Inhibition of ∆9-desaturase activity with sterculic acid: effect on the endogenous synthesis of cis-9 18:1 and cis-9, trans-11 18:2 in dairy sheep.

ABSTRACT

This study was conducted in lactating ewes to examine the involvement of ∆(9)-desaturase in mammary lipogenesis, especially in the endogenous synthesis of cis-9, trans-11 182 and cis-9 181, because no information on this matter was available for dairy sheep. With this aim, 6 Assaf ewes were monitored in a 15-d experiment, which included a 5-d pretreatment period, a 5-d treatment period, and a 5-d posttreatment period. During the treatment period, ewes received 0.5 g/d of sterculic acid (a cyclopropene fatty acid that inhibits ∆(9)-desaturase), delivered intravenously in 4 equal doses at 6-h intervals. Animals were fed pasture to supply mainly α-linolenic acid and minimize the amount of milk cis-9, trans-11 182 of ruminal origin. Sterculic acid administration was calculated to inhibit ∆(9)-desaturase by 70% based on the milk content of cis-9 141. This inhibition resulted in decreases in the milk content of the enzyme products (e.g., cis-9 101, cis-9 141, cis-9 161, cis-9 181, and cis-9, trans-11 182) and increases in its substrates (e.g., 140, 180, and trans-11 181), as well as in reductions in the desaturase indexes. Some other milk fatty acids, further to previously reported products or substrates of ∆(9)-desaturase (e.g., cis-15 181 and cis-9, cis-15 182, or trans-11, trans-15 182, and cis-9, trans-11, trans-15 183), were also affected by sterculic acid administration. Endogenous synthesis was the major source of cis-9 181 and cis-9, trans-11 182, accounting for 63 and 74% of its content in milk fat, respectively. To our knowledge, the present study provides the first estimates of endogenous synthesis of these 2 bioactive fatty acids in ovine milk fat.