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Hives - could it be the bedding?

From: X

Dear Jessica:

By now, you probably skip the first few sentences of e-mails, which are inevitably accolades and expressions of gratitude for the wonderful service you provide, but in spite of the redundancy, I have to tell you thank you and express my wonder at your scope of knowledge, and its accuracy! Your advice nearly always mirrors the advice that I receive from my vet, farrier, and trainer, but comes with the added benefit of being given with the "whys" and "hows" -- I truly feel like I learn so much from your archives that benefits my horse!

I've searched your archives for a response regarding hives, but didn't find anything. I hope you can help.

My five year old Arabian gelding, Khodi, has had chronic mild hives for the past few months. The hives are small -- not really palpable on the skin, but the hair is raised throughout his neck, shoulders and withers. (We live in Southern California, and this winter has been extremely mild -- no rain to speak of, no fires, just lots of sunshine and warm weather.)

My vet said the hives appear to be topical, and too mild to treat. He suggested that Khodi might be allergic to his pine shavings. I have located shavings that are a mixture of bass wood, fir, and a small amount of pine, and will replace his 100% pine shavings with the mixture, in the hopes that it will help.

However, he's had shavings (same brand) his entire life, and has never demonstrated any allergic reaction, so I'm a bit confused as to why it might suddenly cause hives.

Therefore, I have two questions. First, have you heard of a horse suddenly developing an allergy to something he's been exposed to for quite some time?

Second, isn't it true that most hives are caused by inhaled allergens? Khodi lives in a stall with turnout, and is also turned out to pasture for a few hours per day. He is ridden 3-4 days per week, and I go out on his "off" days in the evening to groom him and play with him. He's been in this stall for 16 months, with basically the same routine. He doesn't have any respiratory problems.

He is fed grass hay twice a day, and 2-3 pounds of a mixture of oat-based supplement (Kruse Elite Performance) and alfalfa/timothy pellets, with a few cubes of alfalfa/timothy hay thrown in for good measure, which is moistened. He also gets electrolytes and probiotics with his supplements.

The only change in his routine in the past few months has been the addition of Strongid-C daily (from October 24 through January 4) and the probiotics (October 24 through the present). I added these following a worm colic episode on October 24, at the advice of my vet (I thought I had Khodi on an ideal worming program, which I did, except that I gave the wormers to my trainer to administer, and apparently Khodi was not wormed for several months, but my trainer's horses were, at my expense!). He is once again slick, shiny and healthy, with the exception of the hives. (I also bought "new" used reins, which occurs to me as I'm writing this that perhaps they were treated with something he's allergic to??) He hasn't been exposed to anything different in the way of shampoo, fly spray, etc., nor does he share his brushes or tack with any other horse.

Have you encountered such a situation? Does anything in his routine sound like it could be causing mild chronic hives? If so, can you suggest anything in the way of treatment (environmental changes or medication)? Also, what are the risks of not controlling the hives? Thus far, they don't seem to bother him at all, but naturally I want him to be completely healthy, and am concerned about this new development.

Thank you very much for your help!

[Please withhold my name. Thank you.]

Hi - and your new name is "X". I hope you like it. I don't skip any part of HORSE-SENSE e-mails, and I thank you for your kind words. ;-)

Yes, this is something I've seen before - and I'll bet that your veterinarian has, too. You've described the situation very clearly and thoroughly, and in the absence of any other obvious cause, I think that your vet is right, and your horse's bedding is indeed the most likely culprit here. I can't offer you the authoritative viewpoint of a vet, but I can give you an educated layperson's viewpoint, and then suggest that you discuss this letter with your vet.

Wood shavings make nice bedding, but we need to be careful about just what kind of wood is involved. Pine and cedar shavings smell nice to us, so we like to use them for our horses' bedding, but this isn't a good idea. (By the way, they're not good for your hamster or guinea pig either, and good pet shops won't sell them to you). The shavings smell nice to us because of the scented oils (aromatic hydrocarbons) they contain - but those oils are irritants, and can cause allergic reactions, including rhinitis, conjunctivitis, and even asthma in both humans and animals. Just because a wood product is "natural" doesn't mean it's guaranteed to be safe.

Most of the studies on the effects of wood hydrocarbons on the body have been done on humans, because many humans who work with wood are exposed to those hydrocarbons for eight hours every day, five days a week. If your hamster's cage or your horse's stall is bedded with cedar or pine chips, the animal is exposed for much longer - possibly as much as sixteen to twenty-three hours a day, seven days a week. You may need to look for shavings from wood that doesn't contain volatile aromatic hydrocarbons, or for some other type of bedding such as straw, shredded paper, peat moss, or hemp. It's also possible to find wood chips or shavings from safer woods - or to find other wood-derived bedding products. Some manufacturers are offering processed wood chips and shavings that have been been milled to removee the resins and oils. What's left after the processing is sterile wood fiber - nothing else. "Woody Pet", for example, is a pet (including horse) bedding advertised as being completely free from aromatic hydrocarbons.

There are other possibilities, of course. Food allergies do occur in horses, and those allergies can result in hives. It's not easy to figure this out even if your horse lives in your back yard, and it's extremely difficult if your horse lives in a boarding stable. In a barn where many different feeds are in use, your horse could have an allergic reaction to his own feed - or he could have an allergic reaction to something that is being fed to his neighbour, or the horse four stalls down, or the one across the aisle...

Some horses can have an allergic reaction to drugs - including the common ones that seem to be in every horse-owner's collection: bute, banamine, procaine penicillin, and acepromazine.

Almost anything, in fact, can provoke an allergic reaction, especially if the horse (or human) is under stress, or has been under stress, and has an immune system that is functioning at a lower level than usual.

Under the circumstances you've described, bedding would be my first suspect, but you DO need to find out what is causing the problem. Hives are rarely a reaction to a single event - it's not the single insect sting or the single night in a stall with the wrong bedding or the one scoop of new feed that causes hives; they appear when your horse is having an allergic reaction to something he has ALREADY been exposed to.... such as, quite possibly, his bedding.

If changing the bedding doesn't eliminate the hives, or if the hives become more severe, you might want to talk to your vet about performing an intradermal skin test.

Since your horse's hives are mild, you shouldn't panic - but you should be aware of just how dangerous severe hives can be. If you find more and bigger hives on your horse, your vet will need to be told this immediately. If your horse needs treatment, your veterinarian has quite a few drugs to choose from: corticosteroids, antihistamines and non-steroidal anti-inflammatories, singly or in combination. In addition to more severe hives, there are other things you should watch for. A really severe allergic reaction can turn into anaphylaxis, which would definitely qualify as a red-alert emergency. If you come to the barn and find your horse breathing much too fast, wheezing, or flaring his nostrils in an effort to get more air, or if you find him acting extremely twitchy and nervous, you should talk to your vet immediately.

For now, focus on management rather than medicine. Change your horse's bedding, get him outdoors as much as possible, keep a close eye on him, and stay in touch with your vet. Clean your reins - just in case they were covered with flyspray or some other product to which your horse might react.

Try to arrange as much turnout time for your horse as you can - 24/7 if possible. When you ride, if you can ride outdoors rather than indoors, do so - you'll be getting away from the dust produced by bedding and feed.

Just a note: unless your horse is working hard and sweating profusely, you can leave the electrolytes out of his daily feed. They're helpful ONLY if a horse is sweating enough to create a significant loss of mineral salts. Save your money - you may need it for your horse's new bedding!


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