Chronic cough without fever in horses

Hay mold is one of the most likely causes of coughing in horses.
Hay mold is one of the most likely causes of coughing in horses.

Chronic cough in horses is a common problem and can be a challenge to diagnose, writes Robert N. Oglesby DVM.

Despite many possible causes there are two which are most likely: mold dust in the hay and an upper respiratory tract infection.


Physical exam: horse and hay

Whenever a horse presents with a cough a thorough exam is warranted. The most common causes may be difficult to prove with an exam but more serious causes can be eliminated. Temperature, examination and palpation of the throat, auscultation of heart and lungs, and a look at the hay should all be done. If the horse has been non-responsive to treatment then an endoscopic exam of the pharynx, larynx and trachea is warranted. This will help rule out inflammatory problems there.

A developing allergy to hay mold and recovery from a viral infection are two common causes of a cough with few other clinical signs. Careful exam and history along with examination of the hay will usually lead you to the correct answer.

Contrast these differences:

  1. While exercising, the cough from hay allergies improves, but the cough from a recovering infection will worsen. The exercise and coughing helps the horse clear out the secretions caused by the allergy, but will irritate the pharyngitis.
  2. The horse with pharyngitis will sometimes demonstrate sensitivity to laryngeal and upper tracheal palpation while the allergic horse may have changes in the lung sounds on auscultation. In mild cases you may find neither.
  3. Does the hay have a musty odor? When you first open the bales do you see a little cloud of “smoke” that disappears rapidly? If the answer to either question is yes: be suspicious of mold allergies.


Treatment for Pharyngitis

Horse’s with mild pharyngitis will respond to stall rest. Usually 21 days is plenty of time and if the cough persists beyond that, further work up is warranted. If you strongly suspected pharyngitis, and the hay was excellent, examine the pharynx with an endoscope.

If nothing turns up on re-exam try treating him for hay allergies. Or even better, wet the hay while resting him for the pharyngitis. Once he is over the cough begin him back on good hay. If the cough returns when he is put back on hay you have your culprit.


Treatment for allergies to hay mold

If you suspect hay allergies, begin by removing hay from his diet. Either leave him out on pasture, feed cubed hay, or use one of the hay substitute feeds made for heavy horses. If these are not practical you can try thoroughly soaking the hay just before feeding. If the horse shows improvement over the following week you will need to be more careful about the quality of your horse’s hay. Continued exposure to hay that makes him cough will only make him more sensitive and can lead to heaves.

Corticosteroids can be used to help a horse get over the effects of exposure but must not be used as a substitute for removing the cause.

Hay allergies can progress to a permanent debilitating disease.

In the early stages of hay allergies a light cough develops that disappears as the horse works. As the disease progresses the horse’s cough begins to worsen and then breathing becomes difficult. What is happening is that long-time exposure to the hay molds is causing permanent changes in the lungs, reducing the amount of air he can breath in. When a horse becomes affected to the point of difficult breathing he is said to have heaves.


This article reprinted with permission from, an internet information resource for the equestrian and horse industry since 1994. On the WWW at we have tens of thousands of documents on the web about horse care, diseases, and training. © 2005



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4 thoughts on “Chronic cough without fever in horses

  • September 10, 2016 at 2:10 pm

    can allergies to hay make the horse loose weight?

    • September 19, 2016 at 2:29 am

      My horses are both coughing horrible though it was the saw dust

  • March 19, 2017 at 5:59 pm

    My horse coughs whenever she is exercised and it does not improve throughout the workout. She also has a strange gurgling sound inside of her right before she starts coughing.

  • October 5, 2017 at 5:14 pm

    hi my horse is old(23) and is coughing every few minuets, she is slitely losing her appeeite for her hay. the cough is dry and she struggles as she coughs. it has been very cold latley,and she has been in a stable wearing a cover the whole time. her nose is slitely runny. please tell me what you think,Sophia.


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