-
Larger than normal abdomen (esp. with a sudden onset)
Suspected twins
It is very valuable to perform repeat ultrasound exams on these high-risk mares:
- To measure the Combined Uterine Placental Thickness (CUPT)
- To evaluate the apposition of the placenta to the uterus
- To assess foetal position prior to foaling to eliminate a possible dystocia
- To assess foetal viability
- To detect foetal abnormalities
As the mare is the best incubator for the foal, I prefer to treat the foetus in the mare
rather then after foaling, if I can.
It is important to mention that the High-risk pregnant mare should be examined by a
veterinarian who is accustomed to evaluate mares in late gestation with both trans
rectal and trans abdominal ultrasound. Only when needed, the clinician should
perform a vaginal/speculum exam on a pregnant mare and be familiar with
assessing the integrity of the cervix.
A routine rectal exam on a late pregnant mare should include assessing:
- the tightness of the cervix
- the position of the foetus
- the size of the uterus
- the movement of the foetus (ballottement)
- palpation of the mare’s ovaries
- foetal eye measurement
ECG was used in the past to evaluate the foetal heart rate but that is nowadays
greatly replaced by trans abdominal ultrasound reliably performed after 90 days of
gestation. At this time the uterus drops over the pelvic brim and becomes visible from
the ventral abdomen. As the pregnancy progresses the foetus is found progressively
more cranial. If at all in doubt, it is important to exclude the presence of twins, as twin
reduction can still be accomplished at 116 days of gestation using trans abdominal
ultrasound guided an intra-cardial penicillin, local anaesthetic or potassium chloride
injection to eliminate one of the twins with about 50% success.
Equipment and Technique:
A routine trans rectal ultrasound scan provides access to the caudal aspects of the
gravid uterus and should always be performed at ANY stage of gestation. Up to 70 90 days the foetus is easily visible via trans rectal ultrasound only. For all trans rectal
U/S exams I use a ‘Mylab™One/Touch’, (easote) a handy portable ultrasound
machine with a 12-inch touch-screen display and a linear probe ranging from 5 to10
MHz.
For mares over 90 days pregnant, I still use the ‘Mylab™One/Touch’ (easote) for all
trans abdominal ultrasound exams with a macro convex ultrasound probe. It has a
wide range of frequencies, going from 2 to 8 MHz, with a depth of up to 23cm. If
possible, the pregnant mare is examined –not tranquilized - in her stall while eating.
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
252