This summer I'm leasing a horse from my University Polo Club, and am boarding her at a farm with a grass-only diet for the horses. Because the pasture is big and had lots of grass, this was working fine for the first half of the summer, and all 3 of the horses there stayed at a nice healthy weight with access the big pasture (there's a separate smaller one with less grass) for approx 6 hours a day - my horse even was a bit low on weight when she came, but gained quickly and soon looked healthy.

However, the rain has now essentially stopped coming, and the entire pasture has turned brown and is as good as dead. When Ebony, my horse, started losing weight at a rate that concerned me, the horses were given all day access to make up for the lack of grass. I also started adding some corn and soybean oil to the black oil sunflower seeds I was already giving her every time I came out (almost every single day, but not always), and giving her hay when I could. However, she's a really picky eater and the only way I can get her to eat hay is to cut her off from the other horses (she's at the bottom of the pecking order) in the small no-grass pasture and leave her in there for four hours, during which time she'll get through almost a flake of hay, maybe. This cutting-off-to-get-hay system will only work if I'm the one who does it - the barn owner won't - which makes it hard to do consistently because I need to be at the barn the whole time (it's too far to drive to twice in a day).

I've managed to get enough hay and other food in her (I also would just take her out and graze her on any green grass I could find instead of riding her) that she's stop losing weight and has even appeared to gain some back, but not as much as I'd like. Watering the pasture isn't an option; it's too big and bc these horses are on a farm the actual crops get priority as far as watering goes. Because this horse is not mine and I give her back to the Polo Club in 2 months and I work a minimun wage job and am a college student, I don't want to spend a ton of money on her, but I also don't want her to be unhealthy or malnourished, and would like both to be able to ride her (I felt I couldn't with how fast she was losing weight for awhile) and send her back in good health.

The big question: is there (decently cheap) supplements - grain or natural or what have you - I can give her to make up for what she's no longer getting from the grass, and/or is there anything else I can do to help her gain back some weight? Is there any vitamin/substance I should focus on getting into her to keep her healthy, or should I just focus on gaining weight? Any supplement/grain would be likely incorporated into the BOSS/corn/soybean oil mixture I give her almost every day. This is the first time a horse's weight has been left to me to take care of, rather than the barn owner adjusting grain/hay, and the first time I've had a horse on a grass-only diet, so I'm unsure of what to do now that the rain has forsaken us. :/ Any ideas and suggestions would be greatly appreciated! 

(Sorry this is so long, thanks to any that read and will respond in advance, I am very grateful. :] )

She needs access to quality free choice hay... this means as much as she can eat and probably a ration balancer like Grow N Win.  This horse is an OTTB so will lose weight at the drop of a hat if not getting enough hay or pasture.  Always, always feed them as much hay as they will eat then add a concentrate if needed. 

If there is no grass someone needs to be thowing hay out for the horses while they are out and they need hay while they're in too.  They need hay in front of them 24/7 period.  This cannot be stressed enough.

 I agree with free choice hay, free choice hay is what keeps my TB at a good weight during the NH winters when he's living outside with little to no blanketing.

I'm not sure how well it works having no experience with it (or if you can even get it where you are located) but Blue Seal has come out with something called ecube.  They say it's "A Forage-Based Total Mixed Ration for Your Horse.  The soft, easy-to-chew TMR cube is designed to be fed 24/7 --- that's continuously throughout the day as the only feed source.  No other hay or grain necessary."  Here's the linke to the product: http://www.blueseal.com/equine/ecube.php

Again I have no experience with it and have no idea if it's available for you as I believe Blue Seal is an east coast company, but I know they're owned by Kent Nutrition Group.

I was assuming she was the horse that's in your signature which says... OTTB.

She's going to need more than 3 flakes a day.  If you put her hay in a small hole hay net it will last longer and there will be less waste.  I would put at much as you could fit in it everyday and since you get the hay for free you don't have to worry about cost. 

What breed is she and what's her workload?  You could just add a ration balancer if you're concerned about her keeping weight.  A couple of my favorites are Buckeye Grow N Win, Buckeye Ultimate Finish (high fat) and Legends Omega Plus (also high fat). 

But still....hay first, then a concentrate if you need it.

 It sounds to me like your more concerned about ensuring she gets the proper nutrients and not so much about getting her to put on weight but to just make sure she maintains her weight and ensure that she gets all of her nutrients.

If that's the case maybe try a mineral block before going to grain, they're cheaper than grain and they are free choice so you don't have to get there at specific times in the day.  Just remember to get one from a feed store near where you're keeping your horse (the closer the better) feed companies formulate their mineral blocks specificly for different areas (for example NH is notorious for being deficient in Selenium (selenium defficiency in cattle was originally called Carroll County Disease after the county it was discovered in) so mineral blocks here have more Selenium in them than other parts of the country)

Don't get the plain white ones as those are just salt, I usually buy my horses a trace mineral block (big block) they're usually brown and then for their run in shed I buy them 2 little stall ones (they love the little carrot flavored ones).

I would highly recommend trying to purchase ADM feeds.  I bought an Appaloosa two months ago, and although he looked good in the picture on the website, when I got there he was very skinny and just rough in general.  After only two months, his weight is almost completely back to where it should be and he is absolutely gorgeous.  And during thsoe two months, I have been working him fairly hard to get him ready to resell.  Not to mention that his teeth aren't the greatest.  I fed him 1 lb. of MoorGLO, 1 oz. of GroSTRONG minerals (this particular feed doesn't contain minerals/vitamins), and free choice hay (no grass).  It's very inexpensive, because it's concentrated so you can feed less of it.  That way, the horse has room to fill his stomach with more of what he needs--forage.  I also have my other horses on ADM feeds--one on MoorGLO, one on PowerGLO (which is more expensive, but does contain the vitamins/minerals)--and they are looking better than they ever did. The feeds are based on forage, so it's designed with the horse's digestive tract in mind.

I've attached the before and after pictures of the App to show you the difference.

Good luck with your mare!!!

"Chief" the day after I brought him home

Chief two months later