Effect of the supplementation of fish oil on the conjugated linoleic acid production, especially accumulation of trans-11 C18:1 and trans-10 C18:1 fatty acids: An in vitro rumen fermentation study

This study was aimed to investigate the effects of fish oil supplementation on production of CLA species, and accumulation of trans-11 C18:1 and trans-10 C18:1 in the rumen. Ruminal fluid was collected from goats, diluted in acidic incubation buffer, and then incubated with a mixture of dry grass and concentrate supplemented with soybean oil and different amounts of fish oil (0, 50, and 100 mg for the control, LFO, and HFO groups, respectively). Incubation was carried out anaerobically at 39 °C for 24 h, and fatty acid composition was analyzed by chromatography at different time points. Although it showed initial inhibitory effects at earlier time points, fish oil significantly increased cis-9, trans-11 CLA content at 24 h. At the same time, it inhibited trans-10, cis-12 CLA content dose-dependently with significant effect at 16 and 24 h. Fish oil also increased trans-11 C18:1 content significantly (P < 0.05) but decreased trans-10 C18:1 content (P < 0.01) at 16 h and 24 h. It caused a significant increase of oleic acid content (P < 0.01) at 8 h, 16 h and 24 h, and decreased fraction of stearic acid (P < 0.001) at all the time points. After 16 h incubation, fish oil also significantly (P < 0.05) increased the amount of trans-11 C18:1 + cis-9, trans-11 CLA but significantly (P < 0.05) reduced the amount of trans-10 C18:1 + trans-10, cis-12 CLA. Together, our results showed that fish oil supplementation can significantly increase the production of cis-9, trans-11 CLA and trans-11 C18:1, and lower the amount of trans-10 C18:1 and trans-10, cis-12 CLA in the ruminal fluid.