EQUINE REPRODUCTION

Pregnancy, ovulation, and ovarian function in dry or lactating equines can be determined by rapid, inexpensive, laboratory tests for the hormones "progesterone" and "estradiol." These results should be used in conjunction with your normal veterinary services, not as a replacement for your veterinarian.

• Only a small amount of blood is needed (1mL). Results are available the day after we receive the sample.
• Samples for pregnancy testing using estradiol or progesterone may be sent by First Class mail. Please use a padded envelope or box and PLASTIC blood containers. Do not send syringes or glass tubes. We will give you the necessary plastic sample tubes.
• If estradiol is to be used for ovarian function testing, please call for shipping information. The hormone concentrations involved in this use for the test may be much less than those for a pregnancy/non-pregnancy test. Therefore, the sample needs to have special care in transport.

• Shortly after ovulation, a Corpus Luteum (CL) forms and produces progesterone. The progesterone concentration remains high (more than 1.5ng/mL) throughout pregnancy. A non-pregnant mare has progesterone concentrations which rise and fall as she cycles. Her progesterone concentration will be low when she is about to ovulate and is normally in heat. Therefore, a non-pregnant mare will have a low progesterone concentration every 19-24 days. A mare who is both pregnant and in heat will have a high progesterone concentration.
• A pregnant mare begins to produce estradiol (also called E2) about 60-70 days of gestation. The E2 concentration peaks and remains high (usually more than 800pg/mL) by 140 days of gestation.

• A low progesterone concentration (less than 0.1ng/mL) 19-24 or 44-48 days after breeding indicates that the mare is not pregnant. A mare cannot carry the fetus if the progesterone is low.
• A high progesterone (more than 1.5ng/mL) 19-24 or 44-48 days post breeding indicates that the mare is pregnant at the time that the sample was taken. Most pregnant mares will have progesterone concentrations of greater than 3.0ng/mL.
• A high estradiol concentration (more than 350pg/mL) more than 140 days post breeding indicates that the mare is pregnant, and that the pregnancy is proceeding as it should. Often, clinicians will monitor both progesterone and estradiol throughout problem pregnancies. Progesterone and E2 come from different biochemical pathways in the mare and fetus.

• Incorrect estimation of the time of estrus and ovulation, embryonic loss, and ovarian disorders all may produce a "false positive" result. The samples must be taken at the correct time of gestation: Progesterone: 19-24 or 44-48 days. Estradiol: more than 80 days.

• Progesterone can be used to determine if a mare is cycling at all.
• Silent heat can be detected, since the progesterone level should always be low during estrus. A low (0.1ng/mL or less) progesterone is required fro ovulation.
• A mare who shows signs of heat, but is not about to ovulate can be identified and treated.
• Progesterone concentrations of 1.5-3.0ng/mL seem to be associated with an increased risk of abortion.

• The E2 concentration should rise sharply just prior to ovulation. If it does not, there may be concern about ovarian function.
• The E2 concentration in a mare can be determined as an indicator of ovarian function in a non-pregnant mare.

RMIL also offers veterinary endocrine testing for many other species.

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Updated: 27 March 2011