I have a 15 year old rescue palomino quarter horse mare I've been taking care of since Nov. She has never missed a meal & has gained weight beautifully. She has been in the same dry lot during the day and stabled on straw in my barn at night. Monday she had a sore develop on the back of her forearm about the size of a half dollar. The next day she had one on her thigh. I first thought she was scraping on something so investigated the premises and found nothing. By that night she had a large one 6" round develop near her flank. They look like a dirty spot on her coat then start weeping. The next morning she had 5 more about 2-3" round on her thigh & gaskin. I took her to the vet & he has never seen anything like it. He shaved the hair off & thought it looked like something caustic did it but there is nothing in her pen that should be caustic. He gave me 1% silver sulfadiazine cream to put on it. They weep but have no puss, seem very tender to touch. The weird part is they are only appearing on one side of her body. The only thing I've done different is worm her 3 days before the break out & a new round bale of grass/alfalfa mix was added the day before. I'd been feeding small squares of the same mix. I've read about photosensitivity in light colored horses due to alfalfa & am wondering if this could possibly be the cause??? We haven't had much sun though & she still has a heavy coat on although she's been shedding like crazy since Dec. No new sores have appeared since Thursday. I have another horse that shares the same lot & so far she is fine. I'm just wondering if anyone has any ideas or has dealt with the same problem. Thanks for any input.

When I fed tonight more spots have developed on her other side. After researching more I'm thinking maybe hives?? When I rub her belly it feels lumpy, some larger than others. She'd been given penicillin for a respiratory infection a few days ago, she's had it before with no reaction but I've read where they may have a reaction if it goes directly in the bloodstream. I plan to call the vet in the morning to see if there is something to give her relief from the itching.

A few thoughts. The first is Ring Worm- but your vet should be able to recognize that. You can treat it topically with Ivermectin applied on as you would any other ointment.
The other allergies, either injested any feed stuff[hay/grass/feed/supplements...] anything that goes in her mouth. Or topical, new bedding, no bedding,fly spray different shampoo.
Not seeing her can't say for sure.
But similar, got a very skinny pony from auction, had a beautiful haircoat[although dull] Brought him along slowly with hay first,wormed him. Spring starts grass comes in starts {shedding?} Try to help it along by brushing-all hair comes out. NAKED
Is allergic to proteins- can ,maintain on whole oats and over the counter antihistimines.
Did your vet do a skin scrape when he shaved/cleaned the area. Would probably have @ least that done.

Thanks for the reply. I know its not ringworm, have seen it before. This morning she has more spots, the oldest are drying up though. The worst are behind her forearms & seem very tender when I put the salve on. They are really weepy, running to the hoof. The lumps on her belly seem to have gone down some so hopefully it is running its course. She has no sores (so far) on her face, neck, barrel or back. All are from the mid-thigh down. I haven't changed feed, bedding, etc. The new bale of hay could be it but she hasn't had access to it since I'm keeping her in the barn to try to keep her as clean as possible. I've talked to several other horse owners & no one has seen anything like this. She is still eating everything I put in front of her, seems content & is being a trouper about cleaning & salve application. The vet didn't do a skin scrape & he was closed today when I tried to call. I'm getting to where I dread going to the barn.......she was just getting so pretty.

Lets hope its not, but worse case senerio is the hereditary disease known as HERDA. I have never dealt with it, but have known of a few horses with it.
Being an auction horse and possibly a QH, might be to rare for your vet or friends to know about.
horsecity.com/stories/031204/hea_herda_KT.shtml
bringinglighttohypp.org/HERDA.html
thehorse.com/images/content/hc_herda/hc_herda2.html

If it is hives and they are making her itchy then the possiblity of her rubing until they are open wounds is possible. A little bute twice a day with a shot of steriods, and maybe some Hydroxyzine from you vet would benefit her. Keeping her in the stall is good but I would strip the stall and put clean and/or different bedding in. The silver sulfadiazine cream is good for those types of wounds. Also it is burn cream so great to keep around the barn/house for horses/humans. IT is a very soothing cream. You may want to get a little betadine/povidine scrub (soap) and wash the wounds onces a day, this is a surgical disinfectant, If no feed store is open you can sometimes get it a walgreens. THe scrub would be best but if they dont have it the solution will work. I would wash the sores once a day gently and then apply you Silver Sulfa cream.

In general the reaction seen when a horse gets penicillin in the bloodstream is very noticalbe they become very overly sensitive, the easiest way to describe it is they freak out. I have been around two horse that when given a shot of penecillin the needle must have hit a small blood vessel on the way out and the horse began to freak out immediatlely. I have never seen one get hives though.

IF she is still getting more of them I would call you vet on Monday (if you cant get someone out today) and have him recheck her maybe draw some blood and run a panel, and maybe see if it would be a good idea to culture swab a couple of them and send them off to the lab and see if they show anything.

Hopefully it is just as simple as hives and some drugs will do the trick. Let us know what happens, good luck.

By 4-30-08 all the hives (I guess that's what they were!) were gone. She didn't lose any hair where they were so that is a good thing. Still a mystery what caused them. Hope they don't come back!!!