Careful fetal and placental monitoring from the very beginning of the pregnancy can greatly improve the mare’s ability to carry the foal to term.
1. Progestagen assays alone will not confirm pregnancy in mares. Progestagen assays will tell if the mare is producing enough of these hormones to maintain the pregnancy.
2. BET prefers to test for PMSG (pregnant mare serum gonadotropin) also known as eCG (equine chorionic gonadotropin), when mares are between 45 and 90 days pregnant. This test has approximately a 5% false negative rate and a 10% false positive rate. PMSG values above 1 I.U./mL are considered positive; however, normal values are between 10 and 100 I.U./mL. Low levels of PMSG reflect fetal rejection by the mare. Mares which are below 10 I.U. and pregnant may be at risk of losing the pregnancy unless maintained on progestin therapy. Normal PMSG concentrations are 10-100 IU/mL with a peak at approximately 60 days of gestation. Some donkeys & miniature donkeys may not produce PMSG at all. Thus, this test is not very reliable in donkeys.
3. From 110 days to term, total estrogens assays are used to confirm pregnancy and monitor fetal viability. This test includes Estrone Sulfate and is approximately 99% accurate. Total estrogens assays work best between 100 days and 2 weeks prior to foaling. After 110 days of gestation Total Estrogens levels should be over 200 pg/mL; between 150 and 300 days it should be over 1,000 pg/mL. Low estrogens concentrations reflect fetal distress. Values will be similar for miniature mares, but different for donkeys and mini donkeys.
Approximately 2 weeks before foaling, total Estrogens levels begin to fall rapidly to approximately 300 pg/mL at foaling.
Progestagens rise and Total Estrogens fall prior to parturition in the mare. The rapid rise in Progestagens is thought to be due to Corticoid secretion by the fetus. The typical relationship between Progestagens and Total Estrogens prior to foaling is shown below. Not all mares follow this pattern. Alkaloids in the fescue and other plants prevent the dramatic rise in the Progestagens. The mechanism of this action is unknown.
|Days post ovulation||ng/mL|
|0||Less than 1.0|
|2||1.0 – 3.0|
|5 – 12||4.0 – 10.0|
|15 – 18||3.0 – 10.0|
|21||3.0 – 10.0|
|25 – 30||2.5 – 10.0|
|45||4.0 – 10.0|
|60||4.0 – 15.0|
|80 – 315||5.0 – 10.0|
|316 to term||20.0 – 40.0+|
|DAYS||PROGESTAGENS (ng/mL)||TOTAL ESTROGENS (pg/mL)||TOTAL T4 (ng/mL)|
|0 days post-ovulation||<1.0||less than 200||12.0-25.0|
|2 days post-ovulation||1.0-3.0||less than 200||12.0-25.0|
|5-90||4.0-10.0|| less than 200||12.0-25.0|
|100-110||4.0-10.0||less than 200||12.0-25.0|
|150-320||4.0-10.0||greater than 1000||7.0-25.0|
|post foaling||<20.0||less than 200||12.0-25.0|
NORMAL LEVELS OF TOTAL ESTROGENS DURING PREGNANCY IN THE MARETotal Estrogens test is valid after 110 days of pregnancy and its levels reflects the viability of fetal-placental unit. Normal Total Estrogens in donkeys are approximately 20% lower than Normal Total Estrogens in horses.
Approximately 2 weeks before foaling, Total Estrogen levels fall rapidly to around 300 pg/mL.
|DAYS OF PREGNANCY||TOTAL ESTROGENS
|BARREN / OPEN||2-200|
|90 - 110||205|
|110 - 120||356|
|120 - 130||469|
|130 - 140||857|
|140 - 150||1,040|
|150 - 320||GREATER THAN
MEAN CONCENTRATIONS OF PROGESTINS AND TOTAL ESTROGENS PRIOR TO BIRTH
|DAYS OF PARTURITION||PROGESTERONE (ng/mL)||Total Estrogens (pg/mL)|