D.L.
Hi J.,
My youngest grandson (almost 3 yrs old) has Autism and I have been in the special education field for 17 yrs now. Children (and adults) with Autism learn best with picture stories. Go on-line or to your local library or book store and research Autism and pictorial stories concerning appropriate touch with animals. You need to give a positive reward for being gentle and a negative consequence for being too rough.
You are actually fortunate that your child likes animals. Our little guy doesn't care for animals and our dog just loves him to death but every time our dog gets in "his space" he'll scream at the dog. It's sort of funny. He tolerates the dog to a point though. We took our grandson to a petty zoo thinking this would help but all he wanted to do was play in the gravel. So we let him play in the gravel because that's what he was happy doing.
Sometimes you have to just "pick your battles" and as long as your pet is tolerating the child's roughness, then ok ... the pet will let your child know when enough is enough. If you'd ever like to correspond in private, please feel free.
Blessings,
D.