title: Evaluating the conjugated linoleic acid and trans 18:1 isomers in milk fat of dairy cows fed increasing amounts of sunflower oil and a constant level of fish oil.
abstract: The objective was to evaluate different levels of sun-flower oil (SFO) in dairy rations to increase vaccenic (trans-11-18:1) and rumenic acids (cis-9,trans-11-18:2) in milk fat, and assess the content and composition of other trans-octadecenoic (trans-18:1) and conjugated linoleic acids (CLA) isomers. Eighty lactating Holstein cows were fed control diets for 4 wk and then placed on 4 diets for 38 d; milk fat was analyzed after 10 and 38 d. The treatments were: control, 1.5% SFO plus 0.5% fish oil (FO), 3% SFO plus 0.5% FO, and 4.5% SFO plus 0.5% FO. The forage-to-concentrate ratio was 50:50 and consisted of barley/alfalfa/hay silage and corn/barley grain concentrate. There were no differences in milk production. Supplementation of SFO/FO reduced milk fat compared with respective pretreatment periods, but milk protein and lactose levels were not affected. There was a linear decrease in all short- and medium-chain saturated fatty acids (SFA) in milk fat after 10 d (25.5, 24.1, 20.2, and 16.7%) and a corresponding linear increase in total trans-18:1 (5.2, 9.1, 14.1, and 21.3%) and total CLA (0.7, 1.9, 2.4, and 3.9%). The other FA in milk fat were not affected. Separation of trans-18:1 isomers was achieved by combination of gas chromatography (GC; 100-m highly polar capillary column) and prior separation of trans FA by silver ion-thin layer chromatography followed by GC. The CLA isomers were resolved by a combination of GC and silver ion-HPLC. The trans-11- and trans-10-18:1 isomers accounted for approximately 50% of the total trans-18:1 increase when SFO/FO diets were fed. On continued feeding to 38 d, trans-11-18:1 increased with 1.5% SFO/FO, stayed the same with 3%, and declined with 4.5% SFO/FO. Rumenic acid showed a similar pattern on continued feeding as trans-11-18:2; levels increased to 0.43, 1.5, 1.9, and 3.4% at 10 d and to 0.42, 2.15, 2.09, and 2.78% at 38 d. Rumenic acid was the major CLA isomer in all 4 diets: 66, 77, 78 and 85%. The CLA isomers trans-7,cis-9-, trans-9,cis-11-, trans-10,cis-12-, trans-11,trans-13-, and trans-9,trans-11-/trans-10,trans-12-18:2 also increased from 0.18 (control) to 0.52% (4.5% SFO/FO). Milk fat produced from 3% SFO/FO appeared most promising: trans-11-18:1 and cis-9,trans-11-18:2 increased 4.5-fold, total SFA reduced 18%, and moderate levels of trans-10-18:1 (3.2%), other trans-18:1 (6.6%) and CLA isomers (0.5%) were observed, and that composition remained unchanged to 38 d. The 4.5% SFO/FO diet produced higher levels of trans-11-18:1 and cis-9,trans-11-18:2, a 28% reduction in SFA, and similar levels of other trans-18:1 (9.2%) and CLA isomers (0.52%), but the higher levels of trans-11-18:1 and cis-9,trans-11-18:2 were not sustained. A stable milk fat quality was achieved by feeding moderate amounts of SFO (3% of DM) in the presence of 0.5% FO that had 4% vaccenic and 2% rumenic acids.
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, Alberta, 4-10 Agriculture/Forestry Centre, Edmonton, Alberta, Canada, T6G-2P5.
authors.forename: C
authors.initials: C
authors.lastname: Cruz-Hernandez
authors.forename: J K G
authors.initials: JK
authors.lastname: Kramer
authors.forename: J J
authors.initials: JJ
authors.lastname: Kennelly
authors.forename: D R
authors.initials: DR
authors.lastname: Glimm
authors.forename: B M
authors.initials: BM
authors.lastname: Sorensen
authors.forename: E K
authors.initials: EK
authors.lastname: Okine
authors.forename: L A
authors.initials: LA
authors.lastname: Goonewardene
authors.forename: R J
authors.initials: RJ
authors.lastname: Weselake
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004032:Diet / Q000662:veterinary; D019587:Dietary Supplements; D005223:Fats / Q000032:analysis; D005229:Fatty Acids, Monounsaturated / Q000032:analysis; D005231:Fatty Acids, Unsaturated / Q000032:analysis; D005260:Female; D005395:Fish Oils / Q000008:administration & dosage* / Q000378:metabolism; D007536:Isomerism; D007774:Lactation; D044243:Linoleic Acids, Conjugated / Q000032:analysis; D008892:Milk / Q000737:chemistry*; D010938:Plant Oils / Q000008:administration & dosage* / Q000378:metabolism; D011897:Random Allocation; D000074242:Sunflower Oil; D044242:Trans Fatty Acids / Q000032:analysis
chemical_list: D005223:Fats; D005229:Fatty Acids, Monounsaturated; D005231:Fatty Acids, Unsaturated; D005395:Fish Oils; D044243:Linoleic Acids, Conjugated; D010938:Plant Oils; D000074242:Sunflower Oil; D044242:Trans Fatty Acids