Manipulation of Conjugated Linoleic Acid in Milk and Meat through Dietary Management in Ruminant Animals: A Review

Abstract

Importance of conjugated linoleic acid (CLA) in the diets of humans as a vital health promoter has gained significance in recent times. CLA is a collective term used for a mixture of positional and geometrical (cis or trans) isomers of linoleic acid with conjugated double bonds. The major isomers are c9t11 and t10c12 besides many others. Most prevalent and biologically active CLA isomer is c9t11. Amongst, several beneficial health effects inhibition of cancer, coronary heart diseases and mutagenesis are most important aspects, besides reduction of body fat in humans. Even though, ruminant milk and meat and their products are richest sources of CLA, further enrichment of these products is required to obtain the health benefits of CLA in human population. This can be achieved by increase of CLA contents of above livestock products by way of various dietary manipulations in the ruminant animal production system. CLA is principally synthesized in the rumen by biohydrogenation of linoleic acid and endogenous desaturation of trans vaccenic acid (TVA), which is also produced in the rumen. Feeding ruminant animals with diets either rich in linoleic acid or poor but effectively increase the TVA production is the practical way for elevation of CLA contents in milk and meat. Grazing on pastures rich in grasses enhanced the milk and meat CLA contents. Supplementing ruminant diets with oilseeds/oils viz. soybean, rapeseed, linseed, sunflower, safflower etc. or fish meal/oil and some methods of feed processing like- cracking, rolling, roasting, extrusion etc. increased milk and meat CLA contents. Literature relates that high level of concentrate feeding did not support elevation of CLA, whereas feeding good quality roughage was always beneficial. Moreover use of ionophore antibiotics in the animal diet produced marginal increase; their role is limited due to prohibition. The effects of various other dietary factors and processing methods for increasing CLA levels in the ruminant livestock products have been discussed. Future research studies on aspects of synchronized ruminal fermentation along with effective biohydrogenation and optimization of passage rates are suggested. The role of alternate hydrogen sink in rumen such as organic acids, component of Krebs cycle may also be explored for potential of increasing CLA levels.