Daldaban, F.Karakus, F.Arslan, K.Cinar, M.U.Akyuz, B.2025-06-012025-06-0120252053-109510.1002/vms3.703952-s2.0-105005768481https://doi.org/10.1002/vms3.70395Farm animals’ birth weight and postnatal live weight gain (LWG) are essential for offspring survival and meat yield. This study investigated the relationship between DGAT1-AluI and CAST-MspI polymorphisms, DGAT1-AluI and CAST-MspI genotypic interaction and LWG in Morkaraman lambs. A total of 514 Morkaraman lambs were genotyped for DGAT1-AluI and CAST-MspI polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) methods. The TT genotype in the DGAT1-AluI polymorphism consistently exhibited higher birth weight and weights at 30th, 60th and 90th days compared to the other genotypes. At the MM genotype, CAST-MspI showed an association between the 30th and 60th and weaning weights. In this study, we found that the M allele for the CAST-MspI polymorphism positively influenced growth performance in sheep. However, the TT genotype in the DGAT1-AluI was associated with even better growth performance. On the other hand, we determined for the first time that the TTMN genotype interaction in the DGAT1 × CAST genes serves as a robust genetic marker for weight gain at birth and on the 30th, 60th and 90th days. In conclusion, it is suggested that the DGAT1 × CAST gene TTMN genotype interaction, identified for the first time in this study, may serve as a novel and effective marker for body weight gain in the Morkaraman sheep breed. © 2025 The Author(s). Veterinary Medicine and Science published by John Wiley & Sons Ltd.eninfo:eu-repo/semantics/closedAccessCast × Dgat1 InteractionGenetic MarkerPolymorphismSheepWeight GainArticle113Q2Q140384228WOS:001490950000001