PSII-18 - Effect of Alfalfa and Meadow Bromegrass Monocultures and Binary Mixtures with Sainfoin on In Vitro Ruminal Fermentation Using the Rumen Simulation Technique (RUSITEC)

Abstract: An in vitro rumen stimulation (RUSITEC) study was conducted to determine the effect of alfalfa and meadow bromegrass monocultures and binary mixtures with sainfoin on nutrient disappearance, ruminal fermentation, total gas and methane production, and microbial protein synthesis. Treatments were assigned (4 vessels/treatment) to two RUSITECs in a randomized complete block design. Treatments included (DM basis): 1) 100% alfalfa (22% bloom; ALF), 2) 100% Armada meadow bromegrass (R2 stage, spikelet fully emerged; MBR), 3) 70% alfalfa + 30% sainfoin (40% bloom; ALF+SAN), and 4) 70% Armada meadow bromegrass + 30% sainfoin (MBR+SAN). The experiment consisted of 7 d of adaptation and 7 d of sampling. Data were analyzed in SAS using PROC mixed including fixed effects of forage treatments. Random effects included RUSITEC apparatus and cow rumen inoculum (n = 4). Contrast were included to compare ALF vs. MBR treatments and the effect of SAN inclusion (monoculture vs. binary mixtures). Dry matter and organic matter disappearance were greater (P < 0.01) for ALF treatments than MBR but were not affected (P ≥ 0.06) by SAN inclusion. Neutral detergent fibre, acid detergent fibre, and true crude protein disappearance were greater (P < 0.01) for MBR treatments than ALF and they decreased (P < 0.01) with SAN inclusion. Total volatile fatty acid (VFA) production was not affected (P = 0.54) by treatments. However, MBR treatments promoted greater (P ≤ 0.01) molar proportions of acetate and propionate than ALF, but SAN inclusion did not affect the response (P ≥ 0.28). Branched-chain VFA molar proportion were greater (P < 0.01) for ALF treatments compared to MBR. Consequently, acetate:propionate was reduced (P = 0.02) with MBR treatments compared with ALF and not affected (P = 0.70) by SAN. Methane production (mg/d, mg/g of DM incubated, or mg/g DM digested) was less (P ≤ 0.03) for ALF treatments compared to MBR and increased (P ≤ 0.01) with SAN inclusion. Total microbial N production was greater (P = 0.02) for ALF treatments compared to MBR but was not affected (P = 0.21) by SAN inclusion. In conclusion, the addition of SAN in binary mixtures decreased ruminal fermentation and increased methane produced by the fermenters. The ALF treatment promoted greater microbial N production and lower methane production.