OUCH!! Poor little Louis!! My Angel got one of her toenails ripped off by a weedeater on the other side of the fence. I never thought about that string coming under the fence and it got her. She didn't make a sound but then she just wouldn't move and the blood started coming out of her paw. I rushed her to the vet and they didnt know if her nail would grow back or if it had actually taken off the top knuckle along with it. They bandaged it and had to keep that on for a few days. She milked that for all it was worth!
Anyway, good news is that it did grow back and she still has no clue with the relationship with the weedeater and her toe since it was so quick.
Hope your little one gets better soon. Keep it clean and dry with anticeptic ointment.