Abstract The study involved randomly assigning rumen fluid from 10 Polish Holstein-Friesian cows, fed a standard balanced diet, to a four-replicated treatment: i. control (CTRL): 25% alfalfa, 25% green grass, and 50% corn grain; ii. SR1: CTRL with soapwort root in a 1:1 ratio; iii. SR2: CTRL with soapwort root in a 1:3 ratio; and iv. powdered soapwort root. Four 24-hour in vitro fermentations were conducted, analysing 40 samples. After fermentation, total gas production, pH, methane (CH 4 ) concentration, volatile fatty acids (VFA) production and profiles, hydrogen recovery, and hydrogen consumption ratio were measured. The study indicated that the gas production rate starts to decrease after 8 hours for all treatments concerning CTRL. Furthermore, it revealed that soapwort root reduced CH 4 production in all experimental feeding models, metabolic hydrogen recovery, and the CH 4 to VFA ratio. In addition to this, we observed an increase in the propionic acid content in all groups supplemented with the soapwort root. The low values of the VFA utilisation index (NGR) and the acetic–propionic ratio, as well as the high values of the propionic– butyric ratio, indicate a reduced level of methanogenesis without loss of metabolic energy. In our opinion, the root is characterised by a high level of saponins, which slightly affects the nutritional value of the feed, making it a good additive for reducing CH 4 emissions.
Pecka-Kiełb et al. (Sun,) studied this question.