Those areas are very sensitive. make sure you spray them well with grooming spray, before brushing so any tangles come out easily. Never brush them dry.
I would suggest using a grooming arm. I attach mine to the counter top. Then I lift up their front legs and brush the belly. they don't object because it doesn't hurt.
To do the rump, I just hold my hand under their bell so they stand. the grooming arm keeps them from trying to get away. They also have double nooses for the grooming arms, one for the neck and one for the belly. |