Comparison of alfalfa, birdsfoot trefoil, and cicer milkvetch in combination with 25, 50, or 75% tall fescue in a continuous-culture system1

A continuous-culture experiment was performed to investigate the effects of tall fescue (TF)-to-legume ratios (TF:legume = 75:25, 50:50, or 25:75 on a DM basis) of 3 different TF-legume mixed diets [TF-alfalfa (TF+AF), TF-birdsfoot trefoil (TF+BT), or TF-cicer milkvetch (TF+CM)] on in vitro fermentation characteristics. Nine dietary treatments were tested in a 3 (TF-legume ratio) × 3 (TF-legume mixed diet) split-plot design. Dietary treatments did not affect the concentrations of total VFA, acetate, and butyrate, whereas increasing legume proportion increased propionate concentration (P = 0.03). Regardless of TF-legume ratio, feeding TF+CM re sulted in the greatest propionate concentration, whereas TF+AF and TF+BT maintained a similar concentration of propionate. The TF+AF combination resulted in a greater acetate-to-propionate ratio than TF+BT or TF+CM (P = 0.03). Decrease in ammonia-N concentration (P < 0.01) was noticed when legume proportion decreased. Ammonia-N concentration of TF+CM decreased (P < 0.01) compared with TF+AF, and it further decreased in cultures receiving TF+BT (P < 0.01). Methane production was decreased by increasing legume proportions, and the result was particularly notable in TF+BT due to increased condensed tannin concentration. In addition, TF+BT increased the proportion of C18:1 trans-11 and decreased C18:0 in the culture (P < 0.01), but no effects were detected because of legume ratio. Results of this experiment indicate that increasing the proportion of legume in combination with TF favorably shifted in vitro fermentation pathways by producing more propionate and less ammonia-N and methane.