I'm not a breeder, just a dog nerd, so this isn't a professional perspective.
I do believe it's quite common for sperm viability to decline in age. Some breeders collect and store semen from especially nice males when they're young for this reason - I've known a couple litters that were even 'sired' by a male who had passed on some years before. Obviously this is expensive so most of the time when it's done it's because the male is truly exceptional in some way. You can get a sperm evaluation at a vet to confirm whether your male is experiencing reduced virality or this past litter was just a fluke.
Singleton puppies are more common in very small-toy breed dogs - not sure which size of Eskie you're breeding - but not exactly desirable. While they sometimes do fine, singleton pups do lack that important social learning most puppies get from their littermates. Play and interaction with littermates are building blocks to important lifelong behaviors like good bite inhibition, learning impulse control and frustration tolerance, and overall resilience in stressful situations. Some breeders who work with breeds known for very small litter sizes (1-3) try to always breed two females close together, so there's a higher chance of having more than one puppy between the two so the babies can get those important 'littermate' interactions, even if they're not technically related to each other. So that's all something to keep in mind.
For me the big reasons not to breed an older male would be:
Obviously this is excluding all the criteria a stud dog of any age should meet, like genetic health screening, passing a veterinary pre-breeding health exam, being free of structural deformities etc.
I do believe it's quite common for sperm viability to decline in age. Some breeders collect and store semen from especially nice males when they're young for this reason - I've known a couple litters that were even 'sired' by a male who had passed on some years before. Obviously this is expensive so most of the time when it's done it's because the male is truly exceptional in some way. You can get a sperm evaluation at a vet to confirm whether your male is experiencing reduced virality or this past litter was just a fluke.
Singleton puppies are more common in very small-toy breed dogs - not sure which size of Eskie you're breeding - but not exactly desirable. While they sometimes do fine, singleton pups do lack that important social learning most puppies get from their littermates. Play and interaction with littermates are building blocks to important lifelong behaviors like good bite inhibition, learning impulse control and frustration tolerance, and overall resilience in stressful situations. Some breeders who work with breeds known for very small litter sizes (1-3) try to always breed two females close together, so there's a higher chance of having more than one puppy between the two so the babies can get those important 'littermate' interactions, even if they're not technically related to each other. So that's all something to keep in mind.
For me the big reasons not to breed an older male would be:
- He's sired a lot of litters and is overrepresented in his breed's gene pool ('popular sire syndrome').
- He has developed signs of a serious health, structural, or behavioral problem in his old age that may be genetic and shouldn't be passed down to potential future puppies
- He has a physical issue that would make the act of mating dangerous to him (like certain back injuries)
- Risk of low fertility/small litters (as I addressed above)
Obviously this is excluding all the criteria a stud dog of any age should meet, like genetic health screening, passing a veterinary pre-breeding health exam, being free of structural deformities etc.
