Impact of forage mixtures on rumen energetics and performance as assessed by continuous culture

Grass-fed organic systems are becoming more prevalent in the Northeast, and these grass-fed systems rely on pastures during the grazing season as the main diet component. While pastures in the Northeast are typically species-diverse, research characterizing the impacts of diversification is lacking. The objective of this study was to evaluate rumen energetics and performance using an in vitro continuous culture fermenter system receiving diverse forage mixtures. Treatments were assigned at random to fermenters in a 4 x 4 Latin square design. Within each 10-d period, fermenters were allowed to adapt for 7 d followed by a 3 d of sampling. Dietary treatments on a dry matter (DM) basis included 1) 50% orchardgrass + 50% alfalfa (OG-ALF); 2) 50% OG-ALF + 50% red clover (RC); 3) 50% OG-ALF + 50% pearl millet (MIL); and 4) 50% OG-ALF + 50% sorghum x sudangrass (SUD). To imitate grazing patterns of typical intensive grazing systems, forage diets (131 g DM/ fermenter/ d) were divided into 4 portions per day (33% of DM at 0600 h; 17% of DM at 0720 h; 33% of DM at 1800 h; 17% of DM 1920 h). Fermenter pH measurements were collected every min for the entirety of the experiment. Methane (CH4) concentration of the gas headspace was measured using a gas analyzer probe and recorded twice daily (0530 and 1730 h) in triplicate on d 7, 8, 9, and 10. For volatile fatty acid (VFA) analysis, 24 h effluent samples were composited and collected on d 8, 9, and 10. Results were analyzed using PROC MIXED of SAS 9.4. Fermenter pH did not differ between fermenters as a result of treatment (P \u3e 0.05) nor did total VFA concentrations (P = 0.08), VFA molar proportions (P \u3e 0.05), or individual VFA ratios (P \u3e 0.05). However, fermenters receiving OG-ALF had the greatest CH4 concentration (50.8 mg/dL). This was significantly higher (P \u3c 0.05) than the CH4 concentrations in fermenters receiving MIL (6.2 mg/dL), SUD (6.9 mg/dL), or RC (21.2 mg/dL) treatments. Gas CH4 concentrations from fermenters receiving MIL, SUD or RC did not differ (P \u3e 0.05) from each other. These results suggest that diversifying forage profiles by including warm-season annuals with cool-season perennials could potentially provide benefits to dairy cattle by altering energetic capture. Additionally, inclusion of warm-season annuals may potentially improve rumen energetic capture through mitigation of CH4 production