PS10-7. Ruminal Fermentation in vitro Screening of Perennial Forages for Improved Nutrient Disappearance and Lower Methane Production.

Abstract Ruminal in vitro batch culture trials are useful tools for ranking forage varieties before undertaking labor-intensive and costly grazing studies with beef cattle. This study screened new perennial forage varieties and binary mixtures, including alfalfa, for improved digestibility, ruminal fermentation profile, and low methane (CH4) production using the ruminal in vitro gas production technique. From 2023 to 2025, a 3-year forage plot trial was conducted at Clavet, SK, Canada. Each treatment was replicated (n = 4) in 2.4 × 6 m plots. The 11 treatments evaluated were: 1) alfalfa (ALF, Medicago sativa L.) variety Equinox, 2) ALF S914 (new variety), 3) meadow bromegrass (MBG, Bromus riparius Rehm.) var. CDC Torsion, 4) Hybrid bromegrass (HBG, Bromus riparius × B. inermis) var. AAC Torque, 5) hybrid wheatgrass (WTG, Triticum aestivum L.) var. CDC Saltking, 6) ALF Equinox + Torsion, 7) ALF Equinox + Torque, 8) ALF Equinox + Saltking, 9) ALF S914 + Torsion, 10) ALF S914 + Torque, and 11) ALF S914 + Saltking. Treatments were arranged in a randomized complete block design and replicated over two in vitro runs. Gas pressure in each vial was measured at 6, 12, 24, and 48 h of incubation. At the same time, 20 mL of gas was sampled for CH4 analysis. The dry matter (DMD), neutral (NDFD), and acid detergent fiber (ADFD) disappearance were determined after 48 h of incubation. Data were analyzed using the nlme package in R, with forage treatment and year (1-3) as fixed effects, and field plot (1–4) and experimental run (1–2) as random effects. Time was included in the model as a fixed effect and as a repeated-measures factor for the gas and methane data analysis. Treatment means were compared using orthogonal contrasts and were declared significant at P ≤ 0.05. Legume monocultures or legume–grass binary mixtures did not differ (P > 0.05) for CH4 production (mL/g DMD). However, MBG Torsion produced 13.6% lower CH4 than WTG Saltking (121.5 vs. 138.0 mL/g DMD; P < 0.01). ALF S914 showed greater DMD than ALF Equinox in both 2023 (71.2 vs. 68.4%; P = 0.01) and 2025 (62.9 vs. 60.0%; P < 0.01). In 2023, WTG Saltking had lower DMD than MBG Torsion (54.5 vs. 60.2%; P < 0.01) and HBG Torque (54.5 vs. 58.7%; P < 0.01). Similarly, WTG Saltking exhibited lower NDFD (37.8 vs. 43.3%; P < 0.01) and ADFD (34.2 vs. 38.9%; P < 0.01) compared with MBG Torsion. Overall, MBG Torsion, HBG Torque, and ALF S914 demonstrated superior in vitro ruminal fermentation and appear to be promising candidates for further evaluation in grazing studies, either as monocultures or in legume–grass binary mixtures.