Background: A wide range of isomer-specific health benefits have been attributed to conjugated linoleic acids (CLAs). Little information is currently available on the influence of different feed components on the concentration of CLA isomers in ruminant-derived products. The aims of this study were to compare the effect of cereal mix or dried sugar beet pulp supplementations fed to grazing dairy cows on milk CLA isomeric distribution and to examine the monthly variation of CLA isomers during the grazing season.
Results: The concentrations of the isomers t7c9, t10c12 and t10t12 were higher in milk from cows supplemented with cereals (P < or = 0.001). The milk of beet pulp-supplemented cows showed higher levels of the isomers t11c13 (P < or = 0.05), t9t11 (P < or = 0.001) and t7t9 (P < or = 0.01). Total CLA as well as seven other minor isomers were not significantly affected by the concentrate type. Monthly variations occurred extensively for almost all detected isomers. Total CLAs showed the highest values at the beginning of the grazing season and in autumn in coincidence with plant regrowth.
Conclusion: These results show that even at low levels, supplement types can significantly influence the concentration of some CLA isomers in milk fat; an indication is given of the possibility to manipulate the animals' diet to change the CLA isomeric profile in ruminant-derived products.