Page 535 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

510 CHAPTER 2

VetBooks.ir Eventually, the follicle may luteinise and the mare but feels firmer and within the ovarian structure.
The contralateral ovary is normal and the mare will
will stop oestrous behaviour. The luteinised follicle
may have a normal lifespan or be prolonged, lead-
ciently to produce enough progesterone to inhibit
ing to persistent dioestrus. Mares with anovulatory continue to cycle unless the HAF luteinises suffi-
follicles may accept the stallion, but as no ovulation the return to oestrus. Anovulatory follicles will usu-
occurs they do not conceive. ally regress over a period of 1–2 months, with the
ovary returning to a normal size.
Differential diagnosis
Ovarian tumour, especially GCT; transitional ova- Management
ries; ovarian abscess. Many of these mares will not respond to treat-
ment, but will (eventually) spontaneously resolve the
Diagnosis problem. If the follicle luteinises, it may respond to
Repeated rectal palpation and ultrasonography of the exogenous prostaglandins. Recurrence at subsequent
ovaries are essential to identify and follow-up mares oestrous periods can occur. Occasional cases will
with anovulatory follicles. Affected follicles may ovulate if diagnosed in the early stages of becom-
develop gradually into very large structures (>10 cm ing an HAF and are treated with exogenous hCG or
in diameter), but they do not ovulate (Fig. 2.120). GnRH. Matings on spontaneous or induced ovula-
They have a variety of ultrasonographic appearances tions in these cases are rarely successful as the oocyte
within the follicle including free-floating focal echo- ovulated is often degenerate and non-viable. The use
genicities, bands of tissue, haemorrhagic structures of prostaglandins to induce luteolysis may increase
and outer rims that become more echodense with the risk of HAF formation and should be avoided in
luteinisation. The ovary becomes enlarged on rectal the early and late breeding season. Caution is needed
palpation, with a large follicle that does not progress in mares prone to this abnormality in the timing of
to normal maturational changes towards ovulation, breeding and insemination in order to avoid wasted
coverings and additional veterinary and semen costs.

2.120
Prognosis
The prognosis is good for return to normal cyclic
behaviour and ovulation over time, but short-term
delays to the breeding programme are an inevitable
consequence. Recurrence is quite common in some
mares. Further delays are possible if the follicle
luteinises and this CL persists, although these usu-
ally respond well to exogenous prostaglandins.

MASTITIS

Definition/overview
Mastitis is an uncommon condition, usually seen in
the post-weaning broodmare and occasionally in the
lactating mare. A variety of bacteria are involved, but
Streptococcus spp. are the most common. The mam-
mary gland is swollen, hot and painful on palpation
Fig. 2.120 Transrectal ultrasonogram of the ovary in the acute case, but becomes more fibrotic and
of a mare that is failing to ovulate. Note the very harder in the chronic form. The mammary gland
enlarged anovulatory follicle containing echogenic secretion changes nature and on cytology shows
material. (Photo courtesy Tracey Chenier) increased neutrophils and, occasionally, bacteria.