Myristic acid supports the immediate inhibitory effect of lauric acid on ruminal methanogens and methane release.

Two in vitro experiments were carried out with the Hohenheim gas test (HGT) apparatus in order to investigate dose-dependent effects and interactions of non-esterified lauric acid (C(12)) and myristic acid (C(14)) given either individually or in mixture on ruminal methanogens and methanogenesis. Special emphasis was also put on the relationship between effects on methane formation and methanogenic counts. The in vitro incubations were conducted in 10mL ruminal fluid and 20mL buffer solution and lasted for 24h. In the first experiment, 14 levels of C(12), C(14) and stearic acid (C(18); control) were supplied each in increasing steps of 2.5mg covering the range from 0 to 32.5mg. In the second experiment, dosages ranging from 2.5 to 30mg C(12) were supplemented in steps of 2.5mg either without or with 10, 20 or 30mg of C(14). Counts of total Archaea and individual methanogenic orders were determined by the fluorescence in situ hybridization technique using 16S rRNA oligonucleotide probes. In experiment 1, a methane-suppressing effect of more than 80% was achieved with a supply of 30mg C(12), whereas C(14) and C(18) had no effect. Incubation liquid counts of total Archaea and individual methanogenic orders (Methanococcales, Methanosarcinales, Methanomicrobiales and Methanobacteriales) exponentially decreased as a response to C(12) and C(14) to about the same degree (up to 90%) and, to a lesser extent, by C(18). The proportions of the orders of total methanogenic population were not altered by any of the fatty acids. In experiment 2, an additional supply of 10 or 20mg of C(14) supported the suppression of methanogenesis and methanogens by C(12) synergistically. Supplementing 30mg instead of 20mg of C(14) did not further increase the efficacy of C(12) in suppressing methane formation and methanogens. The study illustrated the advantage of using mixtures of C(12) and C(14) in ruminant nutrition to suppress methane emission since mixtures will reduce the amounts of the less palatable C(12) required in feed.