Re-assessing the reversibility of melengestrol acetate (MGA) implants in golden-headed lion tamarins (Leontopithecus chrysomelas): a comparison with golden lion tamarins (L. rosalia)
The reversibility and flexibility of contraceptive methods generally allow for improved genetic and demographic management of captive populations. Earlier studies have produced conflicting results regarding the restoration of reproduction after using melengestrol acetate (MGA) implants in golden-headed (Leontopithecus chrysomelas, GHLT) and golden lion tamarins (L. rosalia, GLT): two closely related species that are physiologically and genetically very similar. The present study investigates the nature of this inter-species difference, presents new data on GHLTs and compares this with published data on GLTs. Analyses showed that around 34% of the GHLTs resumed breeding after their MGA implants were removed or had expired. Non-implanted GHLTs (control group) were significantly more likely to reproduce than females previously treated with an MGA implant, regardless of whether the implant was removed or left to expire. Younger and parous female GHLTs in the control group were more likely to start reproducing. In implanted females, only parity had an impact, with parous females being more likely to resume breeding than non-parous females. In contrast, data published on GLTs indicate that 75% of GLT females resume breeding, and that removing the implant increases the probability of reproduction occurring. Available data suggest that the observed inter-specific differences are related to differences in the weights of the implants used for the two species. For GHLTs, adjusting MGA doses and/or the sizes of the implants currently administered may be required in order to preserve the reproductive potential of individuals. Apart from potentially negative medical and welfare consequences for individual GHLTs, the reduced reversibility of MGA implants also impacts on management practices used to achieve the objectives of conservation breeding programmes. Finally, this study stresses the importance of evaluating the suitability of contraceptive methods at a species-specific level.
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