Cryptorchidism in a Litter: What Should a Breeder Do?
After a recent webinar, I received an excellent question that many breeders struggle with. Here’s a slightly shortened version:
“Two outstanding dogs, healthy, with excellent temperaments and conformation, and no known cryptorchidism in their families, produce a litter of 10 puppies. By six months, 3 of the 5 males are diagnosed as cryptorchid. I’ve read that a female producing 50 % or more cryptorchid males is homozygous recessive and should be removed from breeding. Is that right? What about the father? And what about the littermates: can they be bred with caution, for example with a partner from a more distant family line?”
How is cryptorchidism inherited?
It’s often described as an “autosomal recessive, polygenic” trait, but a trait can’t be both:
- An autosomal recessive trait is caused by one gene. A dog is affected when it inherits two copies of the same variant.
- A polygenic trait is influenced by many genes, each with a small effect. There’s no single variant and no clear “carrier”.
An older theory described cryptorchidism as a single-gene, sex-limited recessive trait. Current research shows that it’s polygenic, and that epigenetic and environmental factors, such as hormone-disrupting chemicals during pregnancy, also play an important role. Its heritability is low: around 11 % in a large Dutch study of Boxers, and close to zero in a population of Labrador and Golden Retriever assistance dogs. There’s no DNA test.
Both parents contribute. Only males show the trait, but females carry and pass on the genetic risk just as much.
The 50 % rule and the parents
The 50 % rule comes from the single-gene model, so it doesn’t apply. There’s no “homozygous” female in a polygenic trait, and the female isn’t more responsible than the male.
Still, three affected males out of five is a clear signal that this combination brings together many risk factors, genetic and possibly also shared environmental ones during the pregnancy. Interestingly, a Dutch study of more than 11,000 litters found that litters in which both parents had produced cryptorchid puppies were, on average, larger. In practice, I would:
- not repeat the combination,
- consider using both parents again with caution, each with a partner whose close family is free of cryptorchidism, and
- follow those litters closely. If the problem appears again, stop using that dog.
The father and the mother are treated the same way.
The littermates
Their risk is less certain than their parents’: some may have inherited more risk factors, some fewer. If they turn out to be excellent dogs, I wouldn’t exclude them automatically. Choose a partner from a more distant family line with no known recent cryptorchidism, start with one litter, and evaluate the result before using the dog more widely. The more cryptorchid relatives a dog has in its close family, the more careful you should be.
Why not be stricter?
A cryptorchid dog can usually live an easy everyday life. The condition should be taken seriously, but not handled in a way that costs more than it gains. In a small breed with a narrow genetic base, excluding every relative of every affected dog would remove a large share of the breeding stock and weaken the breed in other ways.
What helps most is information. If breeders report every cryptorchid male to their breed club, the club can follow which families and combinations produce it. With enough data, it can even calculate risk scores based on affected relatives.
Watch the webinar recording
This question came after my webinar The Health and Welfare of the Swedish Vallhund, which covered breeding for health, genetic diversity and practical breeding decisions in a small breed. You can still get the recording: register here by 31 October 2026, and you can watch it until 16 November 2026.
Single-gene and polygenic inheritance, and how to breed against each, are covered in my online courses here >>.