Effects of the Inclusion of Linseed and Increasing Concentrations of Glycerol As Replacement of Corn Grain on Rumen Fermentation, Methane Production and Nutrient Disappearance in a Rusitec System

The aim of the study was to assess the effects of using linseed and increasing concentrations of glycerol in a forage diet supplemented with corn grain on nutrient disappearance, methane (CH₄) production and fermentation parameters in a Rusitec fermentation system. The experimental diets were: control, (70% ryegrass/clover mixed hay, 30% corn grain); positive control (70% hay, 15% corn grain, 15% linseed); 5% glycerol (70% hay, 10% corn grain, 15% linseed, 5% glycerol); 10% glycerol (70% hay, 5% corn grain, 15% linseed, 10% glycerol). The experiment was a complete randomized design with the four dietary treatments with 2 replicates in an 8 fermenter Rusitec apparatus. Incubations were run twice during 15d. The first 10d were used for fermenter adaptation, followed by 5d of sampling (days 11 to 15). The individual fermenter was the experimental unit. The model included the fixed effects of diet, day and diet/day interactions with the day of sampling from each fermenter treated as a repeated measure. Total VFA concentrations in effluent were increased (P = 0.005) in the glycerol added diets as compared to positive control. Acetate concentrations were reduced with increasing glycerol concentration in diets whereas propionate increased with linseed inclusion. Increasing concentrations of glycerol resulted in further increased propionate concentrations (P < 0.001), thus leading to important reductions in the acetate/propionate ratio. However, CH₄ production (mgCH₄/g DM digested) was reduced by linseed inclusion in the diet (P = 0.004) but not by increasing concentrations of glycerol in the diet. Ammonia nitrogen was increased in all linseed supplemented diets (P < 0.001). Total DM and non-fibrous carbohydrates in vitro disappearance were not affected by dietary treatments (P = 0.411). However, CP and EE disappearance were increased in linseed supplemented diets (P < 0.001) but not further affected by glycerol inclusion. Disappearance of NDF was increased only in the positive control diet as compared to control diet (P = 0.0185). In conclusion, the use of linseed as replacement of corn grain reduces CH₄ production in a Rusitec system but increases ammonia nitrogen. Increased propionate concentrations in glycerol supplemented fermenters does not result in reduced CH₄ production despite increases in propionate concentrations. Linseed inclusion increases in vitro disappearance of CP and EE without affecting total DM disappearance.