Page 532 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.1 The female reproductive tr act 507

VetBooks.ir palpation reveals a non-pregnant uterus, which There is some controversy as to whether the mare
should be mated on this first oestrus or whether it
is firm and under progesterone stimulation. The
ovaries are active with follicular development.
injection and bred on the subsequent cycle.
Ultrasonography confirms no pregnancy, ovarian should be short cycled with another prostaglandin
activity and the presence of at least one CL (Fig.
2.119). Vaginal examination confirms a closed dioes- Prognosis
trus cervix. Sequential blood samples reveal persis- The prognosis for return to fertility is good except
tent high levels of progesterone. where chronic uterine damage is present.

Management BEHAVIOURAL ANOESTRUS
Intramuscular prostaglandin or its analogues are the
treatment of choice. A mature CL over 5 days old Definition/overview
will be lysed and the mare should come into oes- Behavioural anoestrus is defined as a lack of behav-
trus depending on the stage of follicular develop- ioural oestrus by the mare despite physiological
ment present in the ovary. If the ovary contains a changes of oestrus within the reproductive tract
larger follicle (>35 mm in diameter), ovulation may (‘silent heat’). It is possibly a behavioural or a psycho-
occur rapidly (within 48 hours) with a short oestrous logical abnormality. It is common in maiden mares
behavioural period. Where smaller follicles are or mares with a foal at foot. Diagnosis relies on con-
present, oestrus will usually begin within 2–5 days firming physiological oestrus without behavioural
and ovulation towards the end of the oestrous period. signs. Management relies either on AI or on careful
and persistent teasing to encourage mares to relax
and exhibit behavioural signs.
2.119
Aetiology/pathophysiology
Normally the physiological reproductive tract and
endocrine changes of oestrus are coordinated with
behavioural oestrus, allowing the mare to be recep-
tive to the stallion at the time of ovulation. In this
behavioural/psychological abnormality, mares do
not exhibit behavioural oestrus despite normal
physiological oestrus changes. Performance mares
previously administered anabolic steroids may also
exhibit problems of reproductive behaviour when
entering a breeding career, although this is a sepa-
rate iatrogenic condition.

Clinical presentation
This condition is most commonly seen in maiden
mares, particularly those that have had prolonged
athletic careers, mares with foals at foot, who are
very protective, and nervous mares of any age. It
is a particular problem where there is no access to
a teaser or stallion or where little time or effort is
Fig. 2.119 Transrectal ultrasonogram of the placed on the teasing process. The affected mare
ovary of a mare in persistent dioestrus revealing may show no signs of behavioural oestrus or it can
a mature corpus luteum (arrow). (Photo courtesy be aggressive towards the teasing stallion.
Tracey Chenier)