miRNAs regulate the expression of target genes in diverse cellular processes and hence play important roles in physiological processes including developmental timing, patterning, embryogenesis, organogenesis, cell lineage, myogenesis and growth control. A comparative expression analysis of miRNAs expressed in the longissimus dorsi muscle at two prenatal stages (63 and 91 days post-conception (dpc)), and one adult stage (180 days post-natum) in both German Landrace (DL) and Pietrain (Pi) pig breeds was performed using a custom-designed array. During the prenatal stages, miR-199 and the miR-17 families were significantly up-regulated at 63 dpc, whereas miR-1 and miR-133a were overexpressed at 91 dpc. The abundance of several miRNAs was increased in the adult stage compared to 91 dpc including miR-1, miR-133, miR-22(a/b) and miR-29a. Some miRNAs were breed-specific, such as miR-199 and the miR-17 families which were all up-regulated in Pi pigs, while miR-133, miR-181 and miR-214 were up-regulated in DL pigs. Several pathways related to muscle development were enriched with predicted targets for the differentially expressed miRNAs. The dynamic expression and breed-associated regulation of porcine muscle miRNAs suggests a functional role for miRNA-mediated gene regulation during muscle development and phenotypic variations of muscle traits. (C) 2015 Elsevier B.V. All rights reserved.