CLA and Lipid Metabolism

Investigations in which the transfer of CLA to milk fat in dairy cows was examined showed that supplementation of mixed isomers of CLA resulted in a dramatic reduction in milk fat secretion (Loor and Herbein, 1998 Chouinard et al., 1999a, b). Decreases of up to 50% in milk fat yield occurred and the effects were reversed when supplementation was terminated. Furthermore, effects were specific for milk fat with the yield of milk and other milk components being relatively unaffected. Initial investigations were of short duration ( 7 days) and the CLA supplement was infused abomasally as a convenient experimental method to avoid possible alterations during rumen fermentation. However, subsequent long-term studies (20 weeks) demonstrated that the reduction in milk fat synthesis was 

Initial studies on CLA showed that the reduction in milk fat secretion reflected decreases in fatty acid levels of all chain-length, but effects were most pronounced for those synthesized de novo (Loor and Herbein, 1998 Chouinard et al., 1999a,b). As investigations focused on trans-10, cis-12 CLA and expanded to include a range of doses, it was discovered that at lower doses, the reduction in milk fat was distributed more uniformly among the fatty acids synthesized de novo (short-chain and medium-chain length) 

Diet-induced MFD has been the subject of extensive research, especially over the last 50 years (see reviews by Davis and Brown, 1970 Palm-quist et al., 1993 Bauman and Griinari, 2001). Many theories have been advanced to explain diet-induced MFD, however, most have been found inadequate to explain the cause and mechanism of this phenomenon (Dor-eau et al., 1997a Bauman and Griinari, 2001, 2003). A shift in rumen fermentation is clearly involved and the occurrence corresponds to a marked increase in the trans 18 1 content of milk fat (Davis et al., 1970 Griinari et al., 1998). While VA is generally the principal trans 18 1 isomer in milk fat, a key development was the discovery by Griinari et al. (1998) that the change 

Recent investigations of the mechanism of diet-induced MFD indicate that it involves a coordinated reduction in the abundance of mRNA for key 

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