Glycerol combined with oils did not limit biohydrogenation of unsaturated fatty acid but reduced methane production in vitro

Three runs of in vitro incubations were conducted to evaluate the effect of glycerol (0 or 150 g/kg DM) combined with three different diets: Tifton 85 hay at 850 g/kg DM without oil seeds (HWO), Tifton 85 hay + 80 g of soybean oil/kg DM (HSO) and Tifton 85 hay + 80 g of linseed oil/kg DM (HLO) incubated for 0, 6, 12 and 24 h on fatty acid composition and ruminal fermentation parameters. Real-time PCR was used to quantify microbial population at 24 h. Methanogens, fibrolitic and lipolityc bacteria were expressed as a proportion of total rumen bacterial 16S rDNA. Separately, kinetic of gas production was assessed at 2, 4, 6, 8, 10, 12, 14, 18, 22, 24, 36, 42 and 48 h. In vitro true digestibility, g/kg (IVTD) and CH4 (%/g DMD) production were evaluated at 48 h. The experimental design for fatty acid composition and ruminal parameters was a randomized block in a factorial arrangement 2 × 3 × 4, glycerol, diets and time, respectively. Microbial quantification, IVTD and methane were evaluated with the same design but without time as a factor. The pH value and ammonia concentration were lower in HWO compared with HSO and HLO diets, independent of glycerol addition. Ruminococcus albus, Ruminococcus flavefaciens, Butyrivrio vaccenic acid and stearic acid subgroup did not change with glycerol and oil addition (P>0.05). Among all cellulolytic bacteria, Fibrobacter succinogenes was the most sensitive to the addition of vegetable oil in the diet. Methane production decreased in HSO diet combined with glycerol and HLO diets with or without glycerol addition. Lag time (h) from the gas production kinetics decreased in HWO and HSO diets combined with glycerol. The C2:C3 ratio decreased in diets with glycerol addition. Glycerol inclusion did not reduce biohydrogenation of unsaturated fatty acids in vitro. Glycerol was ineffective to reduce the potentially negative effects of vegetable oils on ruminal fermentation and digestibility in vitro. Indeed, the proportion of Anaerovibrio lipolytica increased in all diets with glycerol added and unsaturated fatty acids profile remained unchanged.