Abstract

Dietary fatty acids (FA) are transferred directly to milk through chylomicrons and indirectly through tissue recycling. The objective of this study was to characterize the transfer kinetics of the CLA isomers cis-9, trans-11 (c9t11) and trans-10, cis-12 (t10c12) to plasma and milk, and determine direct and indirect transfer rates to milk, following a single abomasal bolus infusion. Five ruminally cannulated multiparous mid-lactation cows (148 ± 86 days in milk; 44.1 ± 11.2 kg/d) received a single abomasal bolus infusion of an enriched CLA mixture providing 15 g of each CLA isomer (c9t11, t10c12), over a 30 min period. Total transfer of CLA was analyzed in a model that included cow as a random effect and CLA isomer as fixed effect (JMP Pro). Time course data was analyzed as repeated measures in SAS and resulting least-square means were fit to a double exponential decay function by non-linear curve fitting (JMP Pro) to determine direct and indirect transfer of CLA isomers to milk. Plasma concentration of t10c12 peaked at 2 h reaching 0.32 and 0.31 % of plasma FA for c9t11 and t10c12, respectively, and returned to baseline at 72 h. Milk t10c12 concentration peaked at 14 h (0.5 %) and returned to baseline at 86 h post infusion. Milk c9t11 concentration peaked at 14 h (0.98 %) and dropped to baseline at 86 h post infusion, and then reached a second peak between 146 to 158 h (0.56 %) post infusion. Total transfer of CLA to milk differed between isomers and was 79.3 and 40.8 % of the bolus for c9t11 and t10c12, respectively (P < 0.001). Time course of CLA isomers transferred to milk fit a biexponential model (R2=0.99). The area (% of total) under the first exponential representing direct transfer was 17 and 73 % and the second exponential representing indirect transfer was 83 and 27 % of the total CLA isomers transferred for c9t11 and t10c12, respectively. In conclusion, although plasma kinetics of c9t11 and t10c12 were similar, transfer of CLA isomers to milk differed greatly in their transfer efficiency and mayor pool of transfer.