The Importance of Reversal Data in Making Contraception Recommendations
American Association of Zoo Veterinarians Conference 2013
Mary Agnew, PhD; Cheryl Asa, PhD
AZA Wildlife Contraception Center, Saint Louis Zoo, Saint Louis, MO, USA


The mission of the AZA Wildlife Contraception Center (WCC) is to provide information and recommendations about contraceptive products that are safe, effective, and reversible. The WCC relies on feedback from the zoo community to integrate these three mission pillars into frequently updated recommendations. While communication about safety and efficacy between the WCC and zoo professionals has always been strong, collecting reversal data has proven a challenge. The lack of reversal data has grown especially concerning in recent years due to the long suppression times associated with deslorelin (Suprelorin®, Virbac Animal Health, Carros cedex, France) use. Animals treated with Suprelorin® are often suppressed much longer than the minimum durations of effect suggested by the implant manufacturer. Consequently, timing breeding recommendations has grown increasingly difficult as some individuals do not reproduce for many years after treatment or may even remain permanently suppressed.

There are several challenges associated with collecting reversal data, challenges that make calculating times to reversal extremely complicated. At the most basic level is the question of whether an individual ever had an opportunity to breed after treatment. Without feedback from the housing institution, it is impossible to categorize an animal as one that never returned to cycling or one that simply was treated and was never given mate access. Another challenge is a byproduct of the nature of master planning, which frequently involves transferring individuals for breeding. Once an animal leaves the institution that administered contraception, the institution is no longer responsible for providing updates on that animal. Similarly, the receiving institution may not provide reversal data to the WCC since the animal was contracepted at a different location. Thus, critically important reversal data fall through the cracks. Another scenario that leads to loss of reversal data occurs when an animal is treated with contraception and then has a planned or unplanned pregnancy many years later. Because the contraceptive was not administered recently, the reversal data may not be reported to the WCC.

Since lions have been treated with Suprelorin® more than most other species, the WCC formed a formal relationship with the AZA Lion SSP to develop a model for improving the efficiency of reversal data collection. Thanks to excellent institutional feedback and support from the AZA Lion SSP Coordinator, we know more about reproductive recovery in lions than in any other species. Evidence is accumulating that the pituitary hormone that stimulates follicle growth (FSH) and estrogen production (which can stimulate estrous behavior) may recover before the hormone necessary for ovulation (LH). And, with seven recorded reversals to date, the average time from implant placement to conception can be calculated. For all African lions given the 9.4-mg Suprelorin® formulation (n=57), four lions reversed, conceiving between 2.3 and 3.6 yr later. For all lions treated with the 4.7-mg formulation (n=17), two lions gave birth, conceiving 4.4 and 3.5 yr after implant placement. One of these females had an extensive contraceptive history, which may have affected recovery time. In contrast, all of the females who reversed after being given 9.4-mg implants had no prior contraceptive history. Finally, when either an unknown formulation or a 6-mg implant was used (n=10), one animal given the 6-mg implant conceived 2.27 yr later.

Statistical figures enter a gray area when attempting to calculate the average time that has passed since treatment for lions that have breeding recommendations, but have failed to conceive. Despite having relatively complete records for this species, there are many factors complicating our ability to predict when an animal may reverse. Life history traits, such as previous parity and age, affect fertility whether or not a female has received contraception. Cumulative effects of multiple contraceptive treatments may delay return to fertility. Moreover, preliminary data from lions show that recovery is complex and that some points in the pituitary-gonad axis are restored before others. So, while birth of live offspring is the gold standard for reversal, feedback concerning return of estrous behaviors and hormone monitoring is invaluable as well.

In addition to continuing routine collection of information about safety and reliability of contraceptives, the WCC is increasing efforts to collect reversal data, but to do so more efficiently. Our goal is to be able to provide more accurate estimates to veterinary staff and managers about durations of contraceptives, especially Suprelorin®. To accomplish this goal, we have identified plans of action targeted at different communities within AZA. One recent development that will positively impact AAZV members emerged from the partnership formed between the WCC and the European Group for Zoo Animal Contraception (EGZAC). Our annual contraception survey will transition from paper and electronic reports to online data entry; the interface will provide an easy-to-navigate, one-stop site for institutions to view the entire contraceptive histories of their animals. Online survey entry will be available 24/7 so that contraceptive information can be added when administered rather than through the tedious process of checking records to complete the survey once per year. Thus, this technology will make data submission easier as well as help fulfill the WCC’s need to flag records that are missing reversal information. This project is currently in the test phase and is expected to be rolled out to institutions in 2014.

While the WCC has identified and started implementing strategies to improve reversal feedback, suggestions and input from the AAZV are encouraged and welcomed. There should always be an open line of communication between the Center and zoo veterinarians so that we can address any concerns that arise, as well as provide the most current recommendations. As institutional feedback increases, we hope to collect enough data for proper analysis to serve as the basis of improved reversibility statistics to the zoo community, strengthening the foundation of the mission of the Center.


Speaker Information
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Mary Agnew, PhD
AZA Wildlife Contraception Center
Saint Louis Zoo
Saint Louis, MO, USA

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