Binds to oocyte zona pellucida in vivo. May play a role in the fertilization process and/or early embryonic development. Secretory granules. Oviduct. Levels are highest in the fimbria and ampulla at estrus and on day 1 of pregnancy, when gamete transport and fertilization occurs in the E2-dominated fallopian tube. Levels decline significantly on day 2 and undergo a further significant reduction on day 3 of pregnancy coincident with transport of the embryo from the oviduct to the uterus, a reproductive stage associated with rising progesterone levels. Belongs to the glycosyl hydrolase 18 family.