Relationship between the Composition of Lipids in Forages and the Concentration of Conjugated Linoleic Acid in Cow’s Milk: A Review

SIMPLE SUMMARY: Conjugated linoleic acid (CLA) has been shown to have protective effects against various common diseases, such as obesity and cancer, improving human health. For several years, efforts have been made to increase CLA levels in milk by including sources of fats and oilseeds in the diets of lactating cows, causing a decrease in the amount of fat in the milk itself and a decrease in the yield of the products derived from it. A “safe” and economical way to increase CLA content without affecting fat content, is through grazing feeding since the content of CLA precursors (linoleic and α-linolenic acids) are present in greater quantity in pastures compared to feeding only balanced diets. The content of these precursors will depend on factors, such as age and nitrogen fertilization, since the high availability of nitrogen stimulates the synthesis of metabolic components, such as leaf protein. The bibliographic review shows how the inclusion of different forages and the agronomic management of pastures promote the improvement of CLA levels in milk, giving “an added value”. ABSTRACT: Conjugated linoleic acid (CLA), has been shown to have protective effects against various diseases, such as obesity, arteriosclerosis, diabetes, chronic inflammatory diseases, and cancer. This fatty acid in ruminants results from two processes, biohydrogenation, which takes place in the rumen, and de novo synthesis, carried out in the mammary gland, and it has linoleic and α-linolenic acids as its precursors. The amounts of precursors in the diets of animals are related to the amounts of CLA in milk. In the literature review, it was found that the milk of cows fed fresh forage has a higher amount of CLA because they have a higher amount of linoleic acid and α-linolenic acid compared to other foods used in the diets of cows. The amount of CLA precursors in pastures can be increased through agronomic practices, such as nitrogen fertilization, and regrowth age. It is also a technique used to increase the amount of CLA in milk to obtain a greater benefit regarding its nutritional value.