The ABC of al­ler­gies

Dr Michelle Logan looks into the sea­sonal prob­lem of al­ler­gies in our equine friends IM­AGES BY DUSTY PERIN

NZ Horse & Pony - - In This Issue -

The preva­lence of al­ler­gic symp­toms in horses is on the rise; we look at some of the rea­sons be­hind this, and how to take care of the suf­fer­ers

Al­ler­gies are a chal­lenge; they re­sult in a wide range of prob­lems and seem to be be­com­ing ex­tremely com­mon. Do you know of a horse who coughs when sta­bled and has to have hay damp­ened down? Or one who comes out in strange lumps out in the pad­dock? Or even one who is con­stantly rub­bing him­self in the spring? Then you very likely know of a horse with an al­lergy prob­lem.

What ac­tu­ally is an al­lergy?

Just like in peo­ple with hay fever or those who re­act strongly to in­sect bites, an al­ler­gic horse is one where the af­fected part of the body is mak­ing an in­flam­ma­tory re­sponse to fight off some­thing from out­side the body which is classed as an ‘in­vader’ (or what we call an anti­gen).

The in­vader in this case could be pollen, in­sect saliva, a fun­gal spore, dust mite and so on. In the case of an al­ler­gic re­ac­tion, this in­flam­ma­tory re­sponse has gone into over­drive; it is way over the top to what is needed to pro­tect the body. We call this be­ing ‘hy­per­sen­si­tive’.

To show a true al­ler­gic re­ac­tion, the horse has to have been ex­posed to the in­vader be­fore, and then cer­tain cells are pro­grammed to re­spond in this ex­ag­ger­ated way when they get re­ex­posed. The re­ac­tion will be­come stronger as the horse is ex­posed to the in­vader again. So, although it may seem as if your horse has sud­denly de­vel­oped an al­lergy, in fact it was al­ready pre­dis­posed and just hadn’t been ex­posed to the trig­ger enough times to set off a big enough in­flam­ma­tory re­sponse to show the al­ler­gic signs.

What are the dif­fer­ent al­ler­gic re­ac­tions we see in horses?

ANA­PHY­LAC­TIC RE­AC­TION This is the most dra­matic and for­tu­nately very rare. It is the strong­est al­ler­gic re­sponse and the horse can go into ana­phy­lac­tic shock and can die. In peo­ple we see it more com­monly with al­ler­gies to peanuts or bee stings. In horses we some­times see it as a rare drug re­ac­tion; the air­ways swell and the heart can stop un­less treat­ment can rapidly be given.

Much more com­monly we see milder ei­ther res­pi­ra­tory or skin signs. RES­PI­RA­TORY AL­LERGY SIGNS Al­ler­gic res­pi­ra­tory signs can look the same as other res­pi­ra­tory prob­lems with cough­ing, runny nose and poor per­for­mance. The al­ler­gic re­ac­tion is to par­ti­cles in the air that is breathed in; the par­ti­cles caus­ing the al­lergy can be fun­gal spores and dust par­ti­cles, amongst oth­ers.

The al­ler­gic re­ac­tion re­sults in the air­ways be­com­ing nar­rower (due to the air­ways con­strict­ing plus ex­tra mu­cous and in­flam­ma­tory cells be­ing pro­duced in the lungs). The air­ways also be­come very re­ac­tive (hy­per­sen­si­tive) so any fur­ther trig­gers will cause more mu­cous, more in­flam­ma­tory cells and the air­ways will con­strict fur­ther, so less and less oxy­gen can be taken in. This is why we see cough­ing, nasal dis­charge and why the horse isn’t able to per­form as he should – he can’t get as much oxy­gen into the blood­stream to reach the mus­cles of the legs and heart.

Re­cur­rent air­way ob­struc­tion (RAO), chronic ob­struc­tive pul­monary dis­ease (COPD), heaves and equine asthma are all names for the al­ler­gic air­way dis­ease we see in horses. The con­di­tion usu­ally starts in ma­ture horses and is very com­mon in coun­tries where horses are sta­bled for a lot of the time (and so are more of­ten ex­posed to dust and fun­gal spores found in hay), although there is a pas­ture-as­so­ci­ated con­di­tion which likely in­volves an al­lergy to pol­lens. SKIN AL­LERGY SIGNS Another place we com­monly see signs of al­lergy is the skin. This can be due to ex­ter­nal fac­tors eg. pollen, in­sect bites and sham­poos, or can be an al­ler­gic re­ac­tion to some­thing eaten. One well known skin al­lergy is sweet itch; this is re­ally a hy­per­sen­si­tiv­ity to a par­tic­u­lar type of midge (Cul­li­coides) which at present we don’t have in New Zealand, for­tu­nately. We do, how­ever, see very sim­i­lar in­sect

hy­per­sen­si­tiv­ity signs caused by other types of fly­ing in­sects.

The re­ac­tion can cause in­tense itch­i­ness; I have seen horses so des­per­ate to rub them­selves on fences that they have ended up in­jur­ing them­selves. You usu­ally see small lumps over the skin con­tain­ing a lit­tle scab. The horse rub­bing it­self can then cause other signs.

