Easy Keeper Mare lost weight , why?

Question
Hi!
I bought a very nice A/O Hunter mare in Febuary, upon purchasing her she was still on stall rest from a hoof injury (since healed). She is an easy keeper eating literally one handfull of grain twice daily with near free choice hay. When we got her she was in very good hefty body condition, she had a lovely neck, nice crest and was round in her barrel, shoulder and rump. She is being boarded. About a month and a half ago I noticed she had lost some weight which was odd because she was on the same amount of food from when we purchased her, she was not in work either and was just sitting around like she had been so it wasnt lack of muscle. We upped her to one small coffee can of Safechoice which is about 1/2 a scoop. I didnt want to up grain because she really didnt need it before. I think she was not being given enough hay at the boarding barn and they didnt give her the corn oil she was supposed to be on, could this have all made her loose weight? She is not "skinny" but sometimes when she moves you see her ribs and her neck is much thinner. Also she has started dropping grain, tho I don't think that it should matter (the vet said her teeth are fine she is just messy and a busy buddy who sticks her mouth out of her stall when eating) because she wasnt on much grain to begin with. Also the paddocks are small and dry lots and they did not clean them so I was afraid for worms even tho I worm every 6-8 weeks. We have just moved her but want her back the way she was! I have pictures of then and now if anyone wants them. I think she should put on weight with more hay and the corn oil but im just worried!

Answer
I entirely understand your concern.  Without knowing more specifics, your question may best be suited for your veterinarian.  However, it seems to me that her lack of work has altered her metabolism.  Also keep in mind how much different environments can influence a horse's digestion.  Finally, I think what has happened was a change in the quality of hay.  You are right not to up her grain very much.  Perhaps what she needs is a better alfalfa in combination with what she is on now.  Ultimately you must remember to gradually change her diet as you know colic is a concern.  My advice to you is to talk with the barn manager from where you purchased her, the barn manager from where she was last boarded, and who you currently buy your hay from.  Try to find out about the hay quality and maturity.  I have pulled a few excellent articles that will help you identify the right hay to feed your mare for her current situation.  Once you have investigated her feed quality and have read these articles, ask your veterinarian what he/she would suggest based on your findings.  Horses in light work definitely have different feed requirements than horses in heavy work.  Often times boarding barns may not be able to maintain a variety of feed for all their horses, and will simply have one feed "fits all" supply.  

If however you discover that the hay she has had has been roughly the same in content and you are still stumped, consider a thorough exam from your veterinarian.  Sometimes a blood panel can help to quickly evaluate your horses needs.

ONLINE NUTRITION ARTICLES:

http://alfalfa.ucdavis.edu/Symposium/1998/Evaluating%20Hay%20for%20Horses.htm

http://ohioline.osu.edu/b762/b762_7.html

http://www.triplecrownfeed.com/newsforagealternatives.php

http://www.completerider.com/nutrition.htm

Please feel free to ask a follow up question if you need to!