Dieting Appy Mare

They both have small mesh hay nets which I secure inside the half barrels. And if I leave them together, even far apart, she is ruthless about chasing the gelding off. He needed to keep weight or even gain some, so to be fair to him I had to separate them.
And over here supplements are very essential. The soil (and thus the hay which grows from it) is basically an entisol, which means it is very very young and devoid of organic matter and nutrients. And she literally gets a palms full of the rolled oats. I think I even counted about 20 oats last night. And even if they are just making expensive manure, I compost it thoroughly and use it on the veggie garden, so the more nutrients the better!
As she is getting a hang of the smhn I am introducing more hay so she can nibble throughout the day. Again, she is NOT my mare so I do have to honor the requests of her owner and bounce ideas off of her. Her owner is quite adamant that she only needs 1 ton of hay a year...

Maybe her owner doesn't understand how much hay a horse needs- she should be getting at least 1.5% of her ideal body weight in feed daily. 1 ton of hay a year is about a quarter of what a small full sized horse needs (based on an average of 20 lbs/day). Maybe she got away with 1 ton of hay a year when her horse was on pasture in the valley, but if she's essentially in a dry lot now, she's going to need a lot more!

Verona, I agree. I have been trying to educate her and gently persuade her that Central Oregon is a totally different ball game in horse keeping than the Willamette Valley was.
And I live by the 1.5% rule! Right now she is getting just over that in hay, and a seriously negligible amount of oats to get her to gobble up her vitamins. And she is indeed losing weight, and at a good rate now. The first week, as I mentioned before, was just a bit shocking, and looking back, perhaps I could have eased her into the diet even more slowly than I did.
I truly think that for now her owner and I have come to a good compromise where the mare is on her way to health.

Plus, I bought enough hay for both horses how I like to feed for the year, so there is no risk of her going hungry in my backyard!

Whew, good thing you're there to keep her healthy while her owner adjusts to the new environment

Its good her owner has someone like you to help! Keep up the the good work :)