Incomplete nuclear reprogramming remains a major limitation in somatic cell nuclear transfer (SCNT), often due to persistent epigenetic marks such as aberrant DNA methylation patterns that impair gene expression and compromise embryonic viability. In this context, highly plastic cells such as mesenchymal stem cells (MSCs) have emerged as promising nuclear donor candidates for improving cloning outcomes in horses [1]. This study compared the efficacy of bone marrow-derived mesenchymal stem cells (BM-MSCs) and adult dermal fibroblasts (ADF) as nuclear donors in equine SCNT. Embryonic development in vitro and reproductive success in vivo were evaluated. A total of 1,138 equine oocytes were collected via ovum pick-up (OPU) [2] over 60 sessions (703 for BM-MSCs; 435 for ADF). Day 7 blastocysts were produced by conventional SCNT procedures [2] and transferred individually to recipient mares at Day 4 post-ovulation (96 for BM-MSCs; 42 for ADF). No significant differences were observed in the blastocyst formation rates (BM-MSCs: 33.65% vs ADF: 28.55%), Day 14 pregnancy rates (BM-MSCs: 55.21% [53/96] vs ADF: 57.14% [24/42]) or subsequent foaling rates (BM-MSCs: 41.50% vs ADF: 50.00%). Remarkably, 100% (22/22) of the foals from BM-MSC-derived embryos were born normal and healthy, whereas 75% (9/12) of those from ADF-derived embryos were viable (P<0.05). Furthermore, several surviving foals from the ADF group exhibited neonatal abnormalities, including minor limb deformities and umbilical enlargement, which required veterinary intervention. In conclusion, the use of BM-MSCs as nuclear donors resulted in better foaling outcomes and fewer postnatal complications, supporting their application as the preferred alternative to somatic fibroblasts in equine SCNT programs.