Honestly, I do not know much about this, so I don't want to just spitball here.

What I gather is that much of this still remains unknown.

What I would attempt to gather information on is, 1) is this congenital or is it controllable by diet/drugs", and then 2) to determine if anything can be done by diet?

If your dog has a 620 million count, with great motility, and if only 60% are normal, that means your dog has a 372 million effective count, which should still be enough to conceive.

The questions thus become, 1) if congenital, do you want to pass this trait along?, and 2) can those tweaked cells produce tweaked offspring? (My guess on the latter is no.)

I would certainly try to find out, via a reproductive vet, the answers to those questions.

Another question to ask yourself is, "Is this dog really worth all that effort?"

Is he really that good, so that no other options seem better?

Jack