EQUUS - - Contents - By Lau­rie Bon­ner with Melinda Freck­le­ton, DVM

Thumps: This rhyth­mic twitch­ing of the mus­cles near a horse’s flanks are a warn­ing that his in­ter­nal cal­cium re­serves are run­ning low.

Syn­chro­nous di­aphrag­matic flut­ter, called “thumps,” is a meta­bolic disorder with a dis­tinc­tive out­ward sign: The mus­cles along the horse’s flanks twitch rhyth­mi­cally in time with his heart­beat---up to 50 or more times per minute. The af­fected horse is not in pain and will be­have nor­mally.

Thumps de­vel­ops when a horse’s cal­cium re­serves run low as he ex­erts him­self. Cal­cium helps reg­u­late nerve func­tion---specif­i­cally, it acts as a gate­keeper that helps a nerve at rest re­main at rest. But when serum cal­cium lev­els drop, nerves can be­come “ex­citable,” prone to fir­ing in­ap­pro­pri­ately. The phrenic nerve, which con­trols the move­ment of the di­aphragm mus­cles and passes over the base of the heart, is the source of thumps. When cal­cium lev­els are low, the phrenic nerve can fire in re­sponse to sig­nals meant for the nerves that con­trol the heart­beat---which makes the horse’s flanks twitch in syn­chrony with his pulse.

Thumps is most preva­lent in en­durance horses and oth­ers who work long hours, but it can oc­cur in any horse who sweats con­tin­u­ously for ex­tended pe­ri­ods with­out eat­ing and drink­ing. It can also hap­pen after longdis­tance shipping.

Treat­ment is ba­sic---stop work­ing the af­fected horse, and give him time to rest and re­cover with plenty of wa­ter plus his nor­mal diet. If thumps do not sub­side within 15 min­utes or so, call your vet­eri­nar­ian. Un­less your horse has done this be­fore, your vet­eri­nar­ian will want to do some blood­work and may ad­min­is­ter in­tra­venous flu­ids.

Usu­ally, a horse needs at least a few days to re­store his in­ter­nal fluid and min­eral bal­ances. Once your horse has re­cov­ered from a mild case, your vet­eri­nar­ian is also likely to ad­vise you

about man­age­ment strate­gies that can pre­vent another episode. Th­ese rec­om­men­da­tions ap­ply only to horses who have de­vel­oped thumps be­fore.

1. Con­di­tion your horse ap­pro­pri­ately. Reg­u­lar ex­er­cise does more than get a horse’s mus­cles fit---it pre­pares his meta­bolic path­ways for the changes they’ll un­dergo to support stren­u­ous ef­fort. Talk to your vet­eri­nar­ian or a trusted trainer if you need help de­vis­ing a fit­ness reg­i­men for your horse and your in­tended ac­tiv­i­ties.

2. Keep your horse cool. Any horse will sweat while work­ing hard, es­pe­cially in hot weather, but the steps you take to cool him by other means will help to limit his loss of elec­trolytes0. For ex­am­ple, wet him down be­fore rid­ing on hot days, and take breaks to splash wa­ter on him as you go.

3. Elim­i­nate or re­duce his ra­tion of al­falfa hay. Al­falfa con­tains high lev­els of cal­cium, and while it may seem coun­ter­in­tu­itive, a diet that is too high in this nu­tri­ent can lead to de­fi­cien­cies when the horse works. In ef­fect, when the horse’s body is used to hav­ing ex­cess amounts of serum cal­cium avail­able, it loses the abil­ity to call up re­serves dur­ing an ex­ten­sive work­out. Re­plac­ing al­falfa with grass hays, which con­tain less cal­cium, is enough to elim­i­nate thumps episodes in some horses prone to the con­di­tion.

4. Limit bran mashes. Cal­cium and phos­pho­rus are two of the most abun­dant min­er­als in a horse’s body, and he needs to con­sume ad­e­quate quan­ti­ties of both to keep his bones strong and his cells func­tion­ing well. How­ever, it is im­por­tant that the horse con­sumes the min­er­als in a ra­tio of at least 1.2 parts cal­cium for ev­ery 1 part phos­pho­rus---too much phos­pho­rus in the diet in­hibits a horse’s abil­ity to ab­sorb cal­cium. Wheat bran, a common base of hot mashes, is high in phos­pho­rus. A bran mash once a week or so isn’t go­ing to up­set a healthy horse’s nu­tri­tional bal­ance, but don’t make it a daily sta­ple. Rice bran in its nat­u­ral state is also high in phos­pho­rus. If you choose to feed rice bran, se­lect a prod­uct for­mu­lated for horses that in­cludes added cal­cium car­bon­ate. 5. Use elec­trolyte sup­ple­ments ju­di­ciously. A sweat­ing horse loses prodi­gious amounts of elec­trolytes---cal­cium as well as sodium, potas­sium, mag­ne­sium, chlo­ride, bi­car­bon­ate and phos­phate---all of which he can re­plen­ish on his own after a few days with ac­cess to grazing or hay plus a salt block. But any horse who sweats heav­ily for at least an hour or two with­out eat­ing or drink­ing could ben­e­fit from an elec­trolyte sup­ple­ment to help him re­cover faster. Ad­min­is­ter­ing elec­trolytes may help a horse with thumps re­plen­ish his stores, but do not “over­dose” him in an at­tempt to speed his re­cov­ery. Al­ways of­fer plenty of fresh wa­ter to any horse rest­ing after ex­er­tion but es­pe­cially after you’ve given him elec­trolytes. Bet­ter yet, of­fer the horse one bucket of plain wa­ter and one with dis­solved elec­trolytes so he can take what he needs.

This rhyth­mic twitch­ing of the mus­cles near a horse’s flanks is a warn­ing that his in­ter­nal cal­cium re­serves are run­ning low.

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