title: Trans-7,cis-9 CLA is synthesized endogenously by delta9-desaturase in dairy cows.
abstract: Cis-9,trans-11 and trans-7,cis-9 CLA are the most prevalent CLA isomers in milkfat. The majority of cis-9,trans-11 CLA is synthesized endogenously by delta9-desaturase. We tested the hypothesis that trans-7,cis-9 CLA originates from endogenous synthesis by inhibiting delta9-desaturase with a source of cyclopropene FA (sterculic oil: SO) or with a trans-10,cis-12 CLA supplement. Experiment 1 (four cows; Latin square) involved four treatments: control, SO, partially hydrogenated vegetable oil (PHVO), and PHVO + SO. Milk, plasma, and rumen fluid were collected. Experiment 2 treatments (four cows) were 0 or 14.0 g/d of 10,12 CLA supplement; milk and plasma were collected. Samples were analyzed by GC and Ag+-HPLC to determine FA. In Experiment 1, SO decreased milkfat content of trans-7,cis-9 CLA by 68 to 71% and cis-9,trans-11 CLA by 61 to 65%. In Experiment 2, the 10,12 CLA supplement decreased milkfat content of trans-7,cis-9 CLA and cis-9,trans-11 by 44 and 25%, respectively. Correcting for the extent of treatment-induced inhibition of delta9-desaturase based on changes in myristic and myristoleic acids, endogenous synthesis of trans-7,cis-9 CLA represented 85 and 102% in Experiments 1 and 2, respectively. Similar corrected values were 77 and 58% for endogenous synthesis of cis-9,trans-11 CLA. Thus, milkfat cis-9,trans-11 CLA was primarily from endogenous synthesis with a minor portion from rumen escape. In contrast, trans-7,cis-9 CLA was not present in rumen fluid in significant amounts. Results indicate this isomer in milkfat is derived almost exclusively from endogenous synthesis via delta9-desaturase.
authors.affiliation: Department of Animal Science, Cornell University, Ithaca, New York, USA.
authors.forename: Benjamin A
authors.initials: BA
authors.lastname: Corl
authors.forename: Lance H
authors.initials: LH
authors.lastname: Baumgard
authors.forename: J Mikko
authors.initials: JM
authors.lastname: Griinari
authors.forename: Pierluigi
authors.initials: P
authors.lastname: Delmonte
authors.forename: Kim M
authors.initials: KM
authors.lastname: Morehouse
authors.forename: Martin P
authors.initials: MP
authors.lastname: Yurawecz
authors.forename: Dale E
authors.initials: DE
authors.lastname: Bauman
mesh_terms: D000818:Animals; D002417:Cattle; D003612:Dairying; D044943:Fatty Acid Desaturases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005260:Female; D007536:Isomerism; D007774:Lactation / Q000378:metabolism; D019787:Linoleic Acid / Q000032:analysis / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D008892:Milk / Q000737:chemistry*; D010938:Plant Oils / Q000737:chemistry; D013230:Stearoyl-CoA Desaturase
chemical_list: D010938:Plant Oils; D019787:Linoleic Acid; D044943:Fatty Acid Desaturases; D013230:Stearoyl-CoA Desaturase; C029627:delta-9 fatty acid desaturase