Abstract

Male marine mammals in zoos and aquariums are sometimes maintained alone or in same sex groups. This type of housing is desirable for behavioral demonstrations, to prevent breeding, to control aggressive behavior, or to retain the genetic representation of animals for future reproduction. These management schemes may be complicated by undesirable male associated behaviors (aggression, excessive vocalization, anorexia, and loss of operant training). Castration effectively minimizes or controls unwanted male associated behaviors but anesthesia and surgery are required and it eliminates the animal's reproductive potential.

In this study, intramuscular administration of leuprolide acetate in a 1 month depot suspension successfully controlled undesirable male associated behaviors in California sea lions (Zalophus californianus) and California sea otters (Enhydra lutris) at the Aquarium for Wildlife Conservation. Leuprolide acetate is a long acting, but reversible, gonadotropin-releasing hormone (GnRH) agonist. Administration initially results in an increase in follicle stimulating hormone (FSH) and luteinizing hormone (LH) causing elevated testosterone. A progressive suppression then occurs reducing circulating testosterone levels to those of a castrate. Leuprolide acetate has been previously demonstrated to suppress testicular function in Atlantic bottlenose dolphins (Tursiops truncatus).

Three sea lions utilized for behavioral demonstrations developed aggression, anorexia, excessive vocalizations, and loss of operant conditioning and trained behaviors associated with seasonal spring and summer rut. Animals ranged from 10 to 23 years old and from 182 to 251 kilograms in weight. Each received 22.5 mg (0.09-0.12 mg/kg) depot leuprolide acetate at monthly intervals for 6 months (2 April-9 September 1996). Leuprolide was reconstituted with 1.5-9 ml diluent and administered in a pelvic limb by hand injection or projectile dart.

Four sea otters, which had been exhibited as an all male group, developed intra specific aggression and stress related behaviors (repetitive swimming and diving) as they matured. Eventually they could no longer be maintained as a compatible group. Otters ranged from 3.5 to 6 years old and from 20 to 33 kilograms in weight at the beginning of the study. Each otter received 3.75 mg (0.11-0.19 mg/kg) depot leuprolide acetate at monthly intervals. Initiation of drug administration in each otter was staggered so animals received 3-7 injections in a 6 month interval. Leuprolide was reconstituted with 0.5-1.5 ml diluent and administered in the dorsal surface of a pelvic limb by hand injection while the animal was confined in a restraint device. Marked testicular atrophy occurred in all otters with pre-treatment testicular length (55.67 ± 5 mm) significantly greater (Paired T test; p<0.05) than post-treatment length (38.33 ± 5 mm). Testosterone levels were determined at monthly intervals by radioimmunoassay. The youngest otter had testosterone levels below the assay detection limit (<O.05 ng/ml) on all sampling dates. Pre-treatment values for the other three ranged from 0.31-2.28 ng/ml. Testosterone levels decreased in these otters at one month post-treatment (<0.05-0.19 ng/ml) and by two months post-treatment all were undetectable.

One sea lion and 2 sea otters developed moderate to marked anorexia and depression with injection site lameness, pain, and swelling. Clinical signs were noted 5­17 days after injection and lasted for up to 3 weeks. Premedication or treatment with diphenhydramine was ineffective. Pretreatment with flunixin meglumine was not effective, but administration for 3-7 days after clinical signs developed was helpful in resolving clinical signs in the sea lion but not the sea otters.

Administration of depot leuprolide acetate was extremely successful in controlling male associated undesirable behaviors in both the sea lions and sea otters. During the rut period, the sea lions did not develop anorexia or aggression, did not vocalize excessively, and were able to be utilized for behavioral demonstrations. It became possible to maintain the sea otters in a compatible all male group. Advantages of using a GnRH agonist include no requirement for anesthesia or surgery and reversibility. Disadvantages are the drug cost, lameness at injection sites and other adverse reactions noted in some animals, and the necessity for frequent animal handling. Currently, subcutaneous administration and use of a 4 month depot formulation are underway in an attempt to address these limitations. This treatment has potential application for the control of male associated undesirable behaviors in sea lions and sea otters in zoos and aquariums if the disadvantages can be overcome.

Acknowledgements

We are grateful to TAP Pharmaceuticals for generous donation of depot leuprolide acetate, to Karen Drayer and the PKD Trust for financial support, and the veterinary technicians, animal keepers and trainers for their expert technical assistance.

References

1.  Briggs, M.B., W. Van Bonn, R.M. Linnehan, D. Messinger, C. Messinger, and S.Ridgway.1995. Effects of leuprolide acetate in depot suspension on testosterone levels testicular size and semen production in male Atlantic bottlenose dolphins (Tursiops truncatus). Proceedings of the IAAAM, Pp.112-114.