This study evaluated which lipoprotein fractions are involved in C18:1 trans fatty acid (tFA) transport and whether there is a difference in transport between naturally occurring C18:1 tFA isomers [produced during rumen biohydrogenation of soybean oil (SO) or fish oil (FO)] and preformed tFA [supplied by partially hydrogenated vegetable oil (PHVO)]. Two non-lactating non-pregnant rumen fistulated cows (body weight ± SD = 778 ± 88 kg), were grouped in a 2 × 3 crossover design with 3 d rumen pulsing periods. Treatments were: 1) SO [control; 250 mL/d in 500 mL/d of skimmed milk (SM)]; 2) FO (250 g/d in 500 mL/d of SM) and 3) FO + PHVO (125 g/d FO + 125 g/d PHVO in 500 mL/d of SM). Treatments were supplied via rumen fistula. Fish oil increased C18:1 t9 concentration in high density lipoprotein triglyceride (HDL-TG) and low density lipoprotein triglyceride (LDL-TG). FO+PHVO increased C18:1 t9 concentration in very low density lipoprotein triglyceride (VLDL-TG). FO increased C18:1 t11 concentration in low density lipoprotein cholesterol esters (LDL-CE) and VLDL-TG. FO+PHVO increased C18:1 t11 concentration in VLDL-TG. Results showed that in bovine plasma there may be a differential transport mechanism in which the VLDL fraction is the main lipoprotein transporting tFA (primarily associated with TG) and is likely to be more responsive than other fractions to variation in supply of dietary tFA.