Effects of energy supplementation in pasture forages on in vitro ruminal fermentation characteristics in continuous cultures1

A dual-flow, continuous-culture system was used to assess the effects of energy supplementation with 4 pasture forages on in vitro ruminal fermentation characteristics. Twelve dietary treatments were tested in a split-plot design: energy supplementation (no concentrate, 30% ground corn, or 30% dried distilled grains with solubles) as a whole plot and pasture forages [tall fescue (TF) without N fertilizer, TF with N fertilizer (TF+NF), TF-alfalfa mixture, and TF-birdsfoot trefoil mixture (TF+BFT)] as a subplot. Three replicated runs lasted 9 d each, with 7 d for adaptation period and 2 d for data collection. The greatest total VFA and propionate concentrations (P < 0.01) were detected when corn was supplemented. Supplementing corn in the TF+BFT increased total VFA and propionate concentration (P < 0.05). Greater concentrations of acetate and propionate were found in the TF+NF (P < 0.01), but no effects were detected among other pasture forages. Energy supplementation decreased acetate:propionate ratio across pasture forages, and corn supplementation in the TF+NF resulted in the lowest ratio (P < 0.01). Lower ammonia-N and methane concentrations (P < 0.01) were achieved due to energy supplementation, in particular when corn grain was supplemented. Feeding the TF+NF or the TF+BFT elicited similar ammonia-N:VFA ratios with no energy or corn supplementation, which indicates that the TF+BFT was effectively fermented in cultures, resulting in similar efficiency of ruminal fermentation compared with the TF+NF. Data from this experiment imply that interseeding birdsfoot trefoil with TF may be a suitable sward to establish in a grazing experiment to further evaluate ruminal fermentation, nutrient utilization efficiency, and performance of grazing cattle.