Hives are another type of al­ler­gic re­sponse; these are the strange swellings that come up rapidly on the body, like a very large net­tle rash. Find­ing the cause for this can be dif­fi­cult – it may even be re­lated to some­thing eaten – but they usu­ally go away fairly quickly too.

How do we di­ag­nose an al­lergy?

With a sus­pected res­pi­ra­tory al­lergy, your vet­eri­nar­ian will take into ac­count the his­tory and the clin­i­cal signs then per­form a phys­i­cal exam. A lung wash, or bron­choalve­o­lar lavage, may be needed for a de­fin­i­tive di­ag­no­sis.

With skin al­lergy, again the his­tory, clin­i­cal signs and clin­i­cal ex­am­i­na­tion are used for di­ag­no­sis and of­ten a treat­ment or man­age­ment trial is put in place. There are a cou­ple of more spe­cialised tests avail­able; the in­tra­der­mal skin test and the serum IGE test. These have not been used as much in horses as other species yet, so may still need fur­ther val­i­da­tion.

What can you do if your horse is prone to al­ler­gies?

RES­PI­RA­TORY SIGNS If your horse has been di­ag­nosed with re­cur­rent air­way ob­struc­tion, in­flam­ma­tory air­way dis­ease, asthma, heaves, chronic

ob­struc­tive pul­monary dis­ease or even a res­pi­ra­tory virus, you can help by re­duc­ing any fur­ther trig­gers to the hy­per­sen­si­tive air­ways, as well as try­ing to re­move the orig­i­nal source of the al­ler­gic re­ac­tion. Med­i­ca­tion may be pre­scribed by your vet­eri­nar­ian; this can in­clude steroids (in­haled or oral) and bron­chodila­tors amongst oth­ers, so this should be used as well as in­clud­ing the fol­low­ing man­age­ment changes: Dampen hay and cha be­fore feed­ing – this is vi­tally im­por­tant as hay con­tains a lot of par­ti­cles that, if in­haled, can set o the re­ac­tion in an al­ler­gic horse Ide­ally turn out into a pad­dock* or use dust-free bed­ding and have ex­cel­lent ven­ti­la­tion Make sure the ad­join­ing sta­bles have dust-free bed­ding too Don’t store hay near to your horse’s sta­ble or yard Don’t sweep the yard while the horse is in­side En­sure there no lin­ger­ing am­mo­nia (from urine in deep bed­ding) Rest your horse while lungs are hy­per­sen­si­tive – deep breaths of cold air will ir­ri­tate the air­ways, pro­long­ing re­cov­ery Feed­ing from the ground may help the ex­cess mu­cous drain out of the nos­trils *Horses who get res­pi­ra­tory al­lergy when out in the pas­ture (thought to be from pollen) may need to be sta­bled, or put in a di er­ent pad­dock away from sources of pollen. SKIN AL­LERGY SIGNS If med­i­ca­tion is needed for treat­ment, your vet­eri­nar­ian will need to pre­scribe this. Steroids and an­ti­his­tamines may be used. If your horse has the small lumps with scabs these can be­come sec­on­dar­ily in­fected with bac­te­ria and this in it­self can be itchy so a med­i­cated sham­poo can be very help­ful; use an io­dine or chlorhex­i­dine wash.

For pre­ven­tion, if pollen is sus­pected as the cause, then the use of cov­ers and try­ing di er­ent pad­docks at cer­tain times of the year or even stabling may be help­ful. For in­sect hy­per­sen­si­tiv­ity, which is prob­a­bly more com­mon, then use of good in­sect re­pel­lents is im­por­tant. Ones con­tain­ing per­methrin are o en e ec­tive. ey come in di er­ent forms and you may even use per­methrin-im­preg­nated ear tags at­tached to cov­ers. e im­por­tant thing is to keep up reg­u­lar in­sect con­trol.

Look­ing at the en­vi­ron­ment may help; for ex­am­ple, mov­ing the horse away from near a stream where midges are in large num­bers at cer­tain times of the year.

For a food al­lergy that shows up as a skin con­di­tion – which for­tu­nately, is quite rare in horses – it can be very di cult to work out what is the cause. Usu­ally, we start with a very con­trolled diet and once the ir­ri­ta­tion is un­der con­trol we may add in the food con­tain­ing the sus­pect in­gre­di­ent and see

C if the signs are up again.


Al­ler­gic is­sues can be a real chal­lenge to man­age. If you have a horse with al­ler­gies,

MY try to get a plan in place with your

CY vet­eri­nar­ian but be pre­pared for some trial and er­ror along the way. ere are

K o en lots of fac­tors in­volved, so treat­ment and man­age­ment have to be quite in­di­vid­ual although the gen­eral prin­ci­ples will re­main the same. A horse that is prone to be­ing al­ler­gic to one thing will o en be hy­per­sen­si­tive to other things, so re­duc­ing any po­ten­tial ir­ri­tants in the en­vi­ron­ment is only go­ing to help.

ABOVE A nasal dis­charge can be a sign of a res­pi­ra­tory virus ABOVE RIGHT Wet­ting down hay be­fore feed­ing is an im­por­tant part of man­ag­ing an al­ler­gyprone horse OP­PO­SITE PAGE A puffy painful eye caused by a skin al­lergy

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