If we can how can we do it ??
It is possible if the horses have similar proportions. I did the exact same thing with that rig to another horse. You need to use the mesh from the rigged horse.
Clean up the rigged (white) horse – make sure the mesh is just a shell – i.e. the body is currently a closed cylinder, remove the end caps so its just a shell. Do this for as many body sections as possible.
Scale the new horse to the same size as the white horse (as close as possible). Make sure you apply the scale.
Select the white mesh, shift-select the new horse mesh, then press spacebar and type “transfer weights”
select “nearest surface point” if asked.
This takes the weights from the white mesh and transfers them to the new mesh. Now, parent the new mesh to the armature (with modifier, but NOT with any of the options --NOT automatic painting, NOT empty groups, etc)
I can’t understand what you mean by cleaning the mesh. Whenever i select the white mesh and enter edit mode the mesh vanishes.
Then it is hidden, press ALT-H
Well I did alt h but I cant understand what you mean by cleaning it. Its a proper mesh not a cylinder with cap ends. Its the whole horse there is the head and then there is the body.
Then ignore that part. Hopefully it will still work.