With puppies on the horizon at the end of the month, our thoughts turn to what we might get (well, puppies, hopefully, LOL), what colour they might be (the genetics of these matings tell us it could be anything!), will they be boys or girls (which is determined by the sire), and will any of the boys be cryptorchid. Ultrasound and x-rays tell us the number to expect, so not everything is idle speculation, fortunately.
But of all the things we can't yet predict, cryptorchidism, (also known as retained testicles) where a puppy's testicles fail to fully descend into the scrotal sac (scrotum) after birth, is the most heartbreaking.
Latest research suggests cryptorchidism might be influenced by at least three genes but in many pedigrees it's a simple autosomal recessive that is sex limited. That means both males and females can be carriers, so dad and mum both contribute to the problem, but, of course, only males show the defect (the same happens with haemophilia in humans, although in that case, only the female carries the gene, not both parents, and only the boys manifest the condition).
Dr Max Rothschild PhD, Distinguished Professor of Iowa State University is working on the genetic aspects of cryptorchidism through a grant from the AKC´s Canine Health Foundation. According to him, “This seems to be a complex trait controlled by multiple genes and is caused not only by genetic components but also by epigenetic and environmental factors.”
If a cryptorchid puppy shows up in a litter, you can safely assume the father is a carrier and mum is at least a carrier if not homozygous for the trait. Sadly, no fertility problems have been identified in carrier or homozygous girls or obvious defects to help identify them before breeding.
So, how do we know the dog is a cryptorchid and not just a "late developer"? According to Dr Shauna O'Meara BVSc (Hons) from Pet Informed Online, "Most texts define cryptorchidism as the condition whereby one or both testicles are not present within the scrotal sac of the animal (dog or cat) by 8 weeks of age. Using this definition, animals whose testicles have not descended into the scrotum by this time should ideally not be bred from and should be considered cryptorchid. Certainly, many of the textbooks state that if a male animal's teste/s have not descended by 2 months of age, then they are very unlikely to. Other texts are a little more generous, allowing the animal up to 16 weeks before deeming the animal's gonads unlikely to descend."
Our first 2 pet Chihuahuas (Loki and Fat Freddie) were cryptorchid and, coming from an ethical breeder, the reason they were pet homed in the first place. They were both neutered around 7 months of age, the retained testicles removed from the abdomen and they are still living large and well at the age of 11 and 10 with no harmful side effects.
So what's the big deal, you ask? Loki and Fat Freddie are fine.
Yes they are, because as neutered dogs, they are no longer prone to a number of significant and potentially life-threatening medical conditions. These include: testicular torsion, testicular cancer and various testicular-cancer-related conditions such as male feminizing syndrome, oestrogen toxicity (this causes severe pancytopenia: a complete deficiency in the numbers of red blood cells, white blood cells and platelets in the animal's blood) and the hyper-secretion of androgens such as testosterone.
But happy and now as healthy as they are, Loki and Freddie come from the same pedigree lines as so many NZ Chihuahuas (there are a few NZ sires who appear on almost every pedigree in NZ), and are closely related to several of our breeding girls. Loki would have killed it in the show ring, he is such a stunning boy, but neither dog was allowed to show (it's a disqualifying fault) or breed so they could pass on the fault. Since we began working with EBVs (Estimated Breeding Values) we have painstakingly tracked back what we can through our lines to identify possible carriers of these as yet unidentified genes in our distaff lines, and mate them to clear sires.
It's easy to tell when you have a cryptorchid boy (who can be neutered and pet homed), but not so much the girls. Having imported sires helps because they have no genetic connection to the NZ lines, which helps to narrow down the carriers. One day, we might be able to DNA test for this as we do for other genetic conditions like PRA, but sadly, we're not there yet.
