Page 429 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

404 CHAPTER 1

VetBooks.ir partum) predisposes to hypocalcaemia. In mares, it total calcium levels are unreliable, because the ion-
ised fraction within the total level is affected by pro-
may occur immediately before foaling up to the end
of lactation. Mares producing large amounts of milk
(phosphorus, potassium, chloride, sodium and mag-
and eating diets low in calcium, or performing phys- tein levels and acid–base balance. Other electrolytes
ical work, are at high risk. Horses with severe hypo- nesium) should also be assessed. There may be signs
calcaemia may develop a rhythmic movement on of dehydration and metabolic alkalosis.
the flank from diaphragmatic contractions that are
synchronous with the heart beat (see Diaphragmatic Management
flutter, below). This synchronous diaphragmatic The treatment of choice consists of the intrave-
flutter or ‘thumps’ has been reported in horses with nous administration of calcium gluconate solution
gastrointestinal disease, sepsis, lactation tetany, (500 ml of 20% solution [for a 500 kg horse] diluted
blister (cantharid) beetle toxicosis, endurance exer- in 2 litres of 0.9% NaCl solution and given over
cise, hypoparathyroidism and alkalosis. Exercising 10–20 minutes). This dose may be repeated as
horses often develop alkalosis from hyperventilation required to affect. Parenteral calcium therapy is
(respiratory alkalosis) and this results in increased extremely important in horses that develop hypocal-
binding of calcium and magnesium ions to albu- caemia rapidly or in horses at risk of ileus. Even in
min, leading to ionised calcium hypocalcaemia and mild hypocalcaemia, therapy should be considered as
hypomagnesaemia. delaying may result in complications such as ileus or
arrhythmias, particularly as horses with functional
Clinical presentation kidneys can eliminate large amounts of calcium.
Increased muscular tone leads to generalised stiff- Hypocalcaemia may not resolve in some horses until
ness, hypometria, muscle fasciculations and cramps, they receive magnesium supplementation. Ionised
notably in the facial muscles (trismus, temporal calcium and magnesium levels should be monitored
and masseter twitching), neck and trunk muscles, frequently to assess response to therapy.
and occasionally in large forelimb muscle masses.
Muscular hyperactivity leads to hyperthermia and Prevention
profuse sweating, which can cause severe dehydration. Analysis of the mineral intake in the feed and cor-
Other clinical signs include depression, tachypnoea, rection of Ca/P imbalances are paramount. Excess
dysphagia, hypersalivation and colic. If untreated, the phosphates in the diet will prevent absorption of the
disease may progress to diaphragmatic flutter, cardiac calcium, thus worsening the situation. Predisposed
dysrhythmia and, in severe cases, ataxia, recumbency, horses and lactating mares should be protected from
convulsions and eventually death within 24–48 hours. unnecessary stress or exertion.

Differential diagnosis Prognosis
Severe exertional rhabdomyolysis; tetanus; other The prognosis is usually good with prompt treat-
causes of severe electrolyte imbalances; exhausted ment, but severe forms may not respond to treatment.
horse syndrome.
EXHAUSTED HORSE SYNDROME
Diagnosis
The clinical signs are relatively typical. They are Definition/overview
tetanus-like, but a medical history of vaccination Exhausted horse syndrome is very similar to hypo-
and lack of a wound helps to orient the clinician calcaemia. The condition relates to a syndrome of
towards a diagnosis of hypocalcaemia. On blood muscle hypercontractility induced by severe electro-
analysis, the serum ionised calcium concentration lyte and acid–base imbalance in horses after a period
should be ≥10 mmol/l. Signs become obvious below of hard, sustained exercise. It is most commonly
8 mmol/l and severe below 5 mmol/l. Unfortunately, encountered in endurance horses competing over
ionised calcium analysis is not always available and long distances, and especially in hot weather.