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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

cis-9, trans-11 Conjugated Linoleic Acid Is Synthesized Directly from Vaccenic Acid in Lactating Dairy Cattle^1,2

Erin E. Mosley^*, Bahman Shafii, Peter J. Moate^** and Mark A. McGuire^*,3

^* Department of Animal and Veterinary Science, College of Agricultural and Life Sciences, University of Idaho, Moscow, ID 83844-2330; Statistical Programs, College of Agricultural and Life Sciences, University of Idaho, Moscow, ID 83844-2337; and ^** Department of Clinical Studies, University of Pennsylvania, Philadelphia, PA 19348

³ To whom correspondence should be addressed. E-mail: mmcguire{at}uidaho.edu.

The utilization of ¹³C-labeled vaccenic acid (VA) by lactating dairy cows to synthesize cis-9, trans-11 conjugated linoleic acid (CLA) was investigated. Primiparous ruminally cannulated Holstein cows (n = 3) were abomasally infused with 1.5 g of VA-1-¹³C. Blood and milk samples were taken frequently before and after VA infusion. Milk and plasma lipid were extracted using chloroform:methanol. Plasma lipid was separated into triacylglycerol (TG), cholesterol ester (CE), phospholipid (PL), nonesterified fatty acid (NEFA), and mono- and diacylglycerol (MDG) fractions. Lipid was methylated, converted to dimethyl disulfide and Diels-Alder adducts, and analyzed by GC-MS. Increased enrichment of ¹³C was determined using a 2-sample t test for each sample time compared with –24 h, with significance declared at P < 0.05. Enrichment in milk fat VA was detected at 4 (3.0%), 8 (8.3%), 12 (4.1%), 16 (2.2%), and 20 h (0.8%). Enrichment in VA was also detected in plasma TG, NEFA, PL, and MDG. Enrichment in milk fat cis-9, trans-11 CLA, the 9-desaturase product of VA, was detected at 4 (2.6%), 8 (6.6%), 12 (3.4%), 16 (1.7%), and 24 h (0.7%). Enrichment was not detected in cis-9, trans-11 CLA for any plasma lipid fraction. Modeling of the data showed the exponential decay in ¹³C enrichment over time for both VA and cis-9, trans-11 CLA in milk fat. Conversion of dietary VA to cis-9, trans-11 CLA endogenously was confirmed with the mammary gland being the primary site of 9-desaturase activity; 80% of milk fat cis-9, trans-11 CLA originated from VA.

KEY WORDS: • vaccenic acid • cis-9, trans-11 conjugated linoleic acid • desaturase • milk fat

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