Abstract

There are few available methods of chemical contraception in marine mammals, and none frequently used in cetaceans. To properly manage any species, the ability to regulate the reproduction of the animals is essential. In many cases there is a desire to increase reproductive capacities of certain individuals or groups while in other cases there is a desire to decrease or stop reproduction in an individual or group. To facilitate the proper management of Atlantic bottlenose dolphins (Tursiops truncatus), a GnRH agonist, leuprolide acetate in depot suspension (Lupron®), was used to evaluate effect on testosterone levels, testicular size, and semen production.

This study was conducted at three sites. The Chicago Zoological Society (CZS) maintains two breeding populations of dolphins. One at its Brookfield Zoo facility in Brookfield, Illinois, USA and the second is at its off-site breeding and research facility, the Dolphin Connection at Hawk's Cay Resort and Marina7 Duck Key, Florida7 USA. The United States Navy maintains dolphins at Naval Command Control and Ocean Surveillance Centers RDTE Division (NRaD) in San Diego, California. USA.

The study group of animals consisted of ten animals eight treatment and two controls. Of the ten animals six were in the CZS group and four were at the Navy facility. All animals received the ultrasonic evaluations (Table 1). All CZS animals were in the treatment group while two of the Navy animals were treated and two were controls. Semen was consistently collected on three of the animals at the Dolphin Connection facility (CZS group).

The treatment dolphins were injected with 0.075 mg/kg Lupron® every 28 days for six months. The control animals were injected with an equal volume of the copolymer suspension without the active ingredient, leuprolide acetate. During this period, blood samples were taken as noted in Table 1. Blood was collected by venipuncture of the fluke vessel and the whole blood was placed in a thrombin tube. After the clot had formed the tube was spun in a centrifuge and the serum was decanted into plastic vessels for storage in a -70° C freezer until analysis. Ultrasound and semen collection were performed at monthly.

Testosterone values were determined by using the radioimmunoassay I¹²⁵ testosterone test kit.

During the study period, the testosterone levels dropped from 15-40 ng/ml to consistent levels of < 0.45 ng/ml, testicular size was reduced during the period, and semen production dropped from levels as high as 3.0 X 10⁹ sperm /ml to 0-10,000 sperm/ ml, for the test animals. The sonographic image of the testes changed from that of a distinct, well circumscribed tissue to a very diffuse pattern that made both visualization and measurements difficult. Upon cessation of treatments, the size of the testes, the testosterone levels, and the sperm production resumed to pre-trial levels. There were no changes noted in the two control animals.

It appears Lupron® effectively decreases testosterone levels, testicular size, and sperm production. The use of this product may lead to an effective reversible means of male contraception.

Table 1. Protocol for Lupron® Study

1.  Blood collection was performed by phlebotomy of the fluke vein. Serum was obtained from the sample after centrifugation.

2.  Ultrasound: all animals in the study received the ultrasonic examination. The Navy dolphins were examined by removing the animals from the water and examining them on the dock. The CZS animals were examined in the water where they stationed in a lateral layout.

3.  Animals received deep intramuscular injections via a 3 inch, 18 8a. spinal needle.

4.  Three of the males at the Dolphin Connection facility were trained for semen collection.

Acknowledgements

We would like to thank Vicki Hedgepeth at the Department of Animal Science, North Carolina State University for evaluating the serum samples for testosterone levels and thank the trainers at all facilities who took the extra time to work the animals and maintain behaviors during the study. Without the collaboration of all the contributors, the study would not have been possible.