07/16/2025
What is “COI” and how is it a useful tool in breeding purebred dogs?
COI or “coefficient of inbreeding” is a term used to describe the deleterious effects that inbreeding too heavily can have on not just one dog, but an entire family of dog’s overall health, including epigenetic health.
When I first started in Boxers in the early 2000s, it was very common for the “old timer” breeders to linebreed and even inbreed heavily, and then pull in bi***es from backyard bred pet stock as brood bi***es to help maintain the genetic health of their lines.
With the advent of health testing, social media and the push of the animal rights movement, these practices feel out of fashion. It was too difficult for a breeder to ensure cleanliness of health testing for dogs of an unknown pedigree—while the brood bitch tested may have been clear for a given disease, all dogs behind her were untested and unknown. And so, this practice fell out of favor and our genetic diversity grew smaller and smaller.
Around 2010, we began to see the effects of this. High incidence of immune dysfunction (the term “boxer colitis” had even been coined by vets due to immune dysregulation of the digestive system), cancers boomed, breeders couldn’t—for the life of them—get their bi***es to conceive whether breeding them naturally or via AI with tons of science and progesterone testing, and litter sizes of 5 or fewer puppies were considered normal. Newborn mortality was also high—puppies were born weak and failure to thrive was common. Other defects like cleft palettes and midline defects more common.
Breeders began to wake up. And while we refused to let go of the useful tools of health testing, we found alternative ways to diversify by using technology to analyze our pedigrees and planned breedings for lower rates of COI. Breeders began importing dogs from overseas. They began breeding based on penotype vs. genotype. And outcrossing became more common.
In 2015, I purchased a half German bitch from a dear friend of mine. Her name is Luna and she can be seen in my albums. Luna is the foundation for all of the dogs in my program.
I’m pleased to say that I’ve enjoyed the rewards of the low COI her pedigree has had to offer to my program and family of dogs.
My observations:
- Low/no allergies
- Predictable seasons
- Very high fertility rates
- No missed breedings
- First litter 10 puppies
- Second litter 9 puppies
- All puppies robust, fat and healthy, and came kicking and screaming into this world
- Fabulous early cognitive development—walking, ears, eyes open early
- No midline or other defects
- No mono/cryptorchidism
- No “boxer colitis”
These things seem to be holding true with her daughters as well.
For more information about COI, visit The Canine Institute of Biology: https://www.instituteofcaninebiology.org/blog/coi-faqs-understanding-the-coefficient-of-inbreeding
