title: Duodenal and milk trans octadecenoic acid and conjugated linoleic acid (CLA) isomers indicate that postabsorptive synthesis is the predominant source of cis-9-containing CLA in lactating dairy cows.
abstract: Duodenal and milk samples obtained from lactating cows in a previous study were analyzed to compare the content and isomer distribution of conjugated linoleic acids (CLA) and trans-18:1 fatty acids (tFA). Four diets containing either low [25 g/100 g dry matter (DM)] or high (60 g/100 g DM) forage were fed with or without 2% added buffer to four multiparous Holstein dairy cows in a 2 x 2 factorial, 4 x 4 Latin square design with 3-wk experimental periods. Duodenal flows of CLA were low (1.02-1.84 g/d), compared with that of tFA (57-120 g/d), regardless of diet. The greatest amounts of CLA and tFA, as well as the greatest proportions of trans-10-18:1 (P < 0.02), and cis-9, trans-11 (P < 0.01) and trans-10, cis-12 CLA (P < 0.01) were in the duodenal flow of cows fed the low forage unbuffered diet. In milk fat, tFA were increased by the low forage unbuffered diet and the trans-10-18:1 (P < 0.02) replaced trans-11-18:1 as the major 18:1 isomer. Milk CLA secretion (7.2-9.1 g/d) was greater (P < 0.001) than that in the duodenal flow with each diet. This was due to the increase in cis-9, trans-11-18:2 and trans-7, cis-9 CLA, resulting most likely from endogenous synthesis via Delta9-desaturation of ruminally derived tFA. For other CLA isomers, duodenal flow was always greater than milk secretion, suggesting that they essentially were produced in the rumen.
authors.affiliation: Animal and Avian Sciences Department, University of Maryland, College Park, MD 20742, U.S.A.
authors.forename: Liliana S
authors.initials: LS
authors.lastname: Piperova
authors.forename: Joseph
authors.initials: J
authors.lastname: Sampugna
authors.forename: Beverly B
authors.initials: BB
authors.lastname: Teter
authors.forename: Kenneth F
authors.initials: KF
authors.lastname: Kalscheur
authors.forename: Martin P
authors.initials: MP
authors.lastname: Yurawecz
authors.forename: Youh
authors.initials: Y
authors.lastname: Ku
authors.forename: Kim M
authors.initials: KM
authors.lastname: Morehouse
authors.forename: Richard A
authors.initials: RA
authors.lastname: Erdman
mesh_terms: D000821:Animal Feed; D000818:Animals; D002417:Cattle / Q000378:metabolism* / Q000502:physiology; D003612:Dairying; D004386:Duodenum / Q000378:metabolism*; D005227:Fatty Acids / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D005260:Female; D007536:Isomerism; D007774:Lactation / Q000378:metabolism* / Q000502:physiology; D008041:Linoleic Acids / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D008892:Milk / Q000737:chemistry*; D012417:Rumen / Q000378:metabolism; D013229:Stearic Acids / Q000032:analysis / Q000378:metabolism*
chemical_list: C114874:5-octadecenoic acid; D005227:Fatty Acids; D008041:Linoleic Acids; D013229:Stearic Acids