Changes in the In Vitro Ruminal Fermentation of Diets for Dairy Cows Based on Selected Sorghum Cultivars Compared to Maize, Rye and Grass Silage

An in vitro experiment was conducted to determine the impact of silage produced from selected varieties of sorghum on the microbial fermentation profile of cows’ ruminal fluid. To determine the main microbial fermentation products, ruminal fluid samples were obtained from Polish Holstein–Friesian cows. Serum bottles were filled with 80 mL of ruminal samples, and 1 g of one of the following substrates was added: corn silage (CS), grass silage (GS), rye silage (RS), sorghum silage (sweet) (SS1), sorghum silage (grain) (SS2) or sorghum silage (dual-purpose) (SS3). The serum bottles were flushed with CO2 and fermented for 8 and 24 h at 39 °C. After incubation, the obtained gas and rumen fluid were then analysed to determine the methane and volatile fatty acid (VFA) contents using gas chromatography. The use of sorghum silage (SS) resulted in a decrease in the total concentration VFA concentration in the ruminal fluid compared with the use of other silages, especially GS. Moreover, the ruminal fluid contained a lower molar proportion of propionic and butyric acids when SS was used compared with CS. The butyric acid proportion was higher in SS samples than in RS samples. The differences in chemical composition between sorghum varieties did not influence the rumen VFA concentration or profile. A decrease in gas production, but without effects on methanogenesis, was observed when SS was used compared with GS and CS. The analysis demonstrates the physiological processes of fermentation in the rumen, as evidenced by the products of microbial fermentation. The main advantage is that the addition of SS, irrespective of the plant variety, reduced fermentation gas production in the ruminal fluid compared with CS. The silage of the analyzed sorghum varieties may be used in the diets of dairy cows as a substitute for corn and grass silages.