Wednesday, April 19, 2006

Headshaking Syndrome....Just the facts

(angelfire cartoons)

Just to set the record straight....this is a SYNDROME. That means it is a condition with multiple potential causes that has a unique set of symptoms. In this case the symptom is head shaking, this is either horizontal, vertical or rotary and frequently resembles a nervous twitch. Sometimes this is so uncontrollable that the behavior becomes almost manic and dangerous. Over the years many different causes have been attibuted to causing head shaking syndrome, including (1) ear mites (2) allergic rhinitis (3) ocular disease (4) Trigeminal neuritis (5) dental disease and (6) photic headshaking. One, from the fever swamps of the internet, links it to vaccines ( see my previous post about my thoughts on holistics) One older study noted that these horses were frequently over 8 years of age, Throughbred or Warm Blood, owned by 40+ year old women used for hunter/jumper or dressage. Additional studies have linked this to the time of year (seasonal) and most recently, to bright sunlight and body color ( chesnut with a large white blaze). All of this would tend to make you think that nobody knows what in the hell is going on......hence a "Syndrome". If you take a step back and look at this logically it might help. Horses like any animal can shake their head for many,many reasons. I frequently do it when talking to some of my clients, but thats for another post. When I was at Cornell I saw more of these than I could count and the cause usually went unconfirmed, however many responded to a change in location and frequently intra-nasal steriods, hhhmmmmm. That sure sounds like allergy doesn't it., but this doesnt explain all of them since others didn't respond. A great study done at UC Davis found a link between headshaking and photic sneezing in people ( sun sneezing). In this study it was shown that bright sunlight, usually in the spring, caused these horses to show headshaking and even go as far as to put their heads in open barrels or in the tail of another horse to shield them from the light. .These stimuli appear to hyperactivate the trigeminal nerve resulting in a nasal irritation. This is believed to be similar to the photic sneeze syndrome in humans. The light or sound-induced headshake is a more violent and irregular, snorting toss, compared to the more rhythmic traditional head bobbing or nodding seen as a classic stereotypy. The horse may appear to be trying to scratch its nose on a foreleg or even on the ground as it snorts, even going along at a Trot

. This form of headshaking almost always worsens under work, and immediately subsides as the animal is returned to the quiet and dark barn or rest, so is easily misinterpreted as a purely behavioral problem. In most cases, light-induced headshaking is seasonal, and will stop immediately when the eyes are covered or the area is darkened. Dark goggles or sun-blocking face masks may be all that is needed for some individuals.
Additionally , a group at Univ of Penn. blocked the trigeminal nerve ( in the face) and stopped many of the signs, however , surgical transection of the nerve caused some horses to rub their noses off....a significant complication.
To date there are several ways to treat these horse and most are medical. Cyproheptidine, an anti-histamine that effects serotonin levels has been the best, also the addition af a behavior modifiying drug Carbamizine has been shown to help. I think these work in cases where the cause is more photic in origin or behavioral ( like tick disorders in people) . If the cause is more allergic then the use of intra-nasal steriods ( Azmacort, 5-10 metered doses daily) seems to be effective. Others have used panty hose over the horses nose as well as the leather tongs/strips over the nose to eliminate these signs. I feel the ones that rub their noses on the riders and snort while riding are the harder ones to treat and frequently are the most violent while riding. If you have a horse that suffers from this I would encourage you to seek out someone with experience with this disorder or have your Veterinarian send me a note and I will forward some info on the subject. As always , use your mind and don't fall victim to those that are marketing /selling a cure-all. There isn't one, this problem has multiple causes and that means no one treatment will do it. You just might find yourself shaking your head wondering where all the money went.


Tarmi said...

I read the comments on the head shaking syndrome. My horse has a violent vertical head toss different from the head nodding or bobbing that he does on rare occasions. The vertical toss occurs between June and late August/early September mainly in heavily wooded areas and sometimes very overgrown fields with its height in July. It gets better on the dirt road and in the ring. It worsens on humid days. It starts to get better through August. My vet told my trainer to try a shot of acepromazine and if it helped there was a monthly shot he could get. I am not comfortable with this at all. What do you think?

