In vitro gas production and ruminal fermentation of glycerol, propylene glycol and molasses

Ruminal fermentation pattern and in vitro gas production was determined for three energy sources for ruminants, glycerol, propylene glycol and molasses with ruminal fluid from sheep. Substrates incubated were alfalfa, corn silage, glycerol (320 and 640 μl), propylene glycol (320 and 640 μl) and molasses (320 μl). The greater volume of gas produced was observed at the highest dose of glycerol which also showed the slowest rate of gas production and the longest lag time (P<0.05). Propylene glycol presented the minor volume of gas and was rapidly metabolized with short lag time. Molasses presented typical characteristics of a rapidly available substrate, with the fastest rate of gas production (P<0.05). Glycerol fermentation resulted in a reduction of acetate, a slight increase in propionate and an increment in percentage of butyrate. Incubations with propylene glycol also reduced acetate and butyrate, but increased propionate (P<0.05). Molasses fermentation reduced acetate and increased propionate and butyrate. Increasing dose of energy sources resulting in a greater volume of gas produced. In conclusion, glycerol fermentation reduced acetate and increased the molar proportion of butyrate and propionate was the main product of fermentation of propylene glycol.