Dietary intake of omega-3 polyunsaturated fatty acids (n-3 PUFA) and conjugated linoleic acid (CLA) has been recognized as having potential positive effects on human health (Lock and Bauman, 2004). Furthermore, alteration of the fatty acid (FA) composition of milk through targeted manipulation of dairy cow diets can be achieved (Dewhurst et al., 2006). Although breed effects on the FA composition of milk have previously been reported (Kelsey et al., 2003), most work to-date has been conducted under high input TMR based systems. Furthermore, little is known on the effects of heterosis on concentrations of FA in milk. The objective of this study was to examine whether differences in milk FA concentration exist between two contrasting breeds of dairy cow and their F1 hybrid managed under a grazing based production system.