Sound soo much like my horse! (who is also 3/4 tb)

This is the advice i got from my vet-

she needs at least two feeds a day, preferably 3 with a high fibre content. Make sure she is well rugged and has plenty of hay, if she's out during the day and there's not much grass give her a bucket of redigrass or a bale of hay.

My horse is now fed allen and page weight gain mix (1scoop) showshine mollichaff (1scoop) basic mix from local feed store (1/2 scoop) with two sleeves of hay during the night (but our grass is also good) and i also add garlic powder. She's fed in in the morning and at night

sugar beet is good as it keeps them warm too (but i have found i haven't needed it yet!)

last yr she looked a state but she looks stunning now!

you could try grass nuts, you soak them and they are good for bulking horses out, very cheap too :)

hi i'm havin the same problem with my irish cob who is 15 she been wormed, teeth checked, vet even been out and she 2 scoops of ossi chaff , 1 scoop of fast fibre soaked in 1 1/2 scoops of water ( fast fibre expand when u add water to it ) 1  cup of spillers feed balancer and 1 scoop of speedi beet and veg oil and she has this twice a day  and she still doesn't put wait around the flanks area :-(