by Zoo Veterinarian Dr. Louise Beyea
The arrival of spring is often accompanied by the arrival of babies for many animals in the wild.
Having babies is usually a good thing. It means the species lives on.
Mother Nature can usually ensure that there’s plenty of space for new babies, and “herd
dynamics” often ward against related family members mating and creating inbred offspring.
Wild animals living in captive situations are a different story. There are no carnivores to dine on
the new bunnies that are born each spring. There are no new territories for the excess bachelor
males to inhabit. So even though babies are cute, perpetuate the species, and make for really
great viewing at the zoo, there are times when we DON’T want animals to have babies in the
captive wildlife world.
In some instances, our way of managing reproduction is the same way we manage reproduction
in our pets: spaying and neutering. Surgical sterilization works well when we have species that
are readily available, such as with our barnyard petting zoo animals or the domestic animals that are ambassadors for educational programming.
When managing reproduction in species that are more exotic than goats and rabbits, spaying
and neutering is usually not performed because we desire to maintain the future breeding
capability of the animals. For example, we might not want to have more lemurs born in 2020
because we don’t have the space for more lemurs right now, but more lemurs might be
desirable in 2024 as some animals are transferred to other zoos for breeding purposes and
older animals die off. Spaying and neutering eliminates future options for more babies.
Deciding who gets to have babies and when they get to have babies is a complex process that
involves a lot of statistics. Breeding decisions at the Lake Superior Zoo are made in accordanc
with Species Survival Plan (SSP) objectives of the Association of Zoos and Aquariums. In the
most simple terms, the SSP manages a scientifically-designed mating game to control the
number of animals in captivity and the family trees of those animals.
Statisticians evaluate each captive population to determine how many animals need to be born
each year to maintain an adequate number of unrelated animals in accredited zoos. Sometimes
that means there needs to be a lot of monkeys giving birth if monkeys are in short supply. But, if
there are not enough zoos with enough space to house a certain type of monkey, the birth of
more offspring needs to be curtailed.
Breeding partners are matched based on their family tree. The idea is to eliminate parent-to-offspring,
sibling-to-sibling, or cousin-to-cousin matings to avoid inbreeding, which can lead to
birth defects in the resulting offspring.
Each year, the Lake Superior Zoo receives recommendations from the SSP on whether to allow
breeding of each particular species, or not. Every year, we update our preventive health care
plan for each species to include the latest recommendations for breeding or contraception.
Monkeys and lemurs at the Lake Superior Zoo are the most common species to require
contraception. “Apes and monkeys are perhaps the easiest species to treat with
contraceptives,” according to the AZA’s Reproductive Management Center. “Many products
developed for humans are safe and effective in non-human primates.” In humans, the synthetic
hormone etonogestrel is used as a long-acting contraceptive. In non-human primates, we use
the drug melengestrol acetate (MGA) for birth control. As in humans, the drug is in an implant
that is inserted under the skin and the drug is gradually released into the body over a period of
In 2020, we have three primates that are allowed to reproduce and eight that are prevented
from breeding. Of those eight, four require to have their contraception implant replaced in 2020.
Every two years, we remove the old implant and replace it with a new one in animals that are
not going to be allowed to reproduce.
Replacing the implant is an easy process, but try telling that to a monkey! The procedure is
quick and simple and could be done under local anesthesia as it is in humans, but we perform
the surgery under general anesthesia because monkeys are not great at following directions
and sitting still.
Our first task is to get the animal under anesthesia, which usually involves a combination of
injected drugs and inhaled gas anesthesia. After we remove the hair from the surgical site, we
then clean the site with a disinfectant soap and alcohol. Then, the skin is incised, the old implant
is grasped with forceps and removed, and a new implant is inserted in its place. The skin
incision is then closed with dissolvable sutures that are placed below the level of the skin
surface. The implant is placed in an area where the monkey can’t reach the site and scratch at
the incision. Unfortunately, we can’t prevent another animal in the group from picking at the
surgical incision when buddies are grooming each other. Keepers check daily to be sure there
are no problems at the implant site.
The complications we’ve observed over the years include loss of the implant (most likely
because of too much grooming from another monkey friend), and pregnancy despite the
presence of the implant.
When the SSP determines that more of a specific species of monkey is needed for AZA zoos,
we remove the implants and allow the animals to reproduce. In primates, return to normal
fertility is usually successful if the female is still in her prime reproductive years.
If you want more detailed information about birth control in zoo animals, check out the web site
of the AZA’s Reproductive Management Center which is housed at the St. Louis Zoo here.
If you have enjoyed this blog, wish to have questions answered, or have ideas for other zoo
topics you’d like to see addressed, please send me an email. You can find me at
firstname.lastname@example.org. Here’s to keeping it wild until next month!