Retained Testicles Litter

Hello everyone. I am a dog breeder of spaniels and have had two litters using the same sir and Dam. The first litter was a straightforward pregnancy and birth for mum delivering 10 healthy puppies including 7 males who all have both testicles. litter number 2 was a difficult birth where mum would not feed the puppies for the first 2 days and they had to be handfed. She was diagnosed with an infection by the vets which she had to be treated for. The issue with this litter is out of 7 male puppies born only 1 male puppy has both testicles descended at current age of 5 months. The others only have 1 testicle descended. I guess my question is here does anyone have a similar experience? I have read that this can be genetic but it has not presented itself at all in the first litter. If it had we would not of bred the dogs again. Or I am wondering if external factors could have been at play such as mum not being able to interact with the puppies in the first few days which I have read is a key time for the testicles to descend. any advice and opinions greatly welcomed!

Hello - Here is a post by the well-known media vet Joe Inglis, outlining a basic description of retained testes:  https://vethelpdirect.com/vetblog/2010/03/24/harveys-retained-testicle/ There is a ligament called the gubernaculum, a long cord that attaches the testicle (which starts life next to the kidney, in the tiny pup) to the bottom of the scrotum.  The two points are obviously a long distance away from one another within the newborn, but my understanding is that the pup grows faster than the ligament which consequently becomes taut and, in normal males, pulls the testicle towards the adult position in the scrotal sac.  In cryptorchid dogs, this process gets interrupted and the testicle doesn't fully descend.  Undescended testicles are thought to have a genetic basis and, in particular, are strongly associated with one particular gene called HMGA2.  But alas, it's rarely that simple! - multiple genes code for the descent of testicles and females dogs can carry the genes as well as the male.  Developmental factors may also influence the process.  So the genetics turn out to be an imperfect predictor, as you have found out.  It is sometimes recommended that any pups are sterilized before leaving their parent in order to avoid passing any genetic basis for the condition on to the next generation.