In vitro investigation into the nutritive value of Lolium perenne bred for an elevated concentration of water-soluble carbohydrate and the added effect of sample processing: freeze-dried and ground vs. frozen and thawed

A novel Lolium perenne variety bred for an elevated concentration of water-soluble carbohydrate (WSC) Ba11353 ( high WSC; HWSC), which when grazed exhibited higher liveweight gains in lambs compared with a control ( AberElan), was analysed in vitro to determine its relative nutritive value. The effect of sample preparation was also investigated: frozen and thawed ( FT) vs. freeze-dried and ground (FDG). The nutritive value of the grasses was determined by in vitro measurements of gas production, which allowed assessment of both the rate and extent of fermentation of the grasses. Five FT and FDG samples of the two grasses (HWSC and control; n = 20) were suspended in an anaerobic medium, inoculated with rumen digesta and incubated at 39 degreesC for 120 h, with readings of gas pressure and volume made at regular intervals. At the end of the experimental period samples of liquid phase were taken to determine ammonia nitrogen and volatile fatty acid (VFA) concentrations. The WSC concentration of the HWSC was greater than the control (P = 0.03) whereas fibre concentrations were higher in the control (P = 0.002 and P = 0.01 for acid and neutral detergent fibres, respectively). The gas produced from the HWSC forages (both FT and FDG) had lower half-lives (the time at which half the total gas pool was produced), lag-times (P <0.001) and a greater predicted asymptote gas yield (P = 0.003) when compared to the corresponding control forage. For both grass varieties, the FDG treatment significantly reduced gas production half-life and lag-time and increased the gas yield and degradability compared to the FT treatment. Liquid phase ammonia-N concentrations were lower with HWSC (P = 0.04) compared to control. The FDG treatment of the grass led to a further reduction in ammonia-N concentration compared to the FT samples (P <0.001). Total VFA production was greater (P <0.001) for both HWSC treatments compared to the control, but no significant differences were noted between FT and FDG treatments. The glucogenic/lipogenic acid ratios (propionate/(acetate + butyrate)) were greater with HWSC (P <0.001). The FDG treatment further increased this ratio compared to the FT treatment (P = 0.002). This study helped to determine the nutritive value of high WSC grass through an evaluation of its fermentation properties when incubated in vitro with inoculated anaerobic media; it also provided evidence of how preparation of the samples can influence the results.