Page 533 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

508 CHAPTER 2

VetBooks.ir Diagnosis the reproductive tract and serial plasma progester-
one samples help differentiate this condition from
Repeated reproductive examinations of the mare,
including rectal and ultrasonographic examinations
condition and nutrition plus decreasing stress will
of the ovaries and reproductive tract plus vagino- other cyclic abnormalities. Improving the mare’s
scopic examinations of the cervix, should be able to help some mares, while intramuscular prostaglandin
identify physiological oestrus changes. Serial plasma is effective if there is a persistent CL.
progesterone samples (every 4–5 days) should iden-
tify when the mare enters oestrus (plasma proges- Aetiology/pathophysiology
terone <3.18 nmol/l [1 ng/ml]) except for early in This problem probably has a number of causes
the year when winter anoestrus may still be present. related to photoperiod early in the year, poor body
A careful and imaginative approach to teasing with, if condition and nutrition, and stress conditions. The
necessary, restraint of the mare, plus acute observa- relationship to lactation per se is questionable. It
tion by the teasing personnel, may sometimes allow may be related to persistence of the CL (prolonged
recognition of some oestrous behavioural changes. dioestrus) after a normal foal heat or, more rarely,
complete ovarian shut down and anoestrus after
Management parturition.
AI can be used where this is permitted, but accurate
timing is not helped by the lack of oestrous behav- Clinical presentation
iour and reliance has to be placed on serial reproduc- Most commonly there is a normal foal heat, both
tive examinations. Careful and persistent teasing can behaviourally and physiologically, and then the
help relax mares and many will show oestrous behav- mare does not return to normal cyclic behaviour at
iour eventually. Care is required to protect the stal- the normal interval. Often the foal heat will be later
lion and personnel present at covering and in some than expected. Rarely, the mare goes straight into
cases, the use of sedation is necessary together with anoestrus post partum. It appears to be more com-
other forms of restraint (e.g. twitch, hobbles). mon in mares that foal in the early months of the
breeding season (February/March in the northern
Prognosis hemisphere) and in older mares in medium to poor
The prognosis is fair with persistent and effective body condition. It may be 1–3 months before mares
teasing. Missing the oestrus and letting the mare return to normal cyclic activity.
come back into season may improve the behaviour
in some cases, particularly those mares with a foal Diagnosis
a foot. A full reproductive examination should be under-
taken, including rectal palpation and ultrasono-
POST-PARTUM OR LACTATIONAL graphic evaluation of the ovaries and uterus, plus
ANOESTRUS plasma progesterone samples. Those cases with per-
sistence of the CL will have raised progesterone lev-
Definition/overview els and clinical signs as already noted (p. 408). Those
This is an uncommon condition less related to lac- mares that enter true anoestrus will have plasma
tation than to early foaling dates (decreased photo- progesterone concentrations <3.18 nmol/l (1 ng/ml)
period), poor body condition or nutrition, and and small inactive ovaries, plus a flaccid uterus and
stress. Originally, it was thought that there was a partially open cervix. Any nutritional and/or medi-
persistence of the CL after a normal foaling heat, but cal condition leading to poor condition and health
now it is generally considered to be a true anoestrus requires detailed investigation.
and ovarian shut down. Mares either demonstrate a
normal foal heat and then do not cycle for between Management
1 and 3 months or, occasionally, do not cycle at all It is essential to identify these mares early as
post partum. Rectal palpation, ultrasonography of treatment of chronic cases can be unrewarding.