Effects of sunflower oil infusions of Asparagopsis taxiformis on in vitro ruminal methane production and biohydrogenation of polyunsaturated fatty acids.

Asparagopsis taxiformis inhibits ruminal methane (CH) production due to its bromoform (CHBr) content. The immersion of A. taxiformis in edible vegetable oils allows the extraction and stabilization of the highly volatile CHBr in the oil phase. The objectives of this study were to explore the effects of adding sunflower oils with increasing concentrations of CHBr on in vitro ruminal methanogenesis and biohydrogenation. Five batches of 48-h in vitro incubations were performed in 14 fermentation bottles, using rumen inocula collected shortly after the slaughter of young crossbred bulls and 1 g of dry matter (DM) from a total diet of mixed feed without added oil (control) or with 60 μL of sunflower oil per gram of DM as the substrate. The treatments were the CHBr content in the oil added: 0 μg (B0), 25 μg (B25), 50 μg (B50), 75 μg (B75), 100 μg (B100), and 150 μg (B150) of CHBr per gram of substrate DM. Organic matter (OM) degradability, total gas, CH, volatile fatty acids (VFA), long-chain fatty acids, and dimethyl acetals (DMA) were analyzed at the end of each incubation. Data were analyzed with a model considering the treatments as the fixed effect and the run as a random block and using orthogonal contrasts. Degradability of OM was higher in the control group and was unaffected by CHBr concentration. Total gas production per gram of degraded OM was unaffected by treatments and averaged 205 ± 29.8 mL/g. Methane (mL) production decreased linearly with increasing CHBr concentrations, with 33%, 47%, and 87% reductions for B75, B100, and B150, respectively. Total VFA concentration was unaffected by oil inclusion but was reduced by 20% in CHBr-containing treatments, although without any dose-response pattern. The molar percentage of acetate decreased linearly, whereas propionate and butyrate increased linearly with the increasing CHBr dosage. Including oil in the diet decreased the branched-chain fatty acids and DMA content. Increasing CHBr concentrations did not affect branched-chain fatty acids, but linearly increased most of the identified DMA. Adding oil to the control diet increased the 18:2n-6, whereas increasing the concentration of CHBr had no effect on 18:2n-6 but decreased linearly the 18:0 and increased the trans-18:1 isomers. The results obtained provide evidence that oil immersions of A. taxiformis can successfully inhibit ruminal production of CH in vitro at doses of 100 and 150 μg/g DM, and simultaneously modulate biohydrogenation.