Pregnancy Detection
Efficient management of reproduction in the mare requires the detection of pregnancy after artificial insemination or natural breeding. There are a variety of methods that may be used to detect pregnancy in the mare. We will be covering hormonal measurement, behavior changes, rectal palpation and the use of the ultrasound.
Early pregnancy detection is necessary to successfully manage the mare through the 335 - 342 day gestation. Management of the mare during pregnancy will involve feeding, worming and vacinations specific to the pregnant mare. These however will be covered in a later chapter. During pregnancy detection it may also be learned that twins are present. We will discuss what should be done with twins later in this chapter. With the advent of modern technology it is now possible to detect pregnancy very early. However, since early embryonic death (EED) is quite common in the mare, periodic evaluation of pregnancy status is required. The causes of EED include uterine infections, hormonal imbalances, pathology of uterine glands, genetic abnormalities or may be unexplained.
After fertilization of the oocyte, it is essential that the mare recognize she is pregnant. There are at least three distinct points of early recognition of pregnancy by the mare:
- 48 hr after conception the pregnancy specific protein, Early Pregnancy Factor (EPF) is produced.
- At 5-6 days after ovulation only embryos move from the oviduct into the uterus. Unfertilized eggs remain in the oviduct and degenerate.
- At 12-16 days the embryo produces a substance which blocks the production of uterine PGF2a. In a non-pregnant mare, this PGF2a causes the normal regression of the CL and the drop in progesterone. The substance in the pregnant mare is refered to as antiluteolytic because it prevents regression of the CL and maintains progesterone production.
Even though the mare can detect chemical changes associated with pregnancy by day 12, reliable commercial tests have not been developed to detect any of these compounds or events. Emphasis has not been placed on developing such a test as most failures in development occur after fertilization and before day 12. Pregnancy detection tests before day 12 would be subject to large amounts of false positives in that mares would be said to be pregnant but would later be found to be not pregnant.
