Development of fore stomach fermentation in ruminants is associated with the formation of a wide range of positional and geometric isomers of conjugated linoleic acid (CLA) synthesized during ruminal biohydrogenation of dietary 18:2n-6 and 18:3n-3. More than 15 individual isomers of CLA have been detected in digesta at the omasum or duodenum with the amounts available for absorption being highly dependent on diet composition. Little is known about the metabolic fate and physiological activity of most CLA isomers in the host ruminant. However, ruminant tissues contain a wide range of CLA isomers indicating that these serve as substrates for essential functions including phospholipid synthesis. Virtually all of the evidence pertaining to the biological activity of CLA in cattle is based on post-ruminal infusions or feeding studies examining the effects of synthetic sources enriched in cis-9, trans-11 and trans-10, cis-12. Dietary supplements of rumen protected synthetic CLA (PR-CLA) decrease milk fat content in lactating cows, changes that are often accompanied by an increase in milk and milk protein yield and/or improved energy status. Effects of RP-CLA on lactational performance may, at least in part, to be mediated via the repartitioning of energy towards body tissues in the absence of changes in heat production or diet digestibility. Available data highlight a role of CLA in minimizing excessive mobilization of body tissues during periods of energy insufficiency in the dairy cow.

Isomers of conjugated linoleic acid as important nutrients in the dairy cow

244th National Meeting (2012)

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