OGP, encoded by the gene, is the major non-serum oviductal protein in most mammals. In the genome of , has been identified as a pseudogene. However, presents a functional gene. As the rat and the mouse belong to the subfamily Murinae, has probably been lost after their divergence. This study aims to determine when the pseudogenization event occurred and which proteins could replace its function. To attain that, the potential expression of members belonging to the GH18 family is investigated in the rat oviduct by means of molecular and proteomic analyses. Specific regions are sequenced in different murine rodent species. The analysis reveals the presence of stop codons only in some species of the Rattini tribe, suggesting that the majority of the murine species present a functional gene. Thus, the pseudogenization of could be dated back to around 10 Mya, after the divergence of the Rattini tribe. The expression of several genes and proteins of the GH18 family, such as , , , and , are detected in the rat oviduct. This study opens the door for further research on GH18 family proteins that mimic the OGP functions in species where is pseudogenized.