Hollywood can really screw things like that up. Lassie was played by a male and I think Potter's wife was named Sophie, could be wro uh mistaken there. LOL and yes the horse was a gelding and the replacement horse had a different blaze if memory serves me.
I first saw M.A.S.H. 4077 after I got out of the Navy and I hated it and wouldn't watch it.
I thought they were mocking our service men, and the original movie probably was.
After some years I found myself watching it on re-runs and learned to like it.
Gabby