Dr. Alan Weldon said...

The seasonality points to either photic head shaking or allergic rhinitis. The fact that it occurs more in wooded areas would suggest allergy. I would try a steroid inhaler (azmacort-triamcinolne) 30 min prior to riding and judge the results. A trigeminal nerve block may help in the diagnosis, good luck and let me know.
Doc Weldon

Erin said...

I know you posted this blog awhile back but I have owned a 17 hand headshaker for the past 8 years. He didn't exhibit the signs when I purchased him in the winter, but come spring he was full blown headshaking - vertical, horizontal, snapping his head like a bee stung his nose, etc. I tried everything - medicines, photic mask, nose stocking. Eight years later, we have our good days and our bad. Now, at 12 years old, he can be fine in the spring, but will shake his head for a few days in mid-December. It's definitely not as bad as it used to be. I never have a consistent year, though, and my shoulders are ruined from trying to ride through his headshaking (not smart, I know, but when everyone else's horse goes "normally" and yours doesn't, it makes you do crazy things). Despite this, I love my horse and, when he's not shaking his head, he goes beautifully. Thank you for posting this article. I try to read everything I can on headshaking, always hoping for a magic "cure." I do have a question - I'm thinking of relocating and hoping I can still afford to keep my horse. If I can't, how does one go about selling a horse with headshaking? Is it even possible? Or, if I move, could a location change cure his headshaking entirely?

Anonymous said...

Hi there, I am a new horse owner and very confused what to do with my 10 year old arab/paso fino mare. I have suspected for a couple of weeks that she might have ear mites. She is sensitive about having her ears touched and recently I can't even get a halter or fly mask on her because it is near her ears. She freaks out and I'm afraid she will stomp me. I got some medication for her but she wont let me near her ears to put it on. I tried to put it on a rag and rub it on her ears.. no way was she letting that happen. In desparation I finally sprayed the aerosol at her ear. She went berserk. I got some medicine in her ear but she has since rubbed her ear bald. Any advice????

Dr. Alan Weldon said...

It doesn't sound like a true head shaker since the ears seem to be so intensely involved. It is possible that there is a tick in the ear which will produce intense pain. I would suggest having your Veterinarian heavily sedate your horse and examine the ears. I had one once that i had to actually had to anesthetize to remove the tick. Let me know what you find.

sfletch said...

Hi I have a 17hh warmblood who was treated with steriods last yr and we changed all bedding soaked hay fly masks etc etc and it alll stopped so we put it down to allergy! Well he is off work now and the sun came out this w/e and I found him violently head shaking in the field and in the stable he goes to the back, after alot of research he is looking like a photic cause. I have come accross a product and was wandering if anyone has tried it or heard any feedback? Equiwinner performance patches they are formulated for a variety of things but seem to cure headshaking or so they say?

Anonymous said...

My 17 year old paint mare started violent, involuntary head shaking after recovering from a bout of colitis several years ago. There doesn't seem to be any rhyme or reason to why or when she has these extreme "twitches". It is not associated with sunlight, the time of year, or whether she is being ridden or not. Her teeth are floated on a regular basis and there is no problem with her ears. In 2006 & 2007, I sent her to a reining trainer and while in training the symptoms subsided to the point that I was able to show and win on her; but now that she is home and turned out to pasture, it is constant whether she is out to pasture, in a stall, or under saddle (or ridden bareback). The head tossing does vary in severity, but I can't identify the common denominator that intensifies the problem. I am afraid that I may have to put her down or sell her to slaughter if I can't find a way to relieve this problem. Does you have any advice that could protect this mare's happy home and future? Thanks for your help!

B Gasper said...

