abundance of Succinivibrio spp. and reduced that of Methanobrevibacter relative to that of CONTROL and TSBM, which could be linked to lower methanogenesis. The MCFA treatment increased Succinivibrio compared with TSBM and Succiniclasticum spp. compared with CONTROL. These results indicate that PHY inclusion at 10 g/kg DM decreased rumen protein degradation, similar to TSBM; while MCFA decreased rumen protein degradation to a lesser extent. Furthermore, both additives generated changes in the ruminal microbiota that would be associated with lower methane production.