Duodenal and Milk Trans Octadecenoic Acid and Conjugated Linoleic Acid (CLA) Isomers Indicate that Postabsorptive Synthesis Is the Predominant Source of cis-9-Containing CLA in Lactating Dairy Cows
2002
Piperova, Liliana S. | Sampugna, Joseph | Teter, Beverly B. | Kalscheur, Kenneth F. | Yurawecz, Martin P. | Ku, Youh | Morehouse, Kim M. | Erdman, Richard A.
Duodenal and milk samples obtained from lactating cows in a previous study were analyzed to compare the content and isomer distribution of conjugated linoleic acids (CLA) and trans-18:1 fatty acids (tFA). Four diets containing either low [25 g/100 g dry matter (DM)] or high (60 g/100 g DM) forage were fed with or without 2% added buffer to four multiparous Holstein dairy cows in a 2 × 2 factorial, 4 × 4 Latin square design with 3-wk experimental periods. Duodenal flows of CLA were low (1.02–1.84 g/d), compared with that of tFA (57–120 g/d), regardless of diet. The greatest amounts of CLA and tFA, as well as the greatest proportions of trans-10–18:1 (P < 0.02), and cis-9, trans-11 (P < 0.01) and trans-10, cis-12 CLA (P < 0.01) were in the duodenal flow of cows fed the low forage unbuffered diet. In milk fat, tFA were increased by the low forage unbuffered diet and the trans-10–18:1 (P < 0.02) replaced trans-11–18:1 as the major 18:1 isomer. Milk CLA secretion (7.2–9.1 g/d) was greater (P < 0.001) than that in the duodenal flow with each diet. This was due to the increase in cis-9, trans-11–18:2 and trans-7, cis-9 CLA, resulting most likely from endogenous synthesis via Δ9-desaturation of ruminally derived tFA. For other CLA isomers, duodenal flow was always greater than milk secretion, suggesting that they essentially were produced in the rumen.
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