The constant hunger thing is a feature of insulin-resistant and leptin-resistant horses, but it does decrease as the diet gets tightened and balanced; exercise will also help reduce insulin levels.  What I can't tell you is how long this will take, as each horse is different, and some stay as ever-hungry gannets forever.  My crew took about 3 or 4 years of controlled feeding to lose that excessive hunger, but it did happen. 
--

Jaini Clougher (BSc,BVSc)

Merlin (over the bridge) ,Maggie,Gypsy, Ranger

https://ecir.groups.io/g/CaseHistory/files/Jaini%20and%20Merlin-Maggie-Gypsy