Comparative effects of GnRH and porcine zona pellucida (PZP) immunocontraceptive vaccines for controlling reproduction in white-tailed deer (Odocoileus virginianus).

Fawning rates and mating behaviour were compared between white-tailed deer (Odocoileus virginianus) treated with GnRH and porcine zona pellucida (PZP) immunocontraceptive vaccines from 1997 to 2000. Female deer from a herd of 102 deer at Seneca Army Depot, near Romulus, New York, were treated with prime and booster injections of PZP (n = 22) or GnRH vaccine (n = 32), or remained untreated as controls (n = 34). During the summers after booster treatment, observed fawning rates for adult female deer were similar for both PZP-treated (0.10-0.11 fawns per female) and GnRH-treated (0.13-0.22 fawns per female) female deer, and were significantly lower (t = -8.93 and t = -9.73; P < or = 0.0005, respectively) than those observed for control female deer (1.22-1.38 fawns per female). During the second (0.36 fawns per female) and third summers (0.61 fawns per female) after the last booster injection, GnRH-treated female deer still produced significantly fewer fawns than did the controls (1.38 and 1.31 fawns per female, respectively). In one breeding season after treatment, five of 18 (28%) females vaccinated with PZP produced fawns, similar to the rate for GnRH-treated females (29%). In addition, females treated with GnRH had fewer oestrous cycles per female (0.06, P < or = 0.05) than did either control (0.22 cycles per female) or PZP-treated deer (0.36 cycles per female). Initial PZP treatment followed by a booster dose 5-7 months later reduced fawn production and prolonged the breeding season as females repeatedly returned to oestrus, similar to results reported in other studies.