I wonder if my horse has been mis-diagnosed as having allergies - when in fact, he may have head shaking syndrome? Or both?
Symptoms - tests positive via blood test to several allergins. Does not respond to steroid pills. May respond to custom (Bio Med) allergy shots - have been giving them 3 years now. However, in the summer - June, July, August - sneezes non-stop, combined with tossing head in the air vertically. This sneezing/head throw improved when I changed his environment - moved to mountains.
Here's the really strange part: I get him out of his 1 acre pen outdoors wher he lives - he's sneezing - tossing head. Bring him into the barn, quickly brush him, tack him up and get the bridle on. I go out on a trail - for about 15 mins. And it dissipates much so, that I can return to the area (either indoor or outdoor) and ride him normally - very little sneezing / head throwing, if at all by the end of the ride. I put him back in his pen - after riding & he's at peace. He eats his hay (which he is allergic to some forms) and within 30 mins is back to sneezing head tossing. This does not happen Sept. thru April - in the winter he lives inside - turned out head tossing/sneezing - hay or no hay.
Allergy company says there are additional allergies in the summer - such that he may be reacting to a build up of allergies. I wonder.
I have researched this online - went to - a site hosted by Capstar - a homeopathic option for Headshaking Syndrome - so, they claim. Worth trying?
They claim horses build up allergies and reactions to shots. My horse was imported from NZ & for 2 years didn't display this symptom - he's had to have a TON of new shots here in the US, wonder if he's built up allergies to them?

Am quite puzzled and not sure where to turn.



Dr. Alan Weldon said...

I doesnt sound like allergies but it still could be. I assume he was on Prednisolone(steroid pill), this should have had some effect. The allergy testing for horses is very unreliable unless it is intra-dermal.
The seasonal nature could indicate photic sneezing (low serotonin levels). If this is the case you should treat him with cyproheptine to confirm. The "natural/homeo treatments are universally ineffective for this problem. It is totally unrelated to vaccines. There is a small cottage industry out there trying to condemn vaccines and blame them for just about any disorder. For now I would try Cyprohep or polarized goggles /fly mask and see what response you get from that.
My best
Doc Weldon

Joy said...

I too seem to have a Photic Headshaker... symptoms disappear at night and when blindfolded. Are you able to point me in the direction of a good polarized goggle, besides the God Awful looking Guardian Mask? A standard fly mask didn't block enough light to stop the headshaking... What about equine contact lenses?

Dr. Alan Weldon said...

The goggles do look a bit goofy. I think it would be possible to buy some polarized film and mount it into an area cut out of a fly mask.
Try this site

Also start the cyproheptidine as well.

Squishy said...

Interesting posts and comments made, but I have a question.
I have a 4 (near 5) gelding ottb, had him almost 9 months. First 6 months he was fine to lunge and be ridden (lightly, was mostly on spell). Approx 3 months ago we went for a bush ride, went past some pollen and it was like he had inhaled a flower - head shaking, stomping, violently tossing his head. He was fine by the time we got home.
Skip ahead to a month ago, he now does this in lunging - regardless of halter (rope/webbed) or bridle, UNLESS he has a flash on.
Teeth are checked, is not lunged with a saddle or roller, and has been lunged WITH saddle/roller - no diff. He does NOT do this ridden.

Any thoughts?

Jessica said...

