Milk saturated fatty acids, odd- and branched-chain fatty acids, and isomers of C18:1, C18:2, and C18:3n-3 according to their duodenal flows in dairy cows: A meta-analysis approach.

ABSTRACT

We sought to establish predictive response models of milk fatty acid (FA) yields or concentrations from their respective duodenal flow, rumen digestive parameters, or diet characteristics in dairy cows, with a special focus on cis and trans isomers of C181, C182, odd- and branched FA, and mammary de novo synthesized FA. This meta-analysis was carried out using data from trials with nature of forage, percentage of concentrate, supplementation of diets with vegetable oils or seeds, and marine products' animal fats as experimental factors. The data set included 34 published papers representing 50 experiments with 142 treatments. Increasing duodenal C18 FA flow induced a quadratic increase in milk total C18 yield and a linear decrease in milk C40 to C140 concentration. Intra-experimental predictive response models of individual milk cis C181 isomers (Δ 11 to 15 position) from their respective duodenal flows had coefficients of determination (R2) ranging from 0.74 to 0.99, with root mean square error varying from 0.19 to 0.96 g/d, 0.02 to 0.10% of total FA, and 0.03 to 0.29% of C18 FA. Models predicting milk trans C181 isomer yields or concentrations had R2 greater than 0.90 (except for trans-4 and trans-10 C181) with root mean square error varying from less than 0.1 to 5.2 g/d. Linear regressions for C182n-6, trans-10,cis-12 CLA, and trans-11,trans-13 CLA were calculated according to their respective duodenal flows. Quadratic models of milk C183n-3 yield or concentration from its duodenal flow had R2 values above 0.97. Models of amounts desaturated from C180 into cis-9 C181 and trans-11 C181 into cis-9,trans-11 CLA indicated that the contribution of C180 and trans-11 C181 desaturation to respective cis-9 C181 and cis-9,trans-11 CLA yields in milk fat was 83.8% (±0.75) and 86.8% (±2.8). Furthermore, when cows were fed marine products, our results could indicate a lower mammary uptake of C180 and trans-11 C181 in proportion to their respective duodenal flow, with no associated change in mammary Δ9-desaturase activity. Yields or concentrations of C150, C170, iso-C150, iso-C170, anteiso-C150, and anteiso-C170 were dependent on their respective duodenal flow or concentration at duodenum, but synthesis of these FA from C3 units for linear-chain odd FA, and from C2 units for branched-chain FA was suggested, respectively. Several milk C18 FA concentrations were closely related to their duodenal concentrations with slopes of the linear models close to the bisector; this could reflect a priority for the use of these duodenal C18 FA by the mammary gland to favor their high concentration in plasma triglycerides and nonesterified FA, which are preferentially taken up by the mammary gland.