MRLS Research Stresses Possible Convergence of Climate, Management Factors

The cases of mare reproductive loss syndrome (MRLS) that Lexington, Ky., experienced in 2001 were a symptom of many issues converging, according to laboratory medicine specialist Jennifer Taylor of Melbourne, Australia. Taylor presented her findings in a seminar at the University of Kentucky's Gluck Equine Research Center on June 30.

"This type of abortion happens all over the world and for a variety of reasons," said Taylor. "Only by understanding it can we prevent it from happening again."

Taylor advised looking at the mares and the pastures for answers. She was contracted by a large stud farm in Lexington to set up a $100,000 U.S. laboratory to monitor all breeding stock in 2001 when $336 million worth of foals aborted. All scientific work to date has focused on the overwhelming presence of Eastern tent caterpillars In her study she created extensive equine blood profiles on affected mares, zeroing in on high levels of blood urea nitrogen (BUN) in all cases.

"Nitrogen is used to build protein, and the excess is then excreted from the body via the liver and kidney," she said. "When it cannot be excreted quickly enough, it will form toxic ammonia which accumulates in body fluids in such areas as the brain, eye, pericardium (the fibrous sac that surrounds the heart), and amniotic fluid, causing hypoxia (lack of oxygen) and a decrease in blood flow in tissues."

According to Taylor, during the MRLS occurrence in 2001, abortions occurred as a result of the extreme changes in weather, specifically a frost (also present in the MRLS cases of 1980/1981) which shut down the grass photosynthesis. This caused the gut flora of horses grazing affected pasture to produce excess. Taylor found that mares with limited access to turnout in 2001 fared better than those that were out on grass entirely. Other causes of this type of abortion, which Taylor noted is experienced all over the world, ranged from pasture management--in particular, fertilizing techniques that could have included the chemicals sprayed to eradicate caterpillars.

"We need to start looking at mares and pasture management through different eyes," she said, noting that her research including the biochemistry and hematology profiles on these mares before and after the event of 2001 brought to light a previously unrecognized mechanism of abortion in the mare.

This information is not new but has not previously been considered applicable, according to Taylor, and she cited a multitude of scientific studies in horses, cows and other animals over the years that showed high levels of ammonia adversely affect embryos and fetal development, cause abortions, and can result in difficult conception.

Taylor recommends more research to pinpoint how we can keep these tragedies from occurring again. "We're getting on to 10 years now and I don't think people are happy that they don’t have an answer yet."

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Jeannie Blancq Putney

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