Horse weight issues!!

[petite-girle]

I have 3 horses all kept in the same field. I have a 15.1hh ish 3 year old warmblood who is on the slim side, (but still a healthy weight) I have a 12.2hh yearling filly that is just right weightwise and I have a 12.2hh yearling filly that is without doubt FAT!! So it seems there's barely enough grass for my warmblood, and way too much for one of my filly's even though the field is pretty bald. I have sectioned my 'fat' filly before and she becomes very distressed, stands there constantly calling even though she is still with the others.
It just is strange how different each horse is weightwise on the same grass.
(Obviously my gelding is bigger then the girls mind you!!) And it seems very difficult to get my 'fat' filly to slim down with only access to my one field.

 

[Meowy Catkin]

Have you tried putting a grazing muzzle on your filly for a few hours a day to restrict her grass without sectioning her off from the others?

 

[Paigeous]

Hmm this does sound a bit difficult. I have a similar issue. I have a 14.1hh 9yo Welsh cross & a 15.2/15.3hh 2yo Irish Sport Horse. They both eat quite a lot but obviously I try not to let the 2yo put on weight due to the problems this can cause with growth, joints, etc (I'm sure you know what I mean) & my Welsh is supposed to be quite round but doesn't get much work atm so has to be kept trim through diet.
They both put on weight quite easily & eat the grass down in their field really quickly. I split my 2 acre field into 4 equal-ish paddocks and rotate them approx every 2 weeks, depending on how the grass holds out. So each paddock gets 6 weeks growth before they come back into it.
It's working quite well for me. They put on a bit of weight in the first couple of days but once the grass gets quite sparse, they even out. I leave them in each paddock until there's almost nothing left so that they fully lose the bulge they put on in those couple of days & then move them again. Perhaps something like this may work?
You could also let them have very little grass but take the slim ones out & give them feed to top them up & see if the fat one loses some weight at the same time?
And it may be possible to lunge some of the weight off the fat one. The amount of lunging you do within a day should not be a lot for a yearling but even ten minutes of walking as often as you can do it could make a difference. I started lunging my ISH before she turned 2 & I use it to keep the pounds off her a bit when they move paddocks.
Hope this helps