Distribution of trans-vaccenic acid and cis9,trans11-conjugated linoleic acid (rumenic acid) in blood plasma lipid fractions and secretion in milk fat of Jersey cows fed canola or soybean oil

To determine fatty acid distribution in lipid fractions of bovine blood plasma, 24 multiparous Jersey cows at peak lactation were fed a control diet (no supplemental oil, NOS) or the control diet supplemented at 35 g·kg^-1 dry matter with canola oil (CAN), soybean oil (SOY), or a mixture of equal amounts of canola and soybean oil (MIX) for 4 wk. Plasma lipid fractions were isolated with aminopropyl columns. Fatty acid concentration in the phospholipid (PL), cholesterol ester (CE), and triglyceride (TG) fractions of plasma from cows fed supplemental oil was 142 (+47%), 144 (+57%), and 26 (+72%) μg·mL^-1 greater than those of the control group. Oleic acid increased from 153 to 195, 100 to 151, 35 to 53, and 103 to 161 mg·g^-1 of total fatty acids in the free fatty acid (FFA), PL, CE, and TG fractions, respectively, when CAN-fed cows were compared with NOS. In contrast, SOY intake increased 18:2n-6 in FFA, PL, CE, and TG fractions from 37 to 55, 327 to 366, 684 to 744, and 42 to 72 mg·g^-1, respectively. In the TG fraction, feeding SOY also increased trans11-18:1 from 40 to 105 mg·g^-1 and cis9,trans11-18:2 from 1 to 12 mg·g^-1. Concentration and yield of trans11-18:1 in milk fat were 21 mg·g^-1 and 13.7 g·d^-1 when feeding NOS, and increased to 45 mg·g^-1 and 43.1 g·d^-1 in response to SOY. Similarly, concentration and yield of cis9,trans11-18:2 were 5 mg·g^-1 and 7.3 g·d^-1, and increased to 13 mg·g^-1 and 11.2 g·d^-1 in response to SOY. Concentrations of trans-isomers in blood plasma and milk fat ranked by treatment reflected linoleic acid intakes, and were greater in SOY-fed cows compared with NOS or CAN-fed cows. Plasma lipid fractions can be used to appraise incomplete biohydrogenation of unsaturated fatty acids in the rumen.