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The results of a 6-year behavioral study of white-tailed deer (Odocoileus Virginianus) treated with two immunocontraceptive vaccines, porcine zona pellucida (PZP) and gonadotropin releasing hormone (GnRH) are summarized. Does were immunized late summer and early fall. In November, does were exposed to bucks and observations were made 2-3 times daily for one half hour through the end of February. Does were considered to be in estrus when they were the object of intensive sexual interest by the buck. Compared to controls, PZP-treated does had a significantly lower fawning rate and an increase in the average number of estrous cycles observed per doe. The average breeding days each year for the control group was 45, whereas in some years some PZP treated does were breeding more than 150 days. When previously treated PZP does were not treated in subsequent years, antibody titers declined and fertility was gradually restored. GnRH immunization also induced a decrease in fawning rate, although the average estrous cycles observed per doe were comparable to averages observed for control animals. There was no indication that the GnRH treatment caused repeated estrous cycling as with the PZP treated does. Based on limited observations GnRH treatment has a negative impact on males, resulting in immunological castration, compromised libido and abnormal antler development.