Page 936 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Endocrine system 911

VetBooks.ir head, muscle fasciculations, laryngospasm, brux- comprised of 2 parts NaCl, 1 part KCl and 1 part
limestone, every 2 hours, to horses participating in
ism and profuse sweating. Serum calcium <1.25
mmol/l (5 mg/dl) causes recumbency and stupor.
Hypocalcaemia causes cessation of GI motility, heavy endurance exercise will prevent electrolyte
imbalances caused by sweating.
which can then lead to intestinal distension, colic Several products are available for i/v administra-
and gastric reflux. tion of calcium, including calcium gluconate (avail-
able alone or in combination with dextrose and
Differential diagnosis other electrolytes), calcium borogluconate and cal-
Differentials depend on the severity of clinical signs cium chloride. There is no published ‘safe’ rate for
but can include GI upset (colic), tetanus, hyperka- calcium administration, as there is for potassium
laemic periodic paralysis (HYPP), myositis, equine administration. While it is possible to administer
motor neuron disease or other neurological disease 23% calcium gluconate slowly and directly from
(e.g. West Nile virus [WNV]) encephalitis, rabies, the bottle, it is safer and less irritating to the vein
equine protozoal myeloencephalopathy [EPM]). to dilute it in fluids. In severe cases of hypocalcae-
mia, it should be safe to give approximately 500 ml
Diagnosis of 23% calcium gluconate (diluted in fluids) over
Definitive diagnosis is made by measurement of a 1-hour period. The heart rate should be moni-
serum ionised calcium concentration. If only total tored, and the calcium infusion slowed or stopped
serum calcium concentration is available, it should if bradycardia or an arrhythmia develops. In gen-
be corrected for serum albumin levels (see below): eral, when an exact serum calcium concentration is
unknown, it is safe initially to add 100–150 ml of
Correct total serum calcium (mg/dl) = measured serum 23% calcium gluconate per litre of fluids and give
calcium (mg/dl) – serum albumin (g/dl) + 3.5 the resulting solution as fast as 2–3 l/hour to the
average 500 kg horse. This would be the equiva-
In the absence of immediate laboratory results, lent of adding 500–750 ml calcium gluconate to a
diagnosis should be suspected based on clinical signs, 5 litre bag of fluids and giving that over a period of
a history of predisposing conditions and response to at least 2 hours. For prolonged calcium supplemen-
therapy. tation (e.g. 24 hours), in the absence of the facility
to monitor serum calcium concentrations, it is usu-
Management ally safe to add 100–150 ml calcium gluconate per
Calcium is well absorbed by the GI tract of horses. 5 litre bag of fluids, administered at 1–2 times the
Normal adult horses should consume approximately maintenance fluid rate.
40 mg/kg calcium per day; pregnant or lactating Proper dietary management may help prevent
mares or horses participating in endurance exer- hypocalcaemia caused by exertion, sweat loss
cise may need more than this. Mild cases of hypo- or lactation. While it is important to feed high-
calcaemia can be treated by oral supplementation risk horses such as pregnant mares or endurance
with calcium in the form of limestone or simply by horses a diet that meets calcium requirements, it
feeding alfalfa hay. Limestone (calcium carbonate) is probably not necessary (and may be contraindi-
is 40% calcium and contains no phosphorous. For cated) to feed these horses diets high in calcium
treatment of mild episodes of hypocalcaemia, such as before parturition or during training. It is thought
might occur in a horse just completing an endurance that routinely feeding excessive calcium promotes
event, 20–60 g limestone can be administered orally pathways for calcium loss through the GI tract

over several hours. The limestone can be sprinkled and kidneys. The body is then not hormonally
on a small amount of grain or administered as a paste prepared to deal with an acute demand for, or loss
directly into the horse’s mouth. It has been suggested of, calcium. Feeding an adequate, but not exces-
that administration of 30 g of an electrolyte mixture sive, amount of calcium in the diet keeps the PTH