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What is Grass Allergy?

A grass allergy can be a burden for both you and your horse.  It is rare for a horse to be allergic to any type of food he consumes, including grasses.  It is also rare that he would have a contact allergy type reaction to grass.  However, in the veterinary world, we never say ‘never’; that it is impossible.  More commonly, a horse is found allergic to grass from inhaling the pollen it produces.  It can cause symptoms of respiratory issues or exacerbate any your horse is already experiencing.  

Depending on which type of allergy your horse has to grass, his symptoms can vary as well as his treatment plan.  If it is a contact allergy or ingestion allergy, prognosis of recovery is good.  If it is an inhalation allergy, the severity of his symptoms will directly impact his prognosis.

Horses can be allergic to grass via consumption, coming into contact with it, or inhalation of the pollen.  If your horse is experiencing any type of respiratory distress from an inhalation allergy, it needs to be treated as a medical emergency.  Contact your veterinarian immediately.

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Symptoms of Grass Allergy in Horses

Symptoms of a grass allergy in your horse may include:

  • Generalized pruritus
  • Multifocal pruritus
  • Pruritic urticaria
  • Non-pruritic urticaria
  • Tail rubbing
  • Scratching against posts or other objects 
  • Hives 
  • Alopecia 
  • Respiratory issues

Symptoms typically affect the:

  • Neck
  • Face
  • Trunk
  • Rump 

If the grass is causing a contact allergy type reaction, symptoms may include:

  • Pruritus 
  • Papules
  • Lesions
  • Crusted pustules
  • Scaling
  • Alopecia
  • Hyperpigmentation 
  • Excoriation
  • Lichenification 
  • Secondary skin infection 


Depending on where you live, the species of grass can vary tremendously.  The grasses in the area can also vary depending on the type of soil you have on your property and what season it is at the time of ingestion, inhalation or contact. Ingestion and contact allergies to grass are both rare, but inhalation of the pollen causes the most severe reactions.

Causes of Grass Allergy in Horses

The grass pollens have been known to cause the issues or to exacerbate already developed respiratory related illnesses.  Just like with any type of allergy in general, it is your horse’s immune system thinking something harmless is actually dangerous.  This leads his body to react in the only way it knows how to.  It is thought food hypersensitivity can be a result of a break in the intestinal barrier function and typically develops at a younger age.  A contact allergy can develop over time and may only affect your horse during certain seasons. An inhalation sensitivity can happen at any age and can affect your horse’s respiratory system.

Diagnosis of Grass Allergy in Horses

Your veterinarian will make note of your horse’s symptoms and where they are primarily affecting him on his body if his symptoms are external.  She will also want to collect a verbal history from you for information of when his symptoms began and how quickly they have been progressing.  She will want to know all details as to what your horse has ingested and has had contact with recently in order to help with her diagnosis.  

If your horse’s skin is having the reaction, your veterinarian may want to take a skin scraping sample from your horse or a sample for a skin cytology.  These tests can rule out skin issues that may be affecting your horse.  For example, she will need to rule out skin ailments like parasitic infections or fungal skin infections.  Secondary skin infection can result from raw and broken skin.  

There is no serum, blood, or intradermal test reliable for diagnosing food allergies but it can be used to test for environmental allergies.  It can explain what your horse is sensitive to and by how much.

If your horse is experiencing respiratory issues, your veterinarian may want to take radiographs of the chest to check your horse’s heart and lungs.  She will need to rule out heart disease, pneumonia, and other ailments that can affect his system.  She may also want to proceed with blood work consisting of a chemistry panel and complete blood count.  The results can indicate if there is anything else going on within your horse’s system and will evaluate his organ function.

Treatment of Grass Allergy in Horses

If he is experiencing a contact type reaction, the skin will need to be treated depending on the lesions and symptoms your horse has developed.  If there is a secondary infection, your horse will need antibiotics.  Your veterinarian may also recommend a topical medication which may come in the form of a liquid, ointment, or spray for you to apply directly to the lesions themselves.  

If you horse is allergic to the grass via consumption, you will need to eliminate it from his diet if at all possible.  This can prove to be difficult if the source is the pasture he is on.  This may require you to do some pasture management and maybe even plant other grasses that do well in your specific environment.

If you horse is experiencing respiratory issues, the veterinarian may need to supplement him with oxygen.  She may also administer injectable medications such as an antihistamine and/or steroid to help his immune system calm down and stop the reaction.  If coughing or any other issues are involved, treatment will be administered by the veterinarian as she sees fit.

Recovery of Grass Allergy in Horses

If you are unable to determine the source of the allergy, and therefore remove it from his daily life, you may have to provide your horse lifelong supportive therapies.  This may include oral medications, topical ointments or sprays to control his symptoms.  The severity of his allergy and how exactly it affects him will all play a role in his prognosis of recovery.  Food allergies are rare and the source can be removed from his diet. A contact allergy is easily treatable and you can remove the horse from the source.  If he is experiencing an inhalation allergy, it gets a little harder.  Depending on what, if any, respiratory issue develops, his prognosis of recovery can vary.

Grass Allergy Questions and Advice from Veterinary Professionals

Quarter horse x saddlebred
15 Years
Mild condition
0 found helpful
Mild condition

Has Symptoms


Hello! I believe my horse has a grass allergy. My vet and I have given her antihistamine shots and tablets and she still scratches most of her mane and the top of her tail off as well as causing other lesions on her face and body. She’s scratched so much she’s broken the door on a stall or two. When we go out of town camping for a week she is completely off grass during the time and her symptoms clear up. But as soon as she is home and back in the pasture, it starts all over again. It happened at our old home as well as the new one. We’ve determined it’s most likely a grass allergy. What are some ways that I could help ease her discomfort? I’m currently giving her Benadryl and a topical antihistamine spray. Is there anything I could bathe her in routinely to help as well? I just want her to be comfortable during the spring and summer months when it’s at it’s worse, which also seem to be the only time it flares up.

Dr. Michele King, DVM
Dr. Michele King, DVM
1611 Recommendations
There are probably topical shampoos that you can use, and there may be other medications that can help Karma. Without seeing her, I'm not sure what therapy she may need, but you can definitely call your veterinarian, let them know what is going on, and see what other medications may be available for her.

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RR Indian Firestorm (Smudge)
16 Years
Moderate condition
1 found helpful
Moderate condition

Has Symptoms


We have been trekking in a different area to where we live and my horse has come home with hives all over his body, these were as-berated when he overheats.
I am 100% sure they are not licks, lice or biting flies, this is not the first time while we have been trekking he has broken out with them.
I give him a toxin binder, magnesium and salt everyday in his feed.
It seems like this is the only time of the year he breaks out with them and taking notice of grasses the only difference would have to be Kakuyu and 70% more paspalum in the pasture.
Is there anything I can give him to alleviate the discomfort for him?

Dr. Callum Turner, DVM
Dr. Callum Turner, DVM
3320 Recommendations
Ideally if Smudge is breaking out in hives while trekking in a new area, it would be best to revert back to your old trekking area and to give him a good washdown to remove any possible debris on the skin or coat. Products like Benadryl (diphenhydramine) can be used in horses at 0.25-0.5mg/lb but can add up to a lot of tablets each dosage, twice per day; I would recommend you discuss with your Veterinarian over the phone and they may be able to supply you with a prescription product if you have an existing current relationship. Regards Dr Callum Turner DVM

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