Differences in Digestive Kinetics and Methane Production Among Rhizoma Peanut (Arachis glabrata Benth) Cultivars

Our objective was to determine if fermentation dynamics of 8 rhizoma peanut (RP; Arachis glabrata Benth.) cultivars differed among themselves and alfalfa (Medicago sativa L.). Rhizoma peanut is a hardy sub-tropical legume of comparable nutritive value to alfalfa, but produces polyphenol-oxidase (PPO), which may potentially result in a protein sparing due to antimicrobial properties. Although alfalfa and RP demonstrate similar nutritive profiles, prior research indicates decreased ruminal protein degradation rates of RP may improve N use efficiency relative to non-PPO producing forages. Polyphenol-oxidase enzymes from RP and red clover (Trifolium pretense L.) decrease proteolysis during ensiling and within the rumen, decrease plant-facilitated lipolysis, reduce polyunsaturated fatty acid biohydrogenation, and lower methane (CH₄) emissions. There is a large variation in nutritive value and PPO production among RP cultivars, signifying the need to screen. In our preliminary analysis, RP cultivars Arblick, Florigraze, UF Peace, Latitude 34, Arbrook, Ecoturf, UF Tito, and variety not specified (VNS) were hand collected late in the 2016 growing season from the Texas A&M AgriLife Research Center at Beeville, TX. Via in vitro gas production technique (IVGP), we determined 48 h fermentation dynamics of each RP cultivar and alfalfa. Measurements of CH₄ via gas chromatography, pH and redox potential, and digested residue were analyzed. Kinetic analysis of cumulative 48 h gas production was performed using GasFit. All cultivar kinetics fit the exponential model with discrete lag times. There were no differences (P > 0.05) among RP cultivars for total gas production, fermentation rate, lag time, total CH₄ g/L, or CH₄ ­g/L per g of NDF digested. There were no differences between PP cultivars and alfalfa for total gas production, lag time, or total CH₄ (g/L). However, fractional rate of fermentation was slower for alfalfa vs. UF Peace (9.44 vs. 19.76 %/h, P =0.03), but were not different from other cultivars (12.94, 17.62, 17.79, 14.62, 11.69, 17.89, 16.53 %/h, respectively for Arblick, Florigraze, Latitude 34, Arbrook, Ecoturf, VNS, and UF Tito) and marginal mean differences could not be determined using Tukey’s HSD. Further analyses of neutral detergent insoluble N and PPO are required to determine the impact of PPO on N metabolism. Based on these in vitro findings RP may serve as a viable forage substitute, nutritionally and environmentally.