This study about the forage fatty acid composition of forages in Argentina clearly shows the significant changes in total lipids and fatty acid composition, particularly in the contribution of 18:2n-6 and 18:3n-3, the ratio 18:3n-3/18:2n-6 and the total PUFA due to cultivar, cutting date and season. Considering the importance of these fatty acids as substrates for CLA and n-3 PUFA concentrations in beef, the fatty acid composition of forages needs to be considered in forage grazing beef production systems. There is also a need for more understanding of processes that occur in the rumen. There are factors other than the fatty acids influencing the amounts of PUFA that escape from the rumen and these factors warrant further study. It is important to know the degree of variation in both total lipids and individual fatty acids in forages with a view to establishing the potential to cultivate grasses for a higher content of n-3 PUFA and hence the opportunity to deliver more n-3 PUFA into beef.