Neko Kawaigari! ~Crane Inuneko Byouin Shinsatsuchuu~

In this world, humans with dog or cat ears are commonplace.

Jack, the protagonist, is a dog-man of a large, gentle breed. He works as the assistant for Dr. Crane, the head doctor of a secluded animal clinic where various cat-girls are being treated. Jack has no memory of his life before coming to the clinic, and he works for Dr. Crane to repay her kindness after she took him in. While working hard with the doctor and enjoying his life with the patients, Jack lives a calm life.

With the exception of having to treat said patients, that is...
The method of treatment is mainly sexual conduct with the patients. Jack has no choice but to obey Dr. Crane's orders and do these things...
Doing this over and over for days, Jack begins to have his doubts. But he has to remind himself it's all for the wellbeing of his patients.

And of course, even he can't resist his urges sometimes...
For this man with an unknown past, the clinic is his everything.

[description from Getchu]