Dietary canola or soybean oil with two levels of conjugated linoleic acids (CLA) alter profiles of 18:1 and 18:2 isomers in blood plasma and milk fat from dairy cows

To determine responses of enhanced ruminal supply of oleic or linoleic acid in combination with conjugated linoleic acids (CLAs) on blood plasma and milk fatty acid profiles, four Holstein cows were fed diets containing supplemental (30 g/kg dry matter) canola oil (CAN) or soybean oil (SOY), and CAN plus (4 g/kg dry matter) CLA (90% pure) (CCLA) or SOY plus CLA (SCLA). A 4×4 Latin square design was used during 7-day experimental periods. Milk yield, dry matter intake, and percentages and yields of fat and protein in milk were not affected by treatments. Oleic acid intake when CAN or CCLA were fed, compared with SOY or SCLA, was 472 g per day greater. In contrast, linoleic acid intake was 362 g per day greater due to feeding SOY or SCLA. Intake of cis9,trans11-18:2 and trans10,cis12-18:2 averaged 28 and 30 g per day for CCLA or SCLA-fed cows (P=0.01). Concentration (μg/ml) of trans9-18:1 in blood plasma was 34% greater (P=0.01) due to feeding CAN or CCLA compared with SOY or SCLA. In contrast, feeding SOY or SCLA increased (P≤0.05) trans11-(+53%), trans12-(+18%), and trans16-18:1 (+33%) concentrations. Dietary CLA, regardless of oil, increased (P=0.05) (+25%) trans10-18:1 concentration. Trans10,cis12-18:2 also increased (P=0.01) from not detectable levels to 2 μg/ml due to feeding CLA. Greater (P=0.01) concentrations of trans11-, trans12-, trans13/14-, and trans16-18:1 in milk fat when SOY or SCLA were fed, compared with CAN or CCLA, led to greater yields in milk. Concentration and yield of trans9-18:1, however, were greater (P=0.01) in response to feeding CAN or CCLA. Trans10-18:1 concentration and yield increased (P≤0.05) 27 and 17% when CLA was fed with either oil. Concentration and yield of cis9,trans11-18:2 in milk fat were greater (P=0.01) due to SOY (7 mg/g, 8 g per day) compared with CAN (5 mg/g, 6 g per day). Supplemental CLA did not affect (P=0.08) cis9,trans11-18:2 concentration, but reduced (P=0.02) its yield in milk exclusively when fed with soybean oil. Trans10,cis12-18:2 increased (P=0.01) from not detectable levels when CAN or SOY were fed to 1 mg/g and 1 g per day in response to CLA. Results suggest isomerization of cis9-18:1 in the rumen increased output of trans9-18:1. Hydrogenation of 18:2n-6, however, increased ruminal production of trans11-18:1 and its bioconversion to cis9,trans11-18:2 in the mammary gland. Dietary CLA were extensively hydrogenated, but the extent of hydrogenation appeared lower for trans10,cis12-18:2.