There are no significant differences between mares bred in Kentucky and mares bred in Florida, according to the preliminary results of a study that was designed to determine the effects of mare reproductive loss system (MRLS). Tom Riddle, DVM, and Kent Vince, DVM, of Rood and Riddle Equine Hospital near Lexington used ultrasound exams to compare the allantoic and amniotic fluids of the two groups. They also looked at fetal heart rates.

When MRLS appeared in Kentucky and other states this past spring, veterinarians observed that the allantoic and amniotic fluids of pregnant mares were flocculent (echogenic). It was known that this echogenicity was abnormal in mares less than 75 days because large numbers of mares had been ultrasounded at that stage of gestation in previous years. What was not known was the normal appearance of these fluids in the 75- to 150-day range.

The study found that in mares bred in Florida and Kentucky it was normal to have echogenic allantoic and amniotic fluids beginning at 85 days and continuing through 150 days (the oldest Florida pregnancy examined). Therefore, the appearance of echogenic fluid after 85 days should not be a cause for concern.

The heart rates of fetuses were studied because such rates are used to measure stress in unborn horses.Riddle and Vince ultrasounded 84 mares on six farms near Ocala, Fla., on Aug. 28. Dr. Chip Estes of Ocala organized the Florida portion of the study