March 5, 2003 | By: Laura Skillman

Kentucky hay suffered an image problem in 2001 because of fears over its possible relationship to foal losses in pregnant mares. That image problem is going away thanks to research efforts showing it was not the problem.

Hay, particularly alfalfa hay, is an important staple in the diet of horses in the commonwealth making the horse industry a key customer of the state’s alfalfa hay producers. However, when horses began suffering fetal losses in large numbers due to an unknown source in the spring of 2001, a finger was prematurely pointed at hay as a possible source of the problem.

Mare Reproductive Loss Syndrome resulted in devastating losses to the state’s horse industry with an estimated loss of $400 million in future sales because of fetal losses.

“It was literally a disaster,” said Jimmy Henning, a University of Kentucky College of Agriculture forage specialist and a member of the MRLS investigation team.  “Frankly, we didn’t know what was going on.”

Researchers began looking for a cause to this syndrome and at least one consultant proclaimed he would not feed any hay grown in Kentucky. Concern by horse owners and farm managers prompted many to turn to other sources for hay in 2001.

“It really negatively affected the alfalfa hay market in Kentucky,” Henning said.

Many alfalfa producers reported not being able to sell their first cutting of hay to broodmare operations and having to seek out alternative markets. Subsequent hay cuttings were tested to prove their safety.

After substantial testing by UK specialists with the assistance of horse farms in central Kentucky, veterinarians and others, it was determined there is a correlation between Eastern Tent Caterpillars and MRLS, Henning said.  It is not yet known what about the caterpillar causes the problem, he said. Research is ongoing to try to determine what it is about the caterpillar that results in MRLS.

Henning recently updated state alfalfa producers at the 23rd annual Kentucky Alfalfa Conference on the research that has occurred and continues to occur into this syndrome.

Hay became an early suspect because of fungal mycotoxins – a secondary fungus that can be brought on in pastures and hayfields by environmental stress such as late frost and drought, he said. Fungal mycotoxins, if present in fields or hay, can cause some of the symptoms displayed in mares in the spring of 2001.

UK, with assistance from the Kentucky Department of Agriculture, began by testing samples of hay made prior to the Kentucky Derby for mycotoxins.

“All were negative, every single one of them,” Henning said.

In 2002, pastures and hayfields were monitored and found to be nutritionally safe in nitrate levels, yeast and mold and mycotoxin values were generally zero across the entire sampling period, Henning said. This information along with additional research by two UK scientists directly implicating the eastern tent caterpillar as the likely cause of MRLS indicates that Kentucky grown hay is not a risk factor for the syndrome, he said.

Henning told hay farmers need to be sure their hay is clean of caterpillar larvae. They also need to be aware of the research that was conducted on hay in order to counteract any lingering questions about the safety of Kentucky hay, he said.


Jimmy Henning, 859-257-1846