Veterinarians and breeders can now detect pregnancy in mares using an ELISA (enzyme-linked immunosorbent assay) test that detects estrogen molecules in a mare's blood sample and is cheaper and easier to perform than an ultrasound.

BioTracking, a company founded by Garth Sasser, PhD, a professor of animal science at the University of Idaho, recently introduced a test that can detect pregnancy in mares with high accuracy at 70 days post-breeding and two weeks before foaling. According to Jeremy Howard, sales manager at BioTracking, breeders and veterinarians can draw blood from mares and send samples to BioTracking's lab. Earlier this year, the company released a similar test that aids in tracking the pregnancy.

The specific molecules detected by the blood test are estrone sulfate, a hormone produced in high concentrations by the placenta and fetus that is present in a pregnant mare's blood and urine.

During the first month of pregnancy the blood level of estrone sulfate conjugate is very low (below 5 nanograms /mL). It rises between Days 38 and 42, due to estrogen produced by the corpus luteum (what remains of a follicle after an egg has ovulated and which produces the hormone progesteron) in the ovary. Estrone sulfate concentration in blood plasma gradually increases to a relatively high level (12 ng/mL of plasma) by Day 70. The hormone concentration continues to increase and remains significantly higher than in nonpregnant mares