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My mare is on a low carb feed - gets about 2 - 3 cups a day. This feed is primarily Soy Bean Hulls. Blue Seal Carb-Guard.

When she's in season for the first couple of days she's horrible - to the point I don't ride her. On the ground she's good - but, get that saddle on and wahoo she is a bit crazy. In her crazy state she also sweats horribly. I'm wondering if the Soy is causing her heat cycle to be more intense.

Since I really haven't had her on another feed, except when she was pregnant I don't have any experience to say it is the feed.
I've done a little on-line research and could not find anything definitive on soy affecting mares in a negative way. On the COTH board, I saw a few comments that come posters felt it definitely affected both mares and geldings.

I want the best nutrition for her and a feed that doesn't make her hot (sugar).

My appy gelding was colicky and miserable with anything soy in his diet. When he came to me, he was eating sweet feed. I turned my nose up at that and put him on a "better" pelleted feed... then spent several months trying to work out what was wrong with him, until I had one of those 3am lightbulb moments...

So yes, I do believe it's an ingredient to use with caution on some horses. Most horses can chow down on it happily with no problems.

You've got nothing to lose by trying to eliminate it and seeing what happens.

We went to 2 parts oats, 1 part alfalfa pellets, 1 part rice bran meal, and a multivitamin, (and hay, of course) and he's eaten that happily for the past 10 years with no ill effects. Now he's no longer in real work, he gets a bare minimum, but it always kept him in good condition and not stupid when he was in heavy work, too.

If you do eliminate it, watch out for supplements and horse cookies and stuff like that, as well. It's all over the place.

From what I can find, studies show there's really no definitive correlation, but there's enough anecdotal commentary that it gives pause for thought.

Soy=estrogen...so...

My mare had some wicked heat cycles for a while. Even on the ground it was a major fight to keep her from screaming and running back to the herd. Riding was out of the question as it was a mental disaster and she was CONSTANTLY squirting...at geldings, stall walls, posts, whatever she could rub against. I had an agreement with her that I would leave her alone for the first two days of her cycle and any other day she would be a decent princess.

I did notice a difference when I switched her from Safe Choice and Tribute (heavy soy) to Triple Crown Senior, which was more fiber based. If that was truly the culprit, I don't know.

Thanks for the replies

What's funny is I have never seen my mare squirt, wink, or even take any notice of geldings when she's in season. It seems to effect her more mentally (like no concentration) and somewhat physically. Possibly when I put the saddle on her it causes her pain that's why she is nuts on the lunge.

I was looking at a Vit E supplement and it has soybean oil in it - so, I am watching for hidden SB oil. I went with Smartpak natural Vit E supplement - no SB in it....

A friend said since the feed is Soy Bean Hulls - during processing the oil is extracted from the bean - so it may not have any estrogen/hormone effect. Wonder if there is any truth to that?

How old is this mare?

Moutaineer - She is 7 and had a foal last May. As far as I know it was her only foal - but, I can't be 100% sure of that.

Another thing that happens when she's in season is that her udders and teets get a bit larger. Her udders have never totally shrunken up. I did have the vet check her for a low grade mastitis and he said - no, she's fine.

I do wonder If the soy in her diet is affecting her udders.

One thing you could try is magnesium supplement. I like MagRestore and have had very good results helping a horse be more comfortable and relaxed. It's usually see results within a week of trying it.
or, just remove the soy feed for a few weeks and give only alfalfa pellets and hay and see if there is a difference. When I've been suspicious that something I'm feeding is bothering my horse, once I remove the offending food, I see a change within a couple weeks.

Most mares who have had a foal retain a small bag. ( udder) . Just as human breasts enlarge and become sensitive, during natural hormone cycle, so do animal udders . It is not abnormal.

Chisamba - I have looked at a few other mares udder area that have had 1 foal and they are a lot more shrunken up than my mares. That's what started my worrying process. But again, I guess each mare is different and if she had more than 1 foal that could be another reason...

Oh horses, does the worrying ever stop! ???

yes, it does differ with number of foals and from mare to mare. However, i cannot offer any tangible experience about horses becoming more mareish on soy based diets. On several breeding farms i was part of, soy was given to raise protien on a regular basis. on the one farm i was there for several years and the owner added soy, read something against it, and stopped for six months, and then changed her mind and started again, as the main trainer and horse handler there, with a rather large herd of mares, both worked and broodmares, i cannot say i noticed a particular difference in either breeding dynamic or attitude with the changes in diet.

that said, some horses are much more sensitive to things, and if i had a horse that was very upset in her cycle, i would try many things ( one at a time so i knew which worked) to see if i could help her. I mean PMS sucked for me, so if i thought i could help out a fellow creature to be less demonic when cycling, one way or another, i would try.

By the way i tried soy additives myself supposedly to help with menopause onset, and it did not a damned thing. so perhap I am biased but that was when Soy was considered the saviour of mankind, not the devil it is now touted to be