It would be preferred if it was the pet, like a dog/cat, but some kind of animal is good. I'm guessing it would be fantasy XD
It would also be preferred if the uke wasn't all girly and he was rather tough.

Sentimental Garden Lover

Inu mo Arukeba Fallin' Love
Koibito wa Hatsujouki ch5 (ch6 + Ch7 are mini chapters that involve guys fantasizing about the scenario you described)
Suzu no Ne ga Kikoeru

none of the ukes in the above stories are "tough."

Tsuki ni Hoero this one is about a werewolf but sometimes he's pure wolf form and other times human form so I though it might still fit what you're looking for

Something like Love Neko?

It's the Art of Time, it's the Art of Life--
Of the player and the craftsman,
Of the writer of songs, of the creator of love,
Of those who will follow, of those who led,
There's no other way in the world ahead ♥

Lucky Wolf
Tsuki ni Ookami ch3, the first story the uke is a animal