Ok, so I took my Yorkie to the vet to check his sperm count, and it turned out it was very low

. there were two females in heat at the Vets office, and he basically ignored them both
A neighbor of mine wants to use my Yorkie for her female, but as of now I am vry confused/ disapointed. My Vet suggested a series of hormone injections to try to jumpstart his testicles.
What do you think? any recomendation?
What would be the name of this hormone?