granulosa cell tumours (GTCTs) and these can often be diagnosed on the
basis of the clinical signs (e.g. masculinization, nymphomania, prolonged
acyclicty) and the appearance and relative size of the 2 ovaries, i.e. a very
large affected ovary with no palpable ovulation fossa, and an inactive contralateral ovary. However, further hormonal analysis can be helpful when the
diagnosis isn’t clear-cut. Approximately 80% of GTCTs secrete inhibin and,
therefore, raised blood levels of this hormone confirm the diagnosis;
unfortunately inhibin may not be raised in those mares presenting the greatest
diagnostic challenge (i.e. one enlarged ovary but a normally active contralateral ovary). Recently, anti-mullerian hormone (AMH) has been reported as
an even more reliable test for identifying GTCTs (Ball et al, 2013), although
results of the assay can still be inconclusive. Testosterone assays have
historically been employed to confirm the diagnosis of GTCTs but are of more
limited use because only ~55% of GCTs secrete this hormone, and most of
the affected mares will in any case show stallion-like behaviour. Many
practitioners combine measurements of testosterone, oestrogens (also
secreted by some GTCTs) and progesterone, where levels of the latter are
usually basal in the case of a GTCT since very few secrete progesterone and
the ovary contra-lateral to the tumour is usually inactive. Furthermore, one of
the alternative causes of gross ovarian enlargement, the anovulatory or
haemorrhagic follicle, usually luteinizes in part, secretes progesterone and will
respond, at least temporarily, to PGF2a treatment. PGF2a administration can
therefore be an aid to differential diagnosis of a GTCT from an anovulatory,
haemorrhagic follicle.
Endometrial biopsy
In terms of arriving at a prognosis for the likely success of breeding an aging
or problem mare, endometrial biopsy is an underused but useful tool. It gives
valuable information about the endometrial architecture, and in particular the
amount of chronic damage present in the form of fibrosis, gland nests and the
dilation of glands and lymphatic vessels. While the detection of multiple
endometrial cysts with the scanner suggests a possible problem, only a
biopsy can quantify its significance. Ideally, a biopsy should be taken when
the mare is in dioestrus since this is most representative of the situation
during pregnancy, is standardized and easiest for the histologist to assess; in
addition, after collection of the biopsy the mare can be treated with PGF2a so
that she returns to oestrus and clears up any contamination. The biopsy
forceps are usually introduced blindly through the cervix with the aid of a
sterile gloved hand and then guided per rectum to the base of one of the
uterine horns, the normal biopsy site. The sample is taken by pushing the wall
of the uterus into the side of the open jaws of the forceps from above, this
ensures that the bite will not go right through the uterine wall. The biopsy
should be fixed in Bouins’ solution (preserves endometrial architecture better
than formalin) and sent to a laboratory for processing. The scoring system is
based on the scheme developed originally by Dr R. Kenny and uses the
grades I, IIa, IIb and III. Grade I is a good healthy sample and, if the mare gets
pregnant, she is expected to have a > 80% chance of carrying that pregnancy
to term; Grade IIa implies scattered areas of inflammatory cells or mild
fibrosis, and is associated with a 50–80 % chance of carrying a pregnancy to
15-‐18
February
2016
East
London
Convention
Centre,
East
London,
South
Africa
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