Replacing hexane with 2-methyloxolane for defatting soybean meal fed to dairy cows: Effects on ruminal and milk fatty acid profiles and health indicators

Replacing hexane with 2-methyloxolane (MeOx) for defatting soybean meal (SBM) requires adaptations of the SBM production process. These modifications may increase the concentration of Maillard reaction products and reduce the residual oil content in MeOx-defatted SBM compared with hexane-defatted SBM. In addition, despite desolventization, solvent residues may still be present in the SBM when fed to livestock. This study aims to ensure that the replacement of hexane with MeOx for defatting SBM does not affect the ruminal and milk fatty acid profiles nor the liver activity, liver functionality, and inflammatory status in dairy cows. A 4 × 4 Latin square design experiment was conducted with 16 primiparous dairy cows that received 4 dietary treatments: 100% hexane-defatted SBM (control diet, HEX), 67% hexane-defatted SBM plus 33% MeOx-defatted SBM (33MeOx), 33% hexane-defatted SBM plus 67% MeOx-defatted SBM (67MeOx), and 100% MeOx-defatted SBM (100MeOx). Diets contained 16% SBM on a DM basis and were iso-CP and iso-net energy. We collected feed, ruminal content, blood, and milk samples. We measured traits related to lipid digestion in the rumen and secretion in milk (feed, ruminal, and milk fatty acid profiles), energy metabolism (plasma acetate, BHB, nonesterified fatty acids, and glucose concentrations, as well as C isotopic discrimination between plasma and diet), liver integrity and functionality (plasma enzyme activities and serum albumin and plasma total bilirubin concentrations), and inflammatory status (blood cell counts and plasma cytokine concentrations). We used difference and equivalence tests for statistical analyses. Replacing HEX with 100MeOx resulted in likely equivalent milk fat content, fat yield, and major fatty acid profile. Stearyl-CoA desaturase activity in the mammary gland, indicated by the C14:1 cis-9-to-C14:0 ratio, was negatively linearly related to the proportion of MeOx-defatted SBM in the diet. We did not find evidence of strict equivalence between 100MeOx and HEX in ruminal fatty acid profile. However, only minor differences were observed. Plasma γ-glutamyltransferase, aspartate aminotransferase, and alanine aminotransferase activities, as well as total bilirubin concentration, were unlikely equivalent toward greater values with 100MeOx compared with HEX, suggesting slight changes in liver integrity and functionality with 100MeOx. The overall inflammatory status of dairy cows was unlikely equivalent between 100MeOx and HEX. However, significant differences were limited to blood basophil count and plasma chemokine C-C motif ligand 4 concentration that were negatively linearly related to the proportion of MeOx-defatted SBM in the diet, and plasma chemokine C-X-C motif ligand 8 concentration that was quadratically related to the proportion of MeOx-defatted SBM in the diet. Altogether, these results indicate that the replacement of hexane-defatted SBM with MeOx-defatted SBM in the diet of dairy cows resulted in likely equivalent lipid secretion in milk despite a slight reduction in stearyl-CoA desaturase activity in the mammary gland with MeOx-defatted SBM. In the context of this study (i.e., short-term exposure, high level of MeOx, low level of hexane), neither hexane-defatted SBM nor MeOx-defatted SBM impaired health, but slight changes in some indicators of liver integrity, liver functionality, and inflammatory profile may warrant further investigation (e.g., long-term exposure).