I have a QH mare that I keep on hay only.  Due to having to change boarding stables twice this spring, we are having trouble getting her access to free choice hay.  I have her eat hay only as she gets hot on grain.  Her latest boarding facility wants to add hay stretcher or grain to her diet as she is slightly thin. 

 Important Note:  She is a 4.5 on the body conditioning scale and her vet says he likes horses to be at that score - he is very happy with her weight

My question is this:  can hay stretcher make her hot?  She gets 5-6 flakes a hay a day and pasture turn out all day every 3rd day right now. (14.2, and approx 830lb mare)  The woman who owns the barn would like her to gain 100 or so pounds to "look better".  She has no physical problems and is a joy to ride right now.  In the past, on grain, she has been like a bronc horse - just insane - its not good for her (injuries) or me.  I'd love to see a little more weight on her - but not at the risk of her going cuckoo.  I'd rather she be healthy, happy and be able to barely see 4-5 ribs, than risk her injuring herself because she got hot.

 Would appreciate any thoughts.  Thanks in advance.

I think the barn manager doesn't know what a healthy horse looks like. For her to want to put more than 12% EXCESS weight on your mare is insane. Believe your vet: he knows what excess weight does to horses--and people--and if he's happy with her weight as it is now, don't change anything. I don't know what a hay stretcher is, but that doesn't matter. Your mare is doing fine as she is. If you can just barely see some ribs, that's a good weight. Some horses, just like people, are naturally slender, and if you try to fatten her up you're doing her a disservice. Adding more muscle is different than adding more fat, and just adding fat--like the other woman wants to do-- does nothing for her soundness or quality of life. I say you should stick to your better judgment. 

 Even though I agree that it doesn't seem like your horse needs anymore weight, I do know that hay strecher does NOT make a horse hot.  My horse gets two guarts of hay strecher a day because he will get hot on beet pulp.  It helps him get the calories that he needs, and he is much more calm when getting that instead of beet pulp or grain!

Thank you both!  You helped me a lot.  I didn't want to add anything to her feed this summer, but should she need something as we go into fall/winter it's nice to know the hay stretcher wont make her hot. 

I'm a little worried about the fall/winter - before she had free access all day in the colder weather and did good, now with that not an option I'm hoping she'll be just as good this winter. (Seems weird to be thinking about winter on the first day of summer!!)

Trust your vet, and as far as hay stretcher contributing to any "hot" horse, I'd also speak w/the vet about feeding it to her, especially since it sounds like she's able to consume/digest the hay.  My experiences w/hay stretcher (Blue Seals), has been very positive, however, my old QH has lost his side teeth and is unable to chew the hay anymore.  I had much difficulty getting weight on him until the hay stretcher.  Still I contacted my vet for confirmation.  Make sure the vet is aware of amounts of feed/hay she's given - go from there, good luck!

good, sound advice from Deew.  As with a lot of things concerning horses (starting to sound like a broken record!); how much thinner or heavier a horse should be is very controversial, but like you said if she's at a good point on the condition scale and her vet approves and most of all she's happy, then sounds like all is good. 

You are right however to be concerned about the winter if she will no longer have access to free choice hay, but then again like was suggested, your vet will have the best advice.  Let us know!

I also agree with everyone about your mare.  I would listen to your vet before the barn manager.  Some people think horses should be heavier so they look "healthy" when in fact, adding weight unneccesarily could lead to health issues in the future.  As for the hay stretcher, we use it at the barn I work at.  We use it mainly in the winter where the horses aren't getting pasture like they do in the summer.  We only have 2 horses that get it year-round, Spicey who is 40 years old (acts 10!) because she quids her hay and Trooper, our latest rescue, who does need to gain weight.  We also feed grain, but we've never had a "hot" horse due to grain, what kind of grain were you feeding her?