Pony getting big round belly

[Jxmxg]

I have a gypsy cob pony gelding who will be 3yrs old in May. His belly is looking pretty big and round latley. He is in a big field with two bigger horses and we only moved a temporary fence over each day so they get to share a new section of grass per day but maybe this is what is causing him to be getting a big belly? It doesn't seem like much grass tho. The half of the field they are on doesn't have any grazing left on it but the other half is full of grass but the fence is only moved over a little per day. He isn't getting any hay right now. He gets a powered vit and min supplment (equimins tip top) dampened down with a handful of mollases free dengie chaff and a teaspoon of crushed himalayan salt per day) also has a block of himalayan salt in the field). He has been dewormed just over a week ago and is long reined down trails at walk and some trot or put loose in arena to run and play for about 15-20mins per day. Do you think I should move him to a small paddock by himself with no grass and give him some hay? Don't think he will be happy about that but not sure if it's the grass making him look bloated?

*Pictures below are from two weeks ago. Will get new ones today* his belly is bigger now than in these pics.

 

[windand rain]

No giving hay instead of a small amount of grass will provide too many calories and reduce his movement. He needs more movement not less. His tummy is a store for winter and as long as you dont stuff him full of food over winter he will lose it naturally

 

[The Xmas Furry]

When did you last do a worm count or worm?
Occasionally a pot belly can be a wormy pony.
Otherwise as said above, he needs to be moving and looking for food.

 

[Jxmxg]

He was wormed almost two weeks ago with equest pramox (reccomended to me by vet as we were unsure of his worming history since I only bought him a couple months ago) and I haven't seen any worms in his poo. His previous owner said he was up to date on wormong etc.. But I wanted to be sure.

He is not fed hard feeds just a power supplment and handful of chaff. He does get a carrot or apple each day also. X