I moved to Arizona from Virginia this June with my two TB geldings. The younger, a seven year old, bay with very small star, cut his forehead the day before we left Virginia. The vet says it was very superficial and sewed him up. Upon arriving in AZ we rode him a few times and lunged him and he seemed just fine. A few weeks later the vet here took out the stitches. While he was tranquilized she also floated his teeth, with power tools. When I went to ride him the next day he would not go on the bit, and began tossing his head. I switched bits several times, no change. I lunged him with and without a bit, then with and without a headstall, still head tossing. We had her back out and she did another $170 worth of dental (the first visit was over $300). We gave it some time, he got worse. An equine dentist with a great rep was in town, I had him look. He did not like the way the front teeth met, and some of the work on the back, and his did some corrections by hand (I'll never have dental done again any other way). An accupuncturist treated him at the same time. He was better, but not well. In early September I took him to a large clinic in Phoenix where they did $1300 worth of xrays of his head. Some inflamation around the earlier forehead wound and all around all of his teeth. They recommended Bute for two weeks to bring it down. We didn't see much improvement. It is not worse in light, it is just the same in indoor arena. Finally, after much research, I decided to start with the cheapest 'fixes' and work my way up. I bought a nose net and he is 90% better. I would like to work with a vet here to see if we can get it to 100%. I don't know that the initial dental set it off, or the move to Arizona, or what. The horse had just won his division in beginner horse trials in VA before I left, with a great dressage round, so obviously wasn't having issues then. What would you recommend my next steps be?

Anonymous said...

I live in UK and have a horse which started head shaking this year in May and continues to do so now in October. I have consulted the vet and tried: Guardian mask; nosenet/tights, Piriton, Cyproheptadine, Tegretol, Sodium Cromglycate eye drops with Vividrin and NostrilVet but to no avail. He has had an x-rays of head and neck as well as an endoscopy of his nasal passages but nothing untoward was found. His head shaking is worst whilst being ridden but he will sneeze and shake when being led to/from paddock and occasionally sneezes in the paddock as well.

Any suggestions as what else I can try to alleviate his problem would be greatly appreciated.


WTD said...

Hi, i am in Sydney Australia. I have two horses one TB 24yrs old, and an Australian Stock Horse 16 years old, My TB has been headshaking for 4 years now and my stockhorse has just started this season, both horses scoped recently and found mucus nodules right up the back of their nose. My SH is on cyproheptadine tablets 300mg per day, and previously on Predys, very high dose for 10 days, and boxed all day. To me this is an allergic reaction to something seasonal, and the headshaking is the visual sign of something of the pain that the infection is causing. Fly veils make no difference, the only thing that helps when they are distressed is with wetting their nostrils, rubbing up in side their nose, or rubbing their head above their eyes, any suggestions would be helpful, its going to be near impossible to locate an offending plant or weed, my property is practically weed free, all paddocks have been pasture improved, the only thing that is questionable is i have photenia (red tip) surrounding my arena


Anonymous said...

Hello Doc,

What about a horse that has a left ear twitch, a little snorting at the start of the ride pretty much goes beautifully and then WAM a big violent toss to the right? Like almost falls over? Does it at any gate (canter, hand gallop...) would throw her head into a fence if it were there. And then is quiet again, goes really nice. Still fusses with her left ear. Hates sun and wind.

Kel said...

Hi everyone

I found out today my 20yr old horse has head shaking syndrome. He shakes his head a little to the side but the strange thing is he will suddenly act as if he got stung in his knose and just bolts (if you are on him or next to him) This is so unlike him...:( when he stands next to me he rubs his knose on his leg or me - clearly somethings bugging him I just wish I can help him.

Hoffy said...

hi I have an Andalusian who's head shaking has become very out of control in the last year. The vet has suggested head shaking, as he is very sensitive and often freaks out when the doors are open or light comes into the arena. Theres No way it is strictly behavioral. Recently a long fly mask has helped calm him during my rides, however, he has begun to kick his stall throughout the day when I am not there.. so hard that we fear he may kick through to the next stall.

I believe this is due to pain.. any idea of how to control this or help him calm down? Anyone had similar problems?

Dr. Alan Weldon said...

This sounds a great deal like photic headshaking. Ask your Vet about the use of cyproheptidine. It is a difficult diagnosis to arrive at so a lot of causes will have to be ruled out.

JWW said...

2 posts follow, one on ears, and one on headshaking.

1. Ears. I had a TB mare with "Aural Plaque" (spelling) After years of thinking she was better, then her getting worse, I just got into the habit of taking her bridle apart and putting it on around her ears. Once she realized I was going to bypass them always she got much better. No vet treatment ever worked.

