Hi y’all! My name is Sasha Adams and I am a fourth year veterinary student at Texas A&M College of
Veterinary Medicine. I had the incredible opportunity to complete an 8-week preceptorship at Fossil Rim Wildlife Center to learn more about veterinary medicine in semi-free range facilities and to get more hoofstock immobilization experience in the process.
During my preceptorship, I had the opportunity to learn about the various breeding programs at Fossil Rim. This includes when to breed different species of animals and sometimes, more importantly, when not to breed.
During the late fall, around late September to October, the team at Fossil Rim sets out to do “bull
swaps” in the sable, gemsbok, waterbuck, and addax herds. This means that the dominant breeding
herd bull is swapped out with an epididymectomized bull in order to time parturition (or birthing) just right for the females. Since gestation is about 9 months in these species, the goal is for the females to give birth in the spring, and not in the heat of the summer or late winter.
What is an epididymectomy?
An epididymectomy is a surgical procedure where a part of the epididymis is removed. The epididymis is a tube on the side of the testicle that matures, transports, and stores sperm. A portion of the vas deferens, the tube that transports sperm to the outside portion of the reproductive tract, is also removed. This procedure effectively interrupts the pathway of sperm so that the animal cannot impregnate a female.
How is epididymectomy different from castration?
As opposed to castration, these animals’ testicles are not removed with an epididymectomy, but rather the tubes that transport the sperm from the testicle to the penis are cut. This prevents the male from successfully impregnating females as it creates a “road block” in the passage of sperm to the penis and therefore, to the female. Testosterone is still produced by the testicle, so the male is able retain secondary male sex characteristics, such as antlers in fallow deer.
Why are secondary male sex characteristics important to retain?
These animals can still detect heat/estrus in females and can participate in “rut”, which is another name for breeding season. Participating in rut is part of these males’ natural behaviors, as in fallow deer. In a semi-free range facility such as Fossil Rim, the key is to retain as much of these animals’ natural behaviors as possible
Once the fallow deer at Fossil Rim are epididymectomized, their testosterone levels will function the
same as they did before. They will still have peak levels of testosterone during rut and low testosterone levels after rut. They will still shed their antlers the same as before. This is in contrast to castrated males that will typically never re-grow their antlers after castration due to the lack of testosterone. Therefore, epididymectomies are an excellent option for display animals; such is the case at Fossil Rim.
In other herds of exotic bovids, such as sable and gemsbok, the epididymectomized bull maintains the social structure of the herd (i.e. dominant male with multiple females). Since the sable, gemsbok, waterbuck, and addax females are used to having a dominant bull out with them, an epididymectomized bull is a great alternative to maintain social hierarchy, while still controlling the reproduction of the herd.
What are the other benefits to epididymectomies?
Since Fossil Rim is a semi-free range wildlife park, it is important that these animals are able to maintain most of their natural behaviors. Epididymectomies allow this, while still making sure that there are adequate resources for all animals and preventing over-population, as well as making sure the animals are birthing calves at the best time possible. In addition to these benefits, epididymectomies are much less invasive than a castration and arguably faster. This is important because the goal is to be the least invasive as possible. This leaves less room for complications with surgery or infection.
I hope you enjoyed learning about epididymectomies and why we do them at Fossil Rim!