Equine asthma

Vet notes on the con­di­tion

Your Horse (UK) - - Contents -

The con­di­tion

Equine asthma is a con­di­tion that causes some horses to be hy­per­sen­si­tive to mol­e­cules in the air (known as al­ler­gens). This re­sults in symp­toms that range from mild to se­vere. This hy­per­sen­si­tiv­ity (al­lergy) causes lower air­way in­flam­ma­tion and re­sults in in­creased mu­cus pro­duc­tion and con­stric­tion of the air­ways in the lungs. A par­tic­u­lar type of equine asthma in­volves horses that suf­fer dur­ing summer while spend­ing most of their time out­side. The con­di­tion is better known as summer pas­ture as­so­ci­ated ob­struc­tive pul­monary dis­ease (SPAOPD). It’s thought that SPAOPD is as­so­ci­ated with an in­crease in air­borne par­ti­cles and en­vi­ron­men­tal al­ler­gens such as pollen, mould spores and my­co­tox­ins. Some horses can be af­fected through­out the year and also suf­fer with the more clas­si­cal form of equine asthma called RAO (also known as ‘heaves’) when sta­bled and on dry roughage dur­ing the win­ter. SPAOPD is most com­monly seen in horses that are aged seven and over.


In summer, horses with SPAOPD have symp­toms that can be mild to se­vere. These in­clude the oc­ca­sional cough, cough­ing dur­ing ex­er­cise, nasal dis­charge and/or laboured breath­ing. Mod­er­ate to se­verely af­fected horses will have no­tice­able nos­tril flar­ing and ab­dom­i­nal ex­cur­sions dur­ing the res­pi­ra­tory cy­cle (sim­i­lar to those seen with ‘heaves’). In ex­ces­sive cases, you’ll be able to hear wheez­ing noises while stand­ing be­side your horse’s nos­trils. Horses usu­ally re­main bright, alert and have an ap­petite, but se­verely af­fected horses will get more de­pressed and can go off their food. Symp­toms can vary and be in­ter­mit­tent and de­pen­dent on the weather. For ex­am­ple, on cooler, windier days, a horse’s symp­toms may al­most be non-ex­is­tent, while se­vere symp­toms will ap­pear on hot, hu­mid days.


Di­ag­nos­ing SPAOPD in mod­er­ate to se­verely af­fected horses is of­ten based on clin­i­cal signs, such as laboured breath­ing with flar­ing nos­trils, wheezes when lis­ten­ing to the heart and lungs and the ab­sence of a fever. These symp­toms are con­sid­ered in re­la­tion to your horse’s man­age­ment, as well as any pre­vi­ous his­tory and the time of year. Ad­di­tional tests that can be done may in­clude en­doscopy of the lower air­way and then anal­y­sis of the fluid col­lected from the lungs (also called a ‘lung wash’). Ra­dio­graphs and blood tests can also be help­ful to rule out other po­ten­tial causes.

Bron­chodila­tors (a drug that di­lates the bronchi to in­crease air­flow) can open up the lower air­ways, while mu­colytic drugs may loosen mu­cus. Some horses may need a course with glu­co­cor­ti­coids – these drugs stop the hy­per­sen­si­tiv­ity re­ac­tion. Many of these can be given by in­jec­tion, orally or in­haled. In­hala­tion ther­apy may be a better long-term op­tion as the drug dose is tar­geted to the res­pi­ra­tory sys­tem, min­imis­ing side ef­fects. Some horses ben­e­fit from an­tibi­otics if the air­way mu­cus has al­lowed for bac­te­rial growth. It’s im­por­tant to min­imise al­ler­gen ex­po­sure, so horses with SPAOPD will ben­e­fit from stay­ing in­side in a dust-free space when it’s hot and when the pollen count is high.

Your vet will lis­ten to your horse’s lungs to see if he’s wheez­ing

Af­fected horses usu­ally keep their ap­petite, but some can be de­pressed and go off their feed

SPAOPD has been linked to an in­crease in pollen in summer

Summer asthma seems to be weather de­pen­dent and is worse on hot days

Keep­ing horses in a dust-free en­vi­ron­ment on hot days can help

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