Using krabok (Irvingia malayana) seed oil and Flemingia macrophylla leaf meal as a rumen enhancer in an in vitro gas production system

An in vitro gas production system was conducted to investigate the effect of krabok (Irvingia malayana) seed oil (KSO) and Flemingia (Flemingia macrophylla) leaf powder (FLM) supplementation on gas production kinetics, volatile fatty acid (VFA) and methane production with different ratios of rice straw to cassava chip (RS : CC). The treatments were arranged according to a 4 × 2 × 2 factorial arrangement in a completely randomised design using four different ratios of RS : CC (100 : 0; 60 : 40; 20 : 80; and 0 : 100), two levels of KSO supplement (0% and 2.5% of total dietary substrate) and two levels of FLM supplement (0% and 2.5% of total dietary substrate). The gas production kinetics were affected by RS : CC, KSO and FLM supplementation (P < 0.05). However, there was no interaction between RS : CC*FLM, FLM*KSO, or RS : CC*FLM*KSO; with the exception of RS : CC*KSO (P < 0.05). Cumulative gas at 96 h post incubation was increased with increasing RS : CC especially at 0 : 100. However, KSO supplementation suppressed gas production whereas FLM could enhance gas production from feed fraction (P < 0.05). Increasing RS : CC ratio resulted in increasing total VFA, propionic acid and butyric acid whereas acetic acid concentration was reduced; therefore, ratio of acetic acid : propionic acid was reduced. However, KSO supplementation depressed VFA production whereas the FLM supplement had no effect. The methane production was reduced with increasing level of RS : CC especially with supplementation of KSO. Based on this study, it is concluded that KSO addition could reduce methane production whereas FLM could enhance the gas production and fermentation end products; hence, the combined use is potentially beneficial. However, further research under in vivo conditions should be conducted.