A commonly used rumen-protected conjugated linoleic acid supplement marginally affects fatty acid distribution of body tissues and gene expression of mammary gland in heifers during early lactation

Background: Conjugated linoleic acids (CLA) in general, and in
particular the trans-10, cis-12 (t10, c12-CLA) isomer are potent
modulators of milk fat synthesis in dairy cows. Studies in rodents,
such as mice, have revealed that t10, c12-CLA is responsible for
hepatic lipodystrophy and decreased adipose tissue with subsequent
changes in the fatty acid distribution. The present study aimed to
investigate the fatty acid distribution of lipids in several body
tissues compared to their distribution in milk fat in early
lactating cows in response to CLA treatment. Effects in mammary
gland are further analyzed at gene expression level. Methods:
Twenty-five Holstein heifers were fed a diet supplemented with (CLA
groups) or without (CON groups) a rumen-protected CLA supplement
that provided 6 g/d of c9, t11-and t10, c12-CLA. Five groups of
randomly assigned cows were analyzed according to experimental
design based on feeding and time of slaughter. Cows in the first
group received no CLA supplement and were slaughtered one day
postpartum (CON0). Milk samples were taken from the remaining cows
in CON and CLA groups until slaughter at 42 (period 1) and 105
(period 2) days in milk (DIM). Immediately after slaughter, tissue
samples from liver, retroperitoneal fat, mammary gland and M.
longissimus (13th rib) were obtained and analyzed for fatty acid
distribution. Relevant genes involved in lipid metabolism of the
mammary gland were analyzed using a custom-made microarray
platform. Results: Both supplemented CLA isomers increased
significantly in milk fat. Furthermore, preformed fatty acids
increased at the expense of de novo-synthesized fatty acids. Total
and single trans-octadecenoic acids (e. g., t10-18:1 and t11-18:1)
also significantly increased. Fatty acid distribution of the
mammary gland showed similar changes to those in milk fat, due
mainly to residual milk but without affecting gene expression.
Liver fatty acids were not altered except for trans-octadecenoic
acids, which were increased. Adipose tissue and M. longissimus were
only marginally affected by CLA supplementation. Conclusions: Daily
supplementation with CLA led to typical alterations usually
observed in milk fat depression (reduction of de novo-synthesized
fatty acids) but only marginally affected tissue lipids. Gene
expression of the mammary gland was not influenced by CLA
supplementation.