"We can prevent mare reproductive loss syndrome (MRLS) as we experienced in 2001 and 2002 by keeping horses away from caterpillars," said Bruce Webb, PhD, a University of Kentucky (UK) researcher who has been studying the condition that terminated thousands of mare pregnancies in Central Kentucky and nearby states. The pervading theme at a Nov. 30, 2005, meeting at Keeneland in Lexington, Ky., was that more needs to be understood before researchers can effectively intervene in the MRLS disease process.

The scientists presented 14 months of Kentucky Thoroughbred Owners and Breeders (KTOB) Foundation-sponsored research material and suggested future study avenues. Topics included:

Eastern Tent Caterpillars (ETC)--Researchers suspect that small lesions created in the mare's gastrointestinal (GI) tract by the caterpillars' setae (hairs) might allow bacteria to enter and circulate in the body to somehow reach the fetus and ultimately cause abortion. UK's Karen McDowell, PhD, David Horohov, MS, PhD, and Neil Williams, DVM, PhD, used skin tests and histologic sampling to find that setae did not modify the mare's immune response.

Webb said to keep pregnant mares off pastures with caterpillars for eight weeks after trees lining the pastures are sprayed with a caterpillar insecticide. Also, introducing a caterpillar virus early in the ETC season could dramatically decrease ETC numbers.

Bacterial Culprits--Newman identified levels of bacteria thought to cause MRLS in different parts of the mare's digestive tract. The numbers of MRLS-associated Streptococcus bacteria increased when mares ate ETC. Newman matched the DNA of suspect strains of bacteria in the mouth of a mare and the bacteria that infected her fetus during MRLS. He wants to know why these bacteria are involved, how they get from the GI tract to the fetus, and why antibiotics don't work in these mares.

Studying the Fetus In Utero--Cornell University's Don Schlafer, DVM, MS, PhD, Dipl. ACVP, ACVM, ACT, has placed catheters in the blood vessels of unborn foals and special probes around the mares' uterine arteries and umbilical arteries (vessels that send blood from the fetus to its placenta). He has monitored the blood flow between the fetus and placenta and from the dam to the pregnant uterus as the mare rests and exercises, and he has recorded blood flow decreases when the umbilical cord is kinked or folded, simulating cord tension, which can cause abortion in mares.

Schlafer is seeking funding for the research, which could be used to investigate fetal responses to viruses, bacteria, and other microbes that find their way to the pregnant uterus, as in MRLS. This could also help scientists explore possible immunization of the fetus in utero. More information: www.TheHorse.com/emag.aspx?id=6353.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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