For thousands of years, humans have selectively bred a variety of domesticated animals, creating many different breeds and unique types. While these historic farmers and breeders were focused on producing the highest quality of wool from sheep or the muscular build of a Rottweiler, they were unaware of other, more destructive traits that were passed on as well.
Genetics is the science of heredity and how specific physical traits are passed from generation to generation in any organism. Most everyone can relate to genetics from high school science courses showing color blindness in human males or if you have the ability to roll your tongue. But, serious, life threatening diseases are also often governed by our genes and this holds true for pets and other animals as well.
Take Penny, for instance. She was a Pembroke Welsh Corgi, a breed of dog known for excellent cattle herding skills and a love of family. Sadly, these Corgis are also known for a genetic condition known as Degenerative Myelopathy, or DM. This disease essentially causes damage along the spinal cord, leading to progressively worsening weakness in the rear legs. Eventually, Penny was unable to move her rear legs due to paralysis. She was humanely euthanized after a long life with a family she adored.
DM is not a treatable disease, but scientists have now pinpointed the mutation responsible for this illness. Almost four dozen different dog breeds have this altered gene present. Recent research has shown that only dogs who receive a copy of the mutated gene from both parents will develop the condition. This is known as a “recessive trait”. Other recessive conditions in animals include certain enzyme deficiencies in cats or some skin issues in horses.
Not all genetic diseases are this simple. Some are passed as dominant traits, some are linked to specific physical attributes and still others have multiple genes affecting the eventual outcome. Even the environment can influence the process of the disease or condition. Hip dysplasia in dogs is an example of a multi-gene and environmentally impacted problem.
The entire sequence of the canine genome was published in 2005. The genome of our feline friends was published around 2007 and just recently, the entire gene sequences of a Quarter Horse and a Thoroughbred have also been discovered. The good news in all of this is that as scientists and veterinarians better understand the root causes of hereditary issues, tests to find the disease and even possible treatment options become available.
Dr. Gus Cothran, professor at Texas A & M University’s College of Veterinary Medicine says that genetic testing will continue to prove to be of great value to veterinarians and even pet owners. “Imagine doing blood tests to find animals that are carrying certain mutations that might lead to deleterious conditions or diseases. Now, we can remove these animals from breeding programs before they are bred and help reduce the incidence of some very serious problems in our domesticated animals.”
Tests for degenerative myelopathy in dogs and polycystic kidney disease in cats are just two of the dozens of genetic screenings that are now available. Facilities like Texas A&M’s Animal Genetics Lab and the University of California at Davis’ Veterinary Genetics Lab provide testing for animals ranging from our dogs and cats all the way up to horses, llamas, pigs and cattle. Other private companies, for example, VetGen or DNA Diagnostics Center, have also started reaching out to veterinarians and pet owners interested in this sort of testing.
While these tests may not remove the possibility of genetic disease, they still can be very valuable. Knowing the chance for disease exists can prompt pet owners and veterinarians to start intervention programs, such as swimming or increased exercise in the case of Corgis, which might delay the onset or progression of the condition.
Anyone interested in breeding domestic animals should familiarize themselves with the potential for genetic diseases. Your veterinarian can be very helpful in determining what kind of conditions are considered hereditary and even help you find the resources to test the animals you want to breed.