A microarray is an orderly arrangement of spots printed on an impermeable solid support, usually glass, silicon chips or nylon membrane. Each gene is represented by multiple spots and a single microarray chip can detect thousands of expressed genes simultaneously and in some cases the entire genome of an organism. Microarrays therefore allow high-throughput determination of changes in expression of thousands of genes of both known and unknown function in response to experimental treatment and so aids in the identification of novel genes associated with physiological pathways. For most mammalian species there is currently either a lack of a specific microarray or a limited coverage of the genome, both of which limit the use of microarrays in those species. For humans and rodents, however, there is complete coverage of the expressed genome. The aim of this study was therefore to determine whether the human Affymetrix GeneChip could be used to measure gene expression in a ruminant species and whether this is a viable alternative to species specific microarrays.