Trans-10, Trans-12 Conjugated Linoleic Acid Does Not Affect Milk Fat Yield but Reduces Δ~9-Desaturase Index in Dairy Cows

摘要

Trans-10, cis-12 conjugated linoleic acid (CLA) is a potent inhibitor of milk fat synthesis, and the magnitude of milk fat depression is often correlated with the fat content of this isomer. However, the trans-10, cis-12 CLA content does not always correspond to the extent of milk fat depression, and in some instances, an increase in the milk fat content of trans-10, trans-12 CLA has been observed. We synthesized trans-10, trans-12 CLA (> 90% purity) and investigated its effect on milk fat synthesis and incorporation into plasma lipids. Three rumen-fis-tulated Holstein cows were randomly assigned in a 3 x 3 Latin square experiment. Treatments were a 4-d abomasal infusion of 1) ethanol (control), 2) a trans-10, cis-12 CLA supplement (positive control), and 3) a trans-10, trans-12 CLA supplement; 5 g/d of the CLA isomer of interest was provided. Milk yield, dry matter intake, and milk protein were unaffected by treatment. Treatment with trans-10, trans-12 CLA had no effect on milk fat yield, whereas treatment with trans-10, cis-12 CLA reduced milk fat yield by 28%. Incorporation of CLA was greatest for the plasma triglyceride fraction, and the milk fat content was subsequently elevated within the respective treatment groups. The milk fatty acid composition indicated that Δ~9-desaturase was reduced significantly for both CLA treatments, but the reduction was greater for the treatment with trans-10, trans-12 CLA. Overall, abomasal infusion of trans-10, trans-12 CLA and trans-10, cis-12 CLA altered the desaturase ratios, but only trans-10, cis-12 CLA reduced milk fat synthesis.