Page 939 - The Veterinary Care of the Horse

pregnant mare. The rectal findings during early pregnancy are not always conclusive and

cannot eliminate the possibility of twin conceptuses.
VetBooks.ir ULTRASOUND SCANNING

This is the most commonly used method for pregnancy diagnosis and the assessment of early

foetal growth. It is performed from day 14 to 15 after ovulation (16 to 17 after covering)
onwards. It is the most reliable method of detecting unwanted twin pregnancies. To rule out
the possibility of twins, the mare is scanned at least twice in the early stages of pregnancy.

The procedure

To scan a mare during early pregnancy, an internal examination of the mare is required. To
ensure this is done safely for both the vet and the mare, it is important that the mare is

properly restrained. Stocks are ideal for this purpose. Electricity is required to power the
scanner and there must be a suitable area out of sunlight to view the scanner screen. To
perform the scan, the vet will remove the faeces from the rectum and introduce the probe.

This is then advanced until it lies over the uterus. It is moved from side to side, passing over
the uterine horns and the ovaries. An image is seen on the screen. If the mare is pregnant, the

embryonic vesicle appears as a distinct black sphere on the screen. When mares are
examined as early as day 14–15 after ovulation, they are checked again a few days later. The

embryo itself can be seen as a white speck within the circular black area between days 18 and
21 after ovulation. Even at this early stage, the pulsation of the heart is often visible. By day

26, the embryo is clearly visible as it lifts away from the wall of the vesicle and protrudes
into the lumen.

A third examination is ideally carried out around day 28 and before day 35 (Figure 19.18)
to ensure that the mare is still pregnant and to make certain that a twin has not been missed.

The optimum time for determining the gender of a foal in utero is between 60 and 65 days.