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- 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.
- Authors
Jane K Kay; John R Roche; Eric S Kolver; Norman A Thomson; Lance H Baumgard
- 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 (α-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 10000 i.u. α-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 α-tocopherol intakes were approximately 468, 10520 and 1590 i.u./cow for the control, VIT E and PAS treatments, respectively. Dietary α-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 α-tocopherol supplementation suggesting possible changes in rumen biohydrogenation products. In addition, increased α-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 α-tocopherol, still produced milk with lower cis-9, trans-11 CLA and VA, and higher trans-10 18∶1 concentrations suggesting α-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.
- Publication
Journal of Dairy Research, 2005, Vol 72, Issue 3, p322
- ISSN
0022-0299
- Publication type
Article
- DOI
10.1017/s0022029905000944