Organic systems are highly dependent on the environment and require animals well adapted to local conditions. In Spain, organic dairy farmers are not satisfied with the productive performance of their herds and ask for technical advice to obtain suitable animals for organic systems. The milk productive performance (milk yield, nutritional composition, and somatic cell count) of Holstein-Friesian cows in organic farming in North Spain compared with conventional farms has been analysed. When

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... diversity was present in the same organic farm, Holstein-Friesian milk performance was compared with other breeds and/or crosses. Holstein-Friesian cows in organic farming produce slightly less milk than grazing conventional cows, but milk was similar in composition and somatic cell count across systems. The limited data from organic farms where breed diversity exists indicate that Holstein-Friesian cows produce numerically more milk than other breeds and crosses but with statistically lower protein content. Considering that in Spain organic milk production is mostly used for liquid milk consumption and that the payment system is based only on milk volume, Holstein-Friesian cows would better fit the farmer interests than other breeds or crosses. However, in addition to productive performance, reproductive efficiency, animal health and consumer's preferences should be fully considered when selecting a breed for organic production. If Holstein-Friesian was the selected breed, efforts should be made to identify cows within the breed that are best adapted to organic conditions. New productive, reproductive, nutritional and economic studies would be needed to develop a genetic merit index for organic systems.