Fig. 1. A, Mechanism of the action of porcine zona pellucida in mares. Normal and inhibition of sperm binding by anti-zona pellucida antibody.1 anti-GnRH antibody.1
B, Mechanism of action of gonadotropin-releasing hormone. Normal and inhibition of GnRH function by Adapted from Asa et al. (1996).26
sites on the zona pellucida of horse oocytes. When binding of sperm is inhibited, fertilization is pre- vented (Fig. 1A).35 Porcine zona pellucida-based vaccines have been
the most extensively studied contraception agent in free-ranging horse populations. Initial studies on
428 2014 Vol. 60 AAEP PROCEEDINGS
the successful use of pZP in wild horses was reported in the late 1980s, and progress in its development for optimal use in the management of free-ranging horses has been slow. There are currently three formulations of pZP-based vaccines used under ex- perimental conditions in an effort to find a suitable