2. Headshaking. I brought a TB gelding to AZ from VA. The vet in AZ floated his teeth with an electric float. He developed Headshake...I can't say that't what caused it, but $3000 worth of xrays showed irritation around his teeth and around a cut he had had sewn up 6 weeks earlier. (3 weeks earlier in Virginia he won his division eventing. Won the trophy in dressage...etc. So now a year later it's gone. But he was unridable for 5 or six months. I had an old fashioned (ie by hand) equine dentist touch him up, and and acupuncturist work on him and that made it better. I did try keeping him in with a mister/fan, that did not help. The vet ruled out sun, he had no issues there. But it could have been an allergy, I just don't know, and I've moved him since, so it hasn't recurred.

Susan House said...

I have a 15 yr old paso fino gelding who was, up until the middle of May, a very pleasant and easy-going horse. He first presented with a sudden almost violent vertical head shaking. Vet was called immediately and diagnosed and treated for colic. He was fine for two days. The head jerking started again, not as violent, but a rythmic jerk. Can't put a halter on him - goes beserk. He paces in his stall and blows and paws at same spot in the corner. Has separated himself from the other horses when in pasture. My vet has treated him for colic 2x, ear mites, floated teeth, did an endocsopic exam. And now wants to treat for EPM. He had one positive and one negative EPM test. He has no symptoms in his legs or hind end. I asked my vet about head shaking syndrome and he said he wants to rule everything out before we "go down that road" My horse is miserable. Please help. I am having a new vet come see him on Tuesday and I wanted to get your insight for a discussion with her.
Thank you!

Dr. Alan Weldon said...

It sounds more like a head shaking problem than colic although that is much more common. Other neurologic disorders are also possible and EPM can be considered but it's an atypical presentation. Serum or blood testing is extremely unreliable, the best test is to test spinal fluid using the SAG 234 ELISA test at the Univ of Kentucky. It does sound a lot like a head shaking case from this end. The going off by himself is particularly interesting.particularly if he is seeking out shade.this could indicate an ocular cause or photic head shaking . As a quick test...try a fly mask and keep him in on bright sunny days, if he is only doing it when in the sun then you are moving towards a diagnosis. If not then other cause need to be considered as it is a syndrome with a lot of factors involved....keep me posted.

Unknown said...

Hi, i have 2 headshakers on the one property, both starting 4 years exactly to the month of being here. Both have inflamed nasal cavities, with dripping mucus, clear to white nasal discharge and some tearing - only from one eye though.
They have had a massive diet change - no green, pasture is removed when actively growing and it did improve the situation and reduce the severity by around 80% last season.

Do you have any theories on k:na being out and k binding calcium and magnesium, sodium and chloride - chloride depletion leads to metabolic alkalosis. Also underactive adrenals leads to potassium being retained, sodium/chloride being excreted and should be the other way around.


Dr. Alan Weldon said...

Dear "unknown"
There is no published data concerning electrolyte abnormalities and head shaking syndrome. Adrenal dysfunction " addisons disease" is rare in the horse but a condition similar to relative adrenal insufficiency is reported in those suffering from septicemia. Sounds unlikely in this case. The fact that there were moved to a new location and signs started points to a more environmental cause. This could be allergic in nature , reactions to molds,pollen or certain cleaning fluids if used. Also a sinusitis is a possible cause but doubtful it would go on in two horses for four years. Diagnostic plan should include endoscopy, skull radiographs,...if clear then a trail course of corticosteroid may be indicated.

Unknown said...

