Strategies to modify the ruminal biohydrogenation of polyunsaturated fatty acids and the production of trans-10, cis-12 C18:2 in vitro

The production of trans-10, cis-12 C18:2 isomer in the rumen is associated with milk fat depression. Two experiments were conducted to determine the effects of some additives on rumen fermentation and apparent biohydrogenation of linoleic (LA) and linolenic (LNA) acids, and the production of the trans-10, cis-12 C18:2 isomer associated with milk fat depression. In experiment 1, a 1:1 forage:concentrate diet containing linseed oil (84 g/kg of DM) was incubated in a 2 h or 6 h batch culture with rumen fluid in 2 replicated periods. Treatments in the 2 h incubations were: control; lipase 1 and 2 (4 and 40 μl/l) and a lipase inhibitor (4 and 20 mg/l); and in the 6 h incubations were: Oxy-propyl-thiosulfate (PTSO; 60 and 120 mg/l); Eugenol (EUG; 150 and 500 mg/l) and Cinnamaldehyde (CIN; 150 and 500 mg/l). After incubation, samples were collected to analyze ammonia-N, volatile fatty acids (VFA) and the fatty acid (FA) profile. In experiment 2, 8 continuous culture fermenters (1320 ml) were used in 3 replicated periods (5 d of adaptation and 3 d of sampling). Fermenters were fed 95 g/d of DM of a 60:40 forage:concentrate diet containing 50 g/kg DM of linseed oil. Treatments were control, lipase 1 (4 μl/l), PTSO (90 mg/l) and CIN (250 mg/l), and were tested at 2 pH levels (6.4 and 5.6). During the last 3 d of each period, samples were taken to analyze VFA, ammonia-N and the FA profile. In experiment 1, Lipase 1 increased the apparent biohydrogenation of LNA, but these results were not observed in experiment 2. Both CIN and PTSO seem to inhibit the apparent biohydrogenation of LNA, but only the PTSO inhibited the biohydrogenation of LA in a 6 h incubation compared with control. Cinnamaldehyde in Experiment 1, and PTSO in Experiment 1 and 2 decreased total VFA concentrations. Although the short-term batch incubation suggested some potential benefits of use of some additives for modifying rumen biohydrogenation pathways, effects observed in the long-term fermentation were not relevant for the purpose of decreasing the production of trans-10, cis-12 C18:2 isomer involved in milk fat depression.