Awassi breed is an important sheep in the Middle East, but its lower twinning potential is a limitation against improvement. Due to the dynamic role of oocyte-expressed protein (OOEP) gene in controlling folliculogenesis, this study was conducted to evaluate the possible association between OOEP and twinning rate, as well as body measurement traits, in Awassi ewes. A total of 232 Awassi ewes (123 ewes-producing singletons and 109 ewes-producing twins) were included in this study. Three PCR fragments (OOEP-1 to OOEP-3) were designed to cover the majority of OOEP sequences and genotyped by single-strand conformation polymorphism (SSCP) method. One nucleic acid variant was identified in the intron-2 of OOEP-3, or rs430263839:A>G. Ewes with rs430263839:AG genotype showed variable significant values of larger head length, chest and abdominal circumferences, and higher prolificacy and twinning rates than ewes with the rs430263839:AA genotype. The conducted computations predicted that the detected SNP had caused altered splicing mechanisms in ewes with rs430263839:AG genotype. The increased abdominal and chest diameters in ewes with the rs430263839:AG genotype were thought to help the uterus accommodate more lambs. The predicted splicing alteration caused by this SNP is the putative mechanism by which these ewes may improve reproductive and productive traits. This is the first study that demonstrated the importance of OOEP as a potential biomarker for the twinning rate, prolificacy, and some body measurement traits in Awassi ewes with an opportunity to be introgressed to other breeds using large-scale association analysis.

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