Prostaglandins Are Commonly Used to Terminate Pregnancies in Many Domestic $\alpha$

Prostaglandins are commonly used to terminate pregnancies in many domestic species. Injection of the specific prostaglandin F_{2 $\alpha$} (PgF_{2 $\alpha$} ) is alone not 100% effective in causing parturition in cattle that are near term. Why?

A) PgF_{2 $\alpha$} is a prostaglandin that functions as a gastroprotectant
B) PgF_{2 $\alpha$} is not labeled for use in food animals
C) PgF_{2 $\alpha$} doesn't exert an influence on the uterus
D) PgF_{2 $\alpha$} doesn't exert an influence on the corpus luteum