Effects of sunflower oil infusions of Asparagopsis taxiformis on in vitro ruminal methane production and biohydrogenation of polyunsaturated fatty acids
Filipa V. Sena, P.V. Portugal, M.T. Dentinho, K. Paulos, Camila Fraga da Costa, D.M. Soares, A. Oliveira, H. Ramos, Susana P. Alves, José Santos‐Silva, R.J.B. Bessa
Abstract
Asparagopsis taxiformis inhibits ruminal methane (CH 4 ) production due to its bromoform (CHBr 3 ) content. The immersion of A. taxiformis in edible vegetable oils allows the extraction and stabilization of the highly volatile CHBr 3 in the oil phase. The objectives of this study were to explore the effects of adding sunflower oils with increasing concentrations of CHBr 3 on in vitro ruminal methanogenesis and biohydrogenation. Five 48h in vitro batch incubations were performed in 14 fermentation bottles, using a total mixed ration diet as substrate, ruminal liquid from crossbred young bulls collected shortly after slaughter, without adding oil (Control) or with 60 μL of sunflower oil per g of substrate dry matter (DM) (1 g DM of substrate was used). The treatments were the CHBr 3 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 3 per gram of substrate DM, supplied in 60 μL of oil. Organic matter degradability (OMD), total gas, CH 4 , volatile fatty acids (VFA), long-chain fatty acids (FA), 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 Control and was unaffected by CHBr 3 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 3 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 3 -containing treatments, although without any dose-response pattern. The molar percentage of acetate decreased linearly while propionate and butyrate increased linearly with the increasing CHBr 3 dosage. Including oil in the diet decreased the branched-chain FA and DMA content. Increasing CHBr 3 concentrations did not affect branched-chain FA 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 3 had no effect on 18:2n-6 but decreased linearly the 18:0 and increased the trans -18:1. The results obtained provide evidence that oil immersions of A. taxiformis can successfully inhibit ruminal production of CH 4 in vitro at doses of 100 and 150 μg/g DM, and simultaneously modulate biohydrogenation.