Hi, thanks for this. They have been scoped which is why we found the inflamation. Both these horses were not on hand fed minerals just the blocks and salt licks which they never used, just sat gathering dust. My pastures also are out, high k and mg, low ca and p, and zero na. Both horses are supplemented, broad spectrum supps + ca/mg supp and salt - 40g per day. From all accounts these two horses have deleloped allergies as a part of HS. The adrenals are exhausted, and cause is due to soil imbalance, no force fed supplementation and superphosphate being spread over the soils previously which meant they were eating potassium rich pastures 24/7. They have been on cypro and predys granuals initially cypro had no effect, garlic and rosehip however had impact around 40 days. A diet change and removal of all processed feeds and alfalfa has seen 1 of the horses ratios come into acceptable range, the other with the insufficient adrenals and overactive thyroid is still out. Hes now on a herbal mix to help get his adrenals working properly so that he can excrete the excess potassium and retain the sodium. If you were treating a horse with adrenal and thyroid problems - forgetting the fact of the allergies how would you treat that.


Ashley&Buddy said...

Hi, I have a now 8 year old palomino paint gelding. He started Head-Shaking at age 5. It started out very mild and got to where I was no longer able to ride him. He went from a near bomb-proof horse to one that was fearful of almost anything that moved. I took him to the University of Florida Large Animal Clinic, they had no clue gave us no answers. He twitches most when asked to move (walk, trot, canter) at rest though it can be just as bad as when moving especially if you've just gotten off from riding. ONe thing I've noticed is he sucks his chin (squishy part under his lower lip) flat I mean completely FLAT when working. I have never seen a horse do this. He's rubbed his nose bloody before but hasn't done that in quite a while. Please I'm begging you, I need answers anything that might help him :( No one will give me answers, I just want to help Buddy in any way I can he's my best friend :(

Anonymous said...

I have a 9 yr thbd that I have had for 6 years.She exhibited headshaking last Feb was treated with dex for a few days which didnt seem to help.The symptoms went away totally within a few weeks.They returned at exactly the same time this year while being vetted.They think she is a headshaker but offered no real treatment/solutions.She is the same whether dark/sunny etc.Does not use her run in shed or other horses tails.Lives out 24-7.It does not affect her being ridden/jumped etc but does do it occasionally while riding.Can you suggest a vet in Va that has experience with this or suggest treatment?Thankyou

Anonymous said...

I have a 10 year old thouroughbred that has a terrible habbit of head tossing. I have tried so many things to fix it because its just a nightmare! He hasnt always done it, he has only recently started doing it again. He stopped for a while and we thought we had solved the problem because we had the saddles re fitted as he was pulling up sore in his back. He wasnt great strate away but about a couple of months ago i had him going around like a school horse. Just lately he has been absolutly shocking with his head and its causing me so much stress and worry. At my last event, the dressage was horrible. We took him to morphett ville vets to get him checked out because one of our friends had a horse with the same symtoms. There horse ended up having a problem with one of its hocks which was making him nappy and uncooperative in work. He also had a sore back as he was compensating for his hock. They got him cortizone injections put into his hocks every 12 months and he was fine and went on doing grade 1 eventing. So we thought we might have the same issue. So we took him and the vets said he is showing sighns of disconfort in his hocks. They took exrays and he showed slight signs of atheritus. So we had the cortizones put in.
I have ridden him twice since, yesterday and the day before and he is still doing the head tossing as if there are flys annoying him or somthing, but there was no flyes? its unexplainable and im so frustrated by it! I dont know what else to do. HELP PLEASE!

Thankyou, Emily.

Jeanne said...

I bred and raised my Morgan Mare who is now 8 yrs old.
Classy is my 3rd generation foal and I have never had or seen a head shaker before. Last year there was an
out break of Rhino and we vaccinated all the horses in the barn. I have a boarding and training stable so we
are very careful not to spread or share potential illness.
A couple weeks after her vaccination she started kicking her stall walls and being basically a brat under saddle.
Had the vet look at her teeth and a chiro adjust her. We also have a chiro who works on our
horses and with her second visit we (trainer, chiro & myself) were standing there watching her and talking about
what her attitude maybe from and she started bouncing her nose. I had never seen it before but the our Chiro had. Classy has always been on a grass hay or grass mix, orchard or timothy grown in the same valley the
last couple of years. I tried the magnesium, melatonin, lysine, and also had her on a clay for possible ulcers.
None of these has really worked, also she was moved to a dark stall and wears a face mask. The kicking
has stopped but not the "tick". Also she usually does well under saddle although we don't ride her much anymore. Classy is not out on pasture either so it's not a grass issue. I cut out all other supplements and she is not on grain. I know that you said it was not related to the rhino vaccine but that is when everything started. I need to find another vet as this one has said he will call something in to the pharmacy twice now and hasnt followed though...

