RNA interference (RNAi) is a recent, gene silencing technique. It could be valuable in studying gene function and producing economically beneficial phenotypes in livestock. RNAi was tested in fetal porcine fibroblast cells by attempting to silence endogenous myostatin. Loss-of-function of myostatin leads to 20% increase in lean meat in double-muscled breeds of cattle. Five anti-myostatin shRNAs were introduced into cells. Four led to highly efficient silencing (up to 97%) of myostatin mRNA, however all induced interferon-responsive gene expression (OAS1 and IFN-[beta]). Interferon induction was generated by any plasmid and not related to shRNA expression or myostatin silencing. Methylating CG motifs in the plasmid appear to decrease the level of interferon induction but not to baseline levels. These results demonstrate highly efficient RNAi in porcine cells, however further work must be performed to decrease interferon induction. With anticipation, a double-muscled phenotype can be generated in RNAi-transgenic pigs, which can become a commercially valuable breed and be used as a large animal model for studying muscle development and myogenesis regulatory network.