OESTRUS SUPPRESSION IN THE MARE
Anne Josson, Dr Med Vet, DACT
VetAgro Sup, 1 Avenue Bourgelat, 69280 Marcy L’Etoile, France.
INTRODUCTION
Before discussing oestrus suppression in the mare, I want to highlight some
important points in the normal cycling mare in the hope to better understand as to
why we can or cannot suppress oestrus in the mare. The mare is a long-day,
seasonally polyestrous animal with an oestrous cycle of approximately 21 to 23 days
including behavioural oestrous signs lasting 5 to 7 days. Around 48 hours post
ovulation, the progesterone levels increase sufficiently (> 1 ng/ml) to stop oestrous
behaviour.
Mares are unique, when compared to other domestic animals, in that many of these
seasonally anovulatory (and ovariectomized) mares exhibit paradoxical oestrous
behaviour associated with hormone secretion from the adrenal cortex. (5, 6) The
intensity of this type of ‘unseasonable’ oestrous behaviour looks similar to the
behaviour expressed by intact cycling mares during the beginning of the oestrus
cycle or just after ovulation, which is less intense than the behaviour displayed near
ovulation. The fact that mares can be receptive to stallions during winter anoestrus
can explain why simply suppressing ovarian follicular activity may not ensure the
elimination of oestrous behaviour. Oestrogens can also be produced by the zona
reticularis of the adrenal gland.
Indications:
The primary indications for suppressing oestrous behaviour include cycle-related
behaviour or performance problems and pain or colic during oestrus. Approximately
90% of the veterinarians have the impression that the oestrous cycle has an impact
on the performance of mares. The most important clinical oestrus signs reported by
the owners to have an effect on the mare’s performance is:
- attitude change, mare is ‘distracted’
- tail swishing
- difficulty to train or handle
- squealing
- excess urination
- kicking, being aggressive
- reduced athletic performance due to lack of concentration
It is important to note that some of these difficult behaviour patterns such as
submissive behaviour, urogenital discomfort or stallion-like behaviour, displayed by
these ‘so called’ problem mares, are blamed to be associated with oestrus, but are in
fact not at all signs of oestrous behaviours. (9, 10) Leaning away from perceived
threats, swishing tails and actively squirting urine can easily be confused with
oestrous behaviour inn the mare. (10)
My scoring system for heat detection in the mare is:
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
16