Hi, Kate, and welcome to the list!  You will get a more complete answer in due course; and, as Cheryl says, we can answer more fully if we know more about your mare (age, breed, diet etc) and where you are.   In the meantime, I have a couple of suggestions.

First of all, what is not fed to an IR horse is more important than what is fed.  Purina Enrich Plus (if that is what you are using) would blow the feet off of any IR horse I know if fed at more than a pinch a day. Sorry! We aim for less than 10% ESC plus starch for all feeds; and I know from personal experience that feeding more than half a pound of a feed of 4.5% ESC and 4.5% starch will cause foot pain (too much starch). No oats, carrots, apples, pasture. The analysis for the Enrich Plus shows 10% sugars and 5% starch; not enough copper and zinc; no iron listed; no ingredients listed that I could find on the website.

http://www.purinamills.com/horse-feed/products/enrich-plus-ration-balancing-feed/

You can safely implement the Temporary Emergency Diet: soak the hay for one hour in cold water, or 30 minutes in hot water; drain the water where the horses can't get at it. (I used to drain mine into my gardens). Add 2,000 IU Vitamin E per 1,000 lb horse, plus 3/4 cup ground, stabilized flax, 1 tablespoon salt, and 1 tsp magnesium oxide per 1,000 lb horse.  To get these supplements into your horse, use an IR-safe carrier; one of or any combination thereof: rinsed/soaked/rinsed beet pulp; soy hull pellets; Ontario Dehy Timothy Balance Cubes; Nuzu Stabul 1; LMF Low NSC; or similar.  Please stop the Purina Enrich, or just use it as a scant handful for a taste-tempter.

It is totally reasonable to get a regional hay balance.  You can contact your agriculture extension officer; or let us know where you are and we can maybe direct you in the right direction.  

Safe and useful mineral balance supps in the meantime: Uckele U-balance Foundation (this one is always good) 

http://equine.uckele.com/u-balance-foundation.html

California Trace Plus (again, always good):

http://californiatrace.com/catraceplus.html

These are great mineral supplements, especially for trace minerals, but can't always balance the major minerals (calcium, phosphorus, magnesium) in your area; also, selenium and manganese will vary across the world and across soil types.But, until you can contact your regional network, either one of these will be good. We can also direct you to resources in Europe, the UK, and Australia/NZ.

This folder has a file that gives some ideas for hay storing and hay soaking:

https://groups.yahoo.com/neo/groups/EquineCushings/files/Hay%20Information/

Short synopsis of the above: your mare won't perish if fed only soaked hay and salt for a few weeks, until you can organize the vitamin E, flax,magnesium and a safe supplement and carrier. (salt is important to make sure she drinks enough water to prevent impaction colic) You can shake the salt onto her hay.  She may, however, suffer laminitis if on pasture, or fed the Purina or other high starch/sugar feeds.

Hope this helps!

PS - dealing with IR becomes second nature after a relatively short time, and steep learning curve. If you can do it before laminitis strikes, you will be way ahead of the game.

Jaini (BVSc),Merlin,Maggie,Gypsy

https://groups.yahoo.com/neo/ groups/ECHistory/files/Jaini% 20Clougher%2C%20Smithers%20BC/