Because we have ruthlessly cut all cryptorchid boys from our breeding lines (we still weep over Baron and a couple of other stunners we've bred along the way who had everything we could ask for in a show dog but two balls!), we are seeing a marked decline in its occurrence in our lines. But the time-bomb lingers. It will take many generations to eliminate it completely (the recommended number is 40 clear puppies from one sire or dam to be certain - which is actually not physically possible when you only do 2 litters per girl in a breed that averages 2-4 pups per litter!) but in the meantime, we wait, carefully track the lines and keep our fingers crossed.
There are some really interesting articles about the health and ethical implications of breeding from crypotorchid dogs (see the references at the end of the post) if you'd like to know more. For veterinarians, in particular, deliberately breeding from cryptorchid dogs is a very touchy subject. Dr Shauna O'Meara BVSc (Hons), who authored the article on the Australian Pet Informed website, is particularly scathing about the (hopefully rare) practice of surgically relocating the retained testicle in show dogs.
Dr O'Meara writes: "The artificial induction of testicular descent, whether this be through medical or surgical processes, must always be considered questionable from an ethical viewpoint. The condition is a hereditary defect with medical implications for the affected animal and any of its affected offspring. The deliberate breeding of any animal with such hereditary defects should be frowned upon as unethical because of the detriment to the breed's quality overall and because of the suffering and pain (cancer, testicular torsion etc.) that might be experienced by afflicted dogs further down the line.
The practise of inducing testicular descent artificially should also be considered unethical from a business viewpoint too. The whole reason why breeders and showers of dogs and cats seek to get their animal's testicles corrected is to deceive show judges, prospective breeder clients and prospective animal buyers into thinking that their animal is genitally and genetically sound. This results in more ribbons at the show, more stud-dog sire demand and more pups sold to the deceived buyer, but in doing so, it essentially robs the ethical showers of their deserved success and defrauds the owners of breeding bitches and queens who subsequently have their females mated to that prize-winning, but defective stud."
Thankfully, the majority of NZ Chihuahua breeders are far too ethical and honest to do anything so fraudulent or detrimental to their own dogs' health, but unless and until we can identity the genes responsible and their carriers, there is always the chance that no matter how careful, the time-bomb will go off when we least expect it, and probably in the prettiest, most show-stopping prospect in the litter. Sigh.
Suggested Reading for medical geeks:
Clinical and Diagnostic Evaluation of the Male Reproductive Tract. In Feldman EC and Nelson RW: Canine and Feline Endocrinology and Reproduction, 2nd ed. Sydney, 1996, WB Saunders Company.
Disorders of the Testes and Epididymides. In Feldman EC and Nelson RW: Canine and Feline Endocrinology and Reproduction, 2nd ed. Sydney, 1996, WB Saunders Company.
Reproductive and Hormonal Functions of the Male (and the Pineal Gland). In Guyton AC, Hall JE, editors: Textbook of Medical Physiology, 9th ed. Sydney, 1996, WB Saunders Company.
The Urogenital Apparatus. In Dyce KM, Sack WO, Wensing CJG editors: Textbook of Veterinary Anatomy, 2nd ed. Sydney, 1996, WB Saunders Company.
The Pelvis and Reproductive Organs of the Carnivores. In Dyce KM, Sack WO, Wensing CJG editors: Textbook of Veterinary Anatomy, 2nd ed. Sydney, 1996, WB Saunders Company.
Appendix 3. Congenital Defects of the Dog. In Ettinger SJ, Feldman EC, editors: Textbook of Veterinary Internal Medicine, Sydney, 2000, WB Saunders Company.
Memon MA, Mickelsen WD, Inherited and Congenital Disorders of the Male and Female Reproductive Systems. In Ettinger SJ, Feldman EC, editors: Textbook of Veterinary Internal Medicine, Sydney, 2000, WB Saunders Company.
Canine Reproduction. In Daris W, editor: Compendium of Animal Reproduction, 5th ed. 1998, Intervet.
Hayes HM et al, Canine Cryptorchidism and Subsequent Testicular Neoplasia: Case Control Study with Epidemiological Update. In Teratology 32:51, 1985.