Assessment of in vitro fermentation characteristics of lactation dairy diets consisting of orchardgrass or birdsfoot trefoil pasture forages with different supplements using continuous cultures

Abstract Text: This study evaluated the effects of feeding 2 different pasture forages [orchardgrass (OG) vs. birdsfoot trefoil (BFT)] combined with 3 supplements [no supplement, ground barley (GB), and forage-concentrate mixture (FCMX)] on in vitro fermentation characteristics. The experiment was performed in a 2 (source of pasture forage) × 3 (supplement) factorial design with 3 independent runs of continuous cultures (n = 3). Continuous culture apparatus consisted of 700-mL working volume fermentation vessels to measure major fermentation end-products. Each culture was offered a diet of 15 g DM/d in 4 equal portions at 0600, 1200, 1800, and 2400 h, and the supplements (GB and FCMX) were included at 30% DM of total diets. Culture pH averaged 6.15 and was not different across treatments. Total VFA concentration averaged 39.5 mM and did not differ among treatments. Feeding different pasture forages did not influence acetate and propionate concentrations. While acetate concentration was similar across treatments, propionate concentration increased with supplementing GB or FCMX, resulting in a decreased acetate-to-propionate ratio due to the supplementations. Ammonia-N concentration tended to decrease (P < 0.06) with BFT compared with OG (9.40 vs. 13.5 mg/100 mL), whereas supplementation resulted in no difference in the ammonia-N concentration, regardless of source of pasture forage. Methane production decreased when fermentors were offered BFT compared with OG (8.50 vs. 10.9 mmol/d), but supplementation did not affect the methane production under OG as well as BFT. The positive impacts of feeding BFT pasture forage with decreased ammonia-N and methane concentrations could have resulted from beneficial effects of condensed tannins (4.46% DM) in BFT which manipulate ruminal fermentation pathways by improving utilization of N and energy substrates. Overall results in this experiment indicate that feeding BFT-based dairy diets did not interfere with in vitro ruminal fermentation, and BFT can be an effective forage source to reduce N excretion and mitigate methane emissions.

Keywords: birdsfoot trefoil, condensed tannins, continuous cultures