Effects of replacing barley grain in feedlot diets with increasing levels of glycerol on in vitro fermentation and methane production

The aim of the study was to assess impacts of increasing dietary levels of glycerol on in vitro ruminal fermentation and CH4 production from a barley based feedlot diet. Glycerol was used as replacement for barley grain at inclusions of 0, 70, 140 and 210 g/kg of diet dry matter (DM) in a diet containing an equal mixture of barley grain and barley silage. Both grain and silage were dried and ground through a 1 mm screen before mixing with glycerol. The experiment was repeated (n = 2) using ANKOM® bags in 50 ml sealed batch culture serum vials (i.e., 0.5 g substrate + 25 ml media) with a 3:1 ratio of buffer:rumen liquor (n = 5 bags/treatment/experiment). Rumen liquor was obtained from two cows fed a diet containing 710 g/kg barley silage, 250 g/kg barley grain and 40 g/kg concentrate (DM basis). Gas production was measured by water displacement at 3, 6, 12, 24, 36 and 48 h after inoculation. Volumes corrected for gas released from 15 negative controls (i.e., no substrate) were used to estimate net gas production at 24 and 48 h. Gas samples collected at 24 and 48 h were analyzed for CH4 concentration. In vitro DM disappearance (IVDMD) and culture pH were measured at 48 h. Cumulative gas production as ml/g DM substrate and IVDMD were similar among treatments. Culture pH did not differ among treatments. Total CH4 production (as mg or as mg CH4/g digested DM) did not differ among treatments. Results suggest that replacing barley grain with glycerol did not reduce in vitro CH4 production as a function of digested DM or substrate DM. rticle is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.