YH 454 combined pdf

Your horse’s care
-
Endocrine
upsets
When parts of the endocrine system fail
to work properly, it can cause:
Hypothyroidism is rare in adult horses,
despite many conditions such as obesity,
laminitis and insulin resistance being
attributed to low concentrations of thyroid
hormone. However, it may occur in foals
born to mares who are fed inappropriate
amounts of iodine during pregnancy.
Thyroid adenoma You may have noticed
that some older horses have thyroid
glands that are very easy to feel. This is
due to benign enlargement, which is really
common and nothing to worry about.
Pheochromocytoma This is a very rare
type of tumour arising from the adrenal
medulla. Some of these tumours will be
‘functional’, which means they continue to
produce adrenaline. The signs seen in horses
therefore mimic situations where high levels
of adrenaline are produced. Horses may have
a high heart rate, increased breathing rate,
anxiety, profuse sweating, dilated pupils,
colic due to reduced intestinal motility and
high blood sugar. While surgery to remove
the adrenal gland would often be curative,
the complexity of the surgery means that
euthanasia is the more likely outcome.
Primary hyperparathyroidism This occurs
when the chief cells in the parathyroid
secrete excessive amounts of parathyroid
hormone and no longer respond to the
negative feedback of calcium. The
increased secretion is due to growth of a
parathyroid adenoma, or parathyroid
hyperplasia (over-growth of the gland). This
results in increased blood calcium levels
and, as this involves removing calcium from
bones, the bones suffer as a consequence.
Some older horses have
enlarged thyroid glands,
but generally this is
nothing to worry about
The bones of the face may become swollen,
resulting in what’s known as ‘big head’ or
‘rubber jaw’. Calcium removal from the long
bones can lead to lameness, or even the risk
of spontaneous fracture. Other signs include
weight loss, lack of appetite, lethargy and colic.
Diagnosis is via blood tests and the main
treatment, which is curative, is removal of
the enlarged parathyroid. However, as
mentioned, finding the parathyroid, even
when enlarged, is difficult. The best way to
find it is through a nuclear scintigraphy scan
to highlight the area of the neck where the
parathyroid is located. Once this area is
“Ovarian tumours
may lead to stallionlike
behaviour or
persistent oestrus”
Excessive calcium
in the blood can
result in lameness or
spontaneous fractures
narrowed down, the exact location can be
pinpointed using ultrasonography. At this
point, surgical removal may be possible.
Ovarian tumour Granulosa cell tumours
are the most common tumours of the
reproductive tract of the mare. They can
occur in mares of any age and may lead to
behavioural changes, with either stallion-like
behaviour or persistent oestrus/anoestrus.
In other cases, behaviour is normal, but
colic signs may occur. Diagnosis is based on
blood testing for hormone levels, alongside
palpation of the ovary per rectum and
ultrasonography. Once the abnormal ovary is
identified, it can be surgically removed, with
a good prognosis. Surgery is most commonly
performed laparoscopically (keyhole
surgery) under standing sedation.
92 your horse August 2019 www.yourhorse.co.uk