Effect of microbial oil, monensin and fumarate on rumen fermentation in artificial rumen

The objective of this study was to investigate the effect of microbial oil on rumen fermentation of a diet composed of 60% hay and 40% barley in an artificial rumen (Rusitec). Microbial oil (MO) was produced by the fungus Thamnidium elegans. This fungus grew on the wheat bran/spent malt grains (3:1) mixture. The fatty acid composition of microbial oil was as follows: 0.7% C14:0, 15.4% C16:0, 10.1% C18:0, 50.9% C18:1, 13.9% C18:2 and 8.4% C18:3 (GLA, γ-linolenic acid). The effect of monensin MON (66 ppm) and fumarate FUM (6.25 mmol) with and without MO supplementation was also studied. The experiment in Rusitec lasted 11 days. After a stabilization period (5 days), MO was added to fermentation vessel V2 (6 days), MON to fermentation vessel V3 (6 days) and FUM to fermentation vessel V4 (6 days). MO was also added to V3 and V4 on the last day together with MON (V3) and FUM (V4). The fermentation vessel V1 served as control (without additives). The results showed that MO reduced (P < 0.05) mol% acetate and increased (P < 0.05) mol% propionate and n-butyrate. Methane production (mmol/day) was reduced numerically (NS). The efficiency of microbial synthesis (EMS) was also reduced numerically and nitrogen incorporated by the microflora (NM) was reduced significantly in MO supplementation. There were no differences in the rumen fermentation when MO was applied together with MON and FUM compared to the vessel where only MO was applied. No additive effect was observed in the relationship MO-ionophore or MO-FUM. Monensin and fumarate applied separately showed their typical effects on rumen fermentation in vitro.