Using an array consisting of 10665 70-mer oligonucleotide probes, the longissimus dorsi muscle tissue expression during growth in nine pigs belonging to Casertana (CT), an autochthonous breed characterized by slow growth and a massive accumulation of backfat, was compared with that of two cosmopolitan breeds, Large White (LW) and a crossbreed (CB; Duroc×Landrace×Large White). The results were validated by real-time PCR. All animals were of the same age and were raised under the same environmental conditions. Muscle tissues were collected at 3, 6, 9 and 11months of age, and a total of 173 genes showed significant differential expression between CT and the cosmopolitan genetic types at 3months of age. Time series cluster analysis indicated that the CT breed had a different pattern of gene expression compared with that of the LW and the CB. Four of the eight clusters highlighted the gene differences between CT and the other two breeds, which were further supported by statistical analyses: clusters 4 and 5 contained a total of 71 genes that were underexpressed at 3months of age, and cluster 3 and cluster 7 included 28 and 42 genes respectively that were overexpressed at 3months of age. As expected, differentially expressed genes belonged to the category of genes coding for contractile fibres and transcription factors involved in muscle development and differentiation. These findings highlight muscle expression genes during pig growth and are useful to understand the genetic meaning of the different developmental rates
