Mares bred early in the time period were overwhelmingly more susceptible to losing their foals. Of those bred from February 9-17, a whopping 77% are no longer in foal. For the period of February 18-March 3, 49% had lost their foals. From March 4-17, that number slipped to 29%, and from there decreased in two-week periods to 26%, 11%. Of those mares bred from mid-April to mid-May, only 3% were no longer in foal."This dovetails with the theory of tent caterpillars causing the syndrome if the insult occurred in mid-April and it then took a week to be causative," said McDowell. "The vets started checking these mares in earnest in early May, and that would be consistent with the high-loss numbers for those mares bred in February."
A reproductive study examining the breeding records of four Central Kentucky Thoroughbred farms reveals that nearly 30% of mares bred between early February and early May 2001 who were declared at one time to be in foal, lost those foals.Dr. Karen McDowell, associate professor at the University of Kentucky's Gluck Equine Research Center, reported the results of the study at the meeting at Keeneland Thursday dealing with mare reproductive loss syndrome.The study encompassed a total of 487 mares bred between February 9 and May 2, and was accomplished with the assistance of the Jockey Club's information system. As of May 15, 347 mares, or 71%, remained in foal, while 140 mares, representing 29%, were no longer in foal. The study also revealed that the mean loss date for the mares was 60 days.