A rabbit with horn-like features has been found by a veterinarian in Minnesota.
http://www.washingtonpost.com/wp-dyn/content/article/2005/08/29/AR2005082901234.html
Is this the basis for the Jackalope story?
Probably not. “Real” Jackalope 
Maybe so. From the article.
“It had Shope papilloma virus, a highly contagious disease that causes rabbits to grow things on their head and face that look like horns.”
What does “RL” stand for?
Real Life, as in “not pretend”.
We found a rabbit like mentioned in the OP here at work a few years back, looked terribly bizzare. The “horns” looked like hair that had been glued into shape and were all over the rabbit’s head. Somebody got pics, not sure what became of them, or the rabbit.
Dang, no picture?
Not of this rabbit, but the effects of the disease can be seen here.
Hiding in plain sight, I am…
IIRC, there was no traditional Jackalope story; earlier this year, or maybe last year, the guy who “invented” the jackalope died. It made the offbeat news collections for a week or so; I probably wouldn’t have noticed if not for my (hastily-chosen) screen name.
Yeah, but what about a basselope ? (click the previous page button for a picture of a basselope)
Poor bunnies.
Well, that sucked the fun right out of this topic…
Oh, those poor little things! That’s just awful!