Endogenous synthesis and enhancement of conjugated linoleic acid
in pasture-fed dairy cows
J.K. KAY, T.R. MACKLE, M.J. AULDIST, N.A. THOMSON AND D.E.
BAUMAN
Dexcel, Private Bag 3221, Hamilton, New Zealand.
E-Mail:
NZSAP 2002 Abstract No. 4
Proceedings of the New Zealand Society of Animal Production 62:
7-11
The primary conjugated linoleic acid (CLA) isomer in milkfat,
cis-9, trans-11 CLA, is a proven anticarcinogen in rodents
and can be derived directly from ruminal biohydrogenation of linoleic
acid. The major fatty acid in pasture, however, is alpha-linolenic acid;
the biohydrogenation of which does not produce cis-9,
trans-11 CLA as an intermediate. Therefore, in grazing cows,
cis-9, trans-11 CLA must be produced by other sources,
possibly via delta 9-desaturation of trans-11 vaccenic acid (TVA), a
biohydrogenation product of both alpha-linolenic acid and linoleic acid.
Studies were conducted to i) determine the importance of endogenous
synthesis of cis-9, trans-11 CLA in pasture-fed cows and
ii) increase the level of cis-9, trans-11 CLA. The first
study involved abomasal infusion of sterculic oil (SO) to inhibit the
activity of the delta 9-desaturase enzyme. Abomasal infusion of SO
decreased the concentration of cis-9, trans-11 CLA in milk
fat by 71% (P<0.01; 3.6 c.f. 12.1 ± 0.15 mg/g fatty acid). The
presence of cis-9, C 1 0:1, cis-9,
C12:1 and cis-9, C14:1 in the milk fat of
cows following SO treatment indicated delta 9-desaturase was not
completely inhibited. Using the changes in these fatty acids to evaluate
the extent of delta9-desaturase inhibition with SO treatment, an
estimated 87-100% of cis-9, trans-11 CLA in milk fat was
of endogenous origin. In the second study, sunflower oil at 4%
DMI/cow/day invoked a 38% increase (P<0.01) in milk fat TVA (61.3
c.f. 44.4 ± 0.51 mg/g fatty acid) and a subsequent 28% increase
(P<0.01) in cis-9, trans-11 CLA concentrations compared to
control (28.5 c.f. 22.3 ± 0.19 mg/g fatty acid). Results
demonstrate that endogenous synthesis is the major source of cis-9,
trans-11 CLA in pasture-fed dairy cows and levels can be enhanced by
increasing the supply of the ruminally-derived precursor, TVA.
Keywords: NZSAPAB;
conjugated linoleic acid; trans-11 vaccenic acid;
delta 9-desaturase; milkfat; pasture
Last Updated 30/07/2002
