Training Gorillas (Gorilla gorilla gorilla) for Noninvasive Semen Collection
American Association of Zoo Veterinarians Conference 1997
Corrine S. Brown, DVM
Omaha’s Henry Doorly Zoo, Omaha, NE, USA


Electroejaculation, a method commonly used for semen collection in exotic animals, generally results in poor quality samples from gorillas. Omaha’s Henry Doorly Zoo instituted a training program with a bachelor group of three gorillas (ages 10, 12, and 12 yr) to determine if semen quality would improve when collected in a noninvasive, nonstressful manner. This paper discusses the training process, and may be used as a guideline for other institutions initiating their own programs.

The Omaha Zoo’s training program was developed with several objectives in mind. The primary objective was to collect semen in a noninvasive, nonstressful manner. Secondary objectives included performing a cursory physical examination, providing behavioral enrichment, preserving normal gorilla behavior, and acquiring the capability to teach personnel from other institutions how to train gorillas for semen collection. The training techniques were developed and adapted to meet these objectives.

Appropriate behaviors, in response to verbal prompts, were rewarded with praise and food treats (Skittles, Division of Mars, Inc., Hackettstown, NJ 07840 USA). The behaviors were progressively refined to allow a cursory physical examination and semen collection. All three gorillas were taught the behaviors listed in Table 1.

Table 1. Trained gorilla behaviors

Verbal prompt

Behavioral response


Sit in front of the trainer


Touch a ping pong paddle through the mesh


Remain in position


Discontinue the current behavior


Move knee(s) to mesh and allow it to be touched


Move forearm to mesh and allow it to be touched


Place foot on mesh


Turn back to the trainer


Move chest to mesh


Move ear to mesh and allow it to be touched


Open mouth


Return an object dropped into the enclosure

All right, all done

End of training session

Collecting semen was the main goal of this training program. To accomplish this goal, two training techniques had to be established and consistently followed. First, gorillas were allowed to accept treats only with their lips, never their hands. Second, the trainer administered treats only with the right hand, never the left. This established a precedent which discouraged gorillas from moving their hands, and prevented the gorillas from expecting to find treats in the trainer’s left hand. Once these techniques were consistently followed, several behaviors had to be mastered before semen collection could begin. The gorillas were taught “station,” “target,” “knee,” and “hold” (Table 1). The completion of these behaviors resulted in the gorilla straddling a 7.5x15 cm steel sliding door that was built into the mesh caging. Once the gorilla reliably held this position, the door was opened by the trainer, and penile massage took place until the gorilla achieved an erection and ejaculated. While performing massage with the thumb and forefinger of the left hand, a small plastic bag (unopened) held in the same hand between the middle and ring fingers was used to capture the sample. The ejaculate volume, usually only a large drop, ranged from 10–140 µl.

Performing a physical examination, one of the secondary goals, was accomplished by stating the verbal prompt, and rewarding the animal when it performed the specified behavior. With the gorilla in the “hold” position, a PVC pipe was passed through the mesh. It was then used to touch the requested body part. The behavior was refined by stating the prompt and passing progressively shorter lengths of the pipe through the mesh. This encouraged the gorilla to move the body part to the pipe. “Knee,” “foot,” and “back” behaviors resulted in palpation of that body part through the wire mesh. “Arm” allowed small volume injections and may be adapted to allow venipuncture. “Chest” permitted auscultation. “Ear” allowed the otic temperature to be taken. “Mouth” made a visual dental examination possible.

Providing behavioral enrichment while maintaining normal gorilla behaviors was another objective of this program. Gorilla participation in the training sessions was voluntary. However, they were usually eager to shift into the training area on training days. They appeared to be mentally stimulated by the training. For example, one gorilla learned to “bargain” for treats by withholding an object dropped into the cage until the trainer demonstrated a large number of treats as a reward for the object’s return.

Because semen had never been collected from gorillas in this manner, the gorillas’ behavior when not in a training session was a concern. Therefore, the training routine was varied within each session, and some sessions omitted certain behaviors, including semen collection. Semen collection was incorporated as one of many behaviors a trainer may request of the gorilla. While the effectiveness of these techniques is debatable, there was no increase in the incidence of undesirable behaviors, such as masturbation, when the gorillas were not being trained.

The final objective for this program was to have the ability to teach personnel from other institutions how to train gorillas for semen collection. Therefore, visitors were welcome to observe training sessions. The gorillas expected strangers present during training, and they generally ignored them. This program has resulted in the additional benefit of easily accommodating photographers and journalists during the training sessions.

The Omaha Zoo’s gorilla training program has been successful. Over 175 semen samples were collected from the three gorillas since the initiation of the program. Collection of the first semen sample varied from 5–14 mo after the initiation of training, with collections occurring earliest on the animal that appeared to have the best relationship with the trainer. One animal produced consistently dead spermatozoa, but the other two animals produced samples that were good quality.1 These samples were regularly cryopreserved, which can rarely be accomplished with electroejaculated samples. One of the cryopreserved samples was used for in vitro fertilization, and resulted in a viable offspring.2

There are many benefits of developing a training program for semen collection in gorillas. Noninvasive semen collection involves no risk from anesthesia and results in good quality semen samples (N.M. Loskutoff, personal communication). Cursory physical examinations can be performed on a regular basis. Training also provides gorillas with behavioral enrichment.

As more institutions develop training programs for semen collection in gorillas and other great apes, artificial reproductive techniques have the potential to be routinely performed. The use of these techniques could lead to a more genetically stable population of captive western lowland gorillas, and may ensure the survival of the species.

Literature Cited

1.  Kurz, S. G., A.M. Barnes, J.W. Ramey, C. Brown, N.M. Loskutoff, L.G. Simmons, D.L. Armstrong, and C.J. De Jonge. 1996. Semen characteristics of a western lowland gorilla determined by manual and computer-assisted motion analysis. Proceedings of the 29th annual meeting of the Society for the Study of Reproduction, Fort Collins, Colorado.

2.  Pope, C.E., B.L. Dresser, N. Chin, J. Liu, N. Loskutoff, E. Behnke, C. Brown, M.A. McRae, C. Sinoway, M. Campbell, K. Cameron, O. Owens, C. Johnson, R. Evans, and M. Cedars. 1996. Birth of a western lowland gorilla (Gorilla gorilla gorilla) following in vitro fertilization and embryo transfer. Am. J. Primatol. (Accepted).


Speaker Information
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Corrine S. Brown, DVM
Omaha’s Henry Doorly Zoo
Omaha, NE, USA

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