title: A comparison between feeding systems (pasture and TMR) and the effect of vitamin E supplementation on plasma and milk fatty acid profiles in dairy cows.
abstract: Unidentified constituents in fresh pasture increase milk fat cis-9, trans-11 conjugated linoleic acid (CLA) concentration, and prevent milk fat depression, even though ruminal conditions conducive to reducing milk fat synthesis exist. One possible explanation is vitamin E (kappa-tocopherol), a constituent high in fresh pasture, but naturally low in conserved/dried forages and cereal grains. Twenty late-lactating dairy cows previously consuming a total mixed ration (TMR) were randomly allocated to one of two dietary treatments for 21 d: TMR (control; n=10); and TMR plus an additional 10,000 i.u. alpha-tocopherol/d (VIT E; n = 10). These cows were simultaneously compared with 13 late-lactation dairy cows previously grazing fresh pasture (PAS) balanced for age, parity and genetic merit. Average daily alpha-tocopherol intakes were approximately 468, 10,520 and 1,590 i.u./cow for the control, VIT E and PAS treatments, respectively. Dietary alpha-tocopherol supplementation (VIT E v. control) slightly increased milk fat content by 0.23 percentage units, but did not significantly alter milk fatty acid composition. Plasma trans-11 18:1 (VA) content tended to increase and trans-10 18:1 levels numerically declined following alpha-tocopherol supplementation suggesting possible changes in rumen biohydrogenation products. In addition, increased alpha-tocopherol intake in TMR-fed cows decreased serum urea levels and tended to alter milk fat 15:0 suggesting changes in rumen microbial populations. However, when compared with cows grazing pasture, TMR-fed cows supplemented with alpha-tocopherol, still produced milk with lower cis-9, trans-11 CLA and VA, and higher trans-10 18:1 concentrations suggesting alpha-tocopherol is not a primary reason for milk fatty acid profile differences between pasture and TMR-fed cows. Therefore, additional unknown pasture constituents favour production of fatty acids originating from the cis-9, trans-11 instead of the trans-10, cis-12 CLA biohydrogenation pathways.
authors.affiliation: Dexcel Ltd., Private Bag 3221, Hamilton, New Zealand.
authors.forename: Jane K
authors.initials: JK
authors.lastname: Kay
authors.forename: John R
authors.initials: JR
authors.lastname: Roche
authors.forename: Eric S
authors.initials: ES
authors.lastname: Kolver
authors.forename: Norman A
authors.initials: NA
authors.lastname: Thomson
authors.forename: Lance H
authors.initials: LH
authors.lastname: Baumgard
mesh_terms: D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle; D019587:Dietary Supplements; D005227:Fatty Acids / Q000032:analysis* / Q000097:blood*; D005260:Female; D007774:Lactation; D044243:Linoleic Acids, Conjugated / Q000032:analysis; D008055:Lipids / Q000032:analysis; D008892:Milk / Q000737:chemistry*; D013230:Stearoyl-CoA Desaturase / Q000378:metabolism; D024502:alpha-Tocopherol / Q000008:administration & dosage*
chemical_list: D005227:Fatty Acids; D044243:Linoleic Acids, Conjugated; D008055:Lipids; D013230:Stearoyl-CoA Desaturase; D024502:alpha-Tocopherol