Predicting Delta9-desaturase activity and the association with
conjugated linoleic acid (CLA) concentration in bovine milk
N.A. THOMSON, A. CHAND AND J.K. KAY
Dexcel, Private Bag 3221, Hamilton, Fax: 07 858 3879
E-Mail:
NZSAP 2003 Abstract No. 8
Proceedings of the New Zealand Society of Animal Production
63: 25-30
The major source of cis-9, trans-11 conjugated
linoleic acid (CLA) in bovine milk is from the post-ruminal conversion
of trans-11 C18:1 (TVA) by delta9-desaturase.
Activity of delta9-desaturase is predicted from the
product/substrate ratios of fatty acids dependant on the enzyme. Data
from three experiments was investigated. Cows selected for having soft
or hard milk fat were fed ruminally protected oilseed in spring 1999,
and autumn 2000 or crushed full-fat rapeseed in autumn 2001. Cows with
harder milk fat had higher concentration of milk fat (P<0.001), and
lower concentrations (P<0.001) of TVA and CLA. Feeding ruminally
protected oilseed in spring had no effect on milk fat, TVA or CLA
concentrations but in autumn increased (P<0.001) milk fat
concentration. Feeding crushed rapeseed depressed (P<0.001) TVA and
CLA concentrations. Ratios of fatty acid pairs dependent on
delta9-desaturase (C10:1/C10:0,
C16:1/C16:0 cis-9 C18:1/C 18:0
and CLA/TVA) were lower in milk from cows with harder milk fat and the
C12:1/C12:0, C14:1/C14:0 ratios were similar for soft and
hard milk fat cows. Feeding ruminally protected oilseed decreased
(P<0.001) all ratios except for C12:1/C12:0 in
autumn 2000. Feeding rapeseed had no effect on the product/substraight
ratios except the cis-9 C18:1/C18:0 ratio.
None of these ratios were associated with milk fat CLA concentrations in
spring however in autumn C14:1/C14:0 and
C16:1/C16:0 were positively associated
(P<0.05). Significant associations (P<0.001) between the milk fat
cis-delta9 C18:1/C18:0 ratio and
CLA concentration and between TVA and CLA concentrations were also
evident. This suggests that milk fat CLA concentrations may be
influenced more by the availability of TVA than by the variation in the
activity of delta9-desaturase.
Keywords: NZSAPAB;
bovine milk fat; delta9-desaturase; conjugated
linoleic acid (CLA); product/substrate ratios
Last Updated 8/07/2004