Jeanette Hennemann said...

I have been thinking possibly could it be an electrical imbalance. All that being said, the meds did help. And the light does bother mine at least. Oddly mine is chestnut also with a large blaze. Thank you for your information.

Anonymous said...

I am a small animal veterinarian and my personal horse has recently developed head shaking syndrome. I would appreciate any information you can give me.

Cindy said...

I have a 7 yr old I also bought in the winter and now that it is spring and summer he has the headshaking ...I purchased this to show AQHA current from a AQHQ judge and so called AQHA horseman of the year...Yea, don't really want to go there...My Vet wants to but my horse on cyproheptidine..but I can't show with Is there anything out there that you can show on?? Are do I have a yard ornament? a 17.5 hands appendix out of Coats and tails ornament...I need help

Anonymous said...

Another headshaker here. 12 yr old ex race horse. He flicks his head upwards and the front legs stomp. This only happens when being worked or on the lunge. I've not noticed him doing this in the paddock. I ride with a nose net and this seems to fix the problem but I cannot compete with it on so competitions become a waste of time. Any suggestions what might be causing it? A vet came and did an examination a few yrs ago and ruled out light sensitivity and said allergies but we've tried all allergy and cortisone treatment available with no success. Chiropractor treatment seems to help for a few rides only. He does this all year round, rain hail or shine.

Also I've heard there is an injection that is proving success with headshaker. It's 3 injections over 3 months. I don't know it's name and don't know a lot about it as yet but if this sounds familiar to u, are you able to provide further information and its success??

Katherine said...

Hello, I know that this may be an old post but I am hoping you still keep up with it. I have an 18 year old Oldenburg chestnut mare that I have owned for three years now. 9 months out of the year she is down in Kentucky while I am at school and is out on pasture for most of the day and comes in at night to around 6 flakes of hay to munch. During the summer, I take her home to Chicago where she is only on hay and grain and in a stall for most of the day due to no pastures on the property. Last year, I was at a different barn and she was out at night and in during the day and have never experienced this. This year, she is out during the day and in at night. When she is out, she has the option of hay or grass and she will switch off. Outside she is fine. But once she is in a stall and munching on hay ONLY (grain and treats do not affect her) she begins to shake her head vertically and try to itch her nose on her leg as if the hay is tickling her with every bite. Once the hay is in her mouth, she stops. It is only when she has strands hanging out. However, if she eats small enough pieces, it does not seem to bug her and when I hand feed her hay that I have folded into a tight ball she is okay. It worries me because she just started doing this back in January for the first time after I started treating her for a back problem. At first I thought it was the medicine I had her on and she developed an allergic reaction because once she was off of it, the shaking had stopped. But a few days ago, she randomly started up again, this time not on medicine. She gets a powder in the mornings I ride her but she was not on that the day she started and the week before, she was not expressing any signs of irritation during dinner while taking the powder in the mornings. She gets ridden about 4-5 days a week, light to moderate depending on her temperament that day, and is never moody. She loves her ears scratched and she likes the sides of her mouth curried. We are currently learning dressage after being a jumper for many years. Riding wise, there is no head shaking, no itching, no discomfort. Only when eating hay during dinner. I do not know if it's just the batch of hay that is in right now, or if she is allergic to something. It hurts me to see her try to eat her dinner during these episodes. She's very willing to eat it, but after a few bites she gets very weary of the hay. I was hoping someone could help. The vet is coming out, hopefully tomorrow, to check up on her.