Hemlock, bacteria spark new MRLS dialogue

Cleveland-Nearly a year has passed and the 2001 Mare ReproductiveLoss Syndrome (MRLS) still evokes impassioned discussions of its cause,which was never conclusively determined.

New talks at meetings in central Kentucky and Clemson University pitan alpha streptococcus organism against a hemlock theory, the latter ofwhich had been swiftly denied.

About 350 veterinarians and equine professionals met Feb. 4 in Lexingtonat a meeting hosted by the University of Kentucky College of Agricultureand the Equine Maintenance Managers Association to probe further the circumstantialevidence of MRLS.

Dr. Stuart Brown of Hagyard-Davidson-McGee Associates, presented dataon 3,000 broodmares that lost foals early in their pregnancies.

Broodmare findings

"What led me to investigate the broodmare population was all thefetuses that were falling out in front of me," he explains. "Mareswithin the 60-70 day window presented with expelling fetal membranes anda mucoidic discharge."

In early May, at the syndrome's peak, Brown took uterine cultures onmares that had early fetal loss and discovered two bacterial species: AlphaStreptococcus and Actinibacillus sp. organisms. About 65 percent of samplesdisplayed alpha bacteria; 20 percent showed actinobacillus.

Although Brown says he is not implying these bacteria are the cause,he thinks they relate to MRLS.

"Finding these two organisms is a striking occurrence. Alpha streporganism is not something you'd commonly expect to find," says Brown.

Similar data

Brown soon learned his findings matched those of Dr. Mike Donahue, supervisor,bacteriology laboratory at the University of Kentucky Livestock DiseaseCenter. Donahue took samples of 500 late-term fetuses in 2001- 70 percentof tissues from the lung or umbilical cords contained one or both of thesame bacteria. Donahue then froze 380 samples for further study.

Two ongoing goals for Donahue: 1) Determine the exact bacterial speciesinvolved. "It doesn't look like they fit taxonomy-wise any of theknown streps and actinobacillus," he says, and 2) Find the source- whether it is environmental or internally existing in the horse. "Thebacteria are probably normally found in the upper reproductive tract orthe intestinal tract, but we haven't looked for them."

Donahue was in Kentucky the last time a similar mare reproductive catastropheoccurred in the early 80s. "If I can get ahold of some of the strainsof bacteria that occurred 20 years ago, I would compare them. The outlookis not very great."

Adds Brown, "In 1981, people thought these organisms were secondaryinvaders. That may prove true, but we better make damn sure that's whatwe really think is occurring, so we don't miss a key ingredient that mightsteer us to figure it out. Finding out the origin of the organisms mightcarve out the pathophysiology of the whole syndrome."

Revisited theory

In a separate meeting at Clemson, Feb. 8, Dr. Dee Cross, professor ofanimal and veterinary sciences, presents telling evidence. Remember thepoison hemlock idea?

In the aftermath of MRLS, Cross and other researchers collaborated todetermine the differences between control pastures in Kentucky with no abortionsand affected pastures. They created a checklist of potential MRLS triggers:external ergots (fungus with high levels of toxic alkaloids); pasture/forageplants; Zerealonone (fungal mycotoxin); internal ergots; cherry trees; feed;and hay. All items turned up negative, with little exception.

Researchers then began checking for plants near fencerows or tree enclosureswhen they found poison hemlock. "Not only was hemlock present on affectedfarms, but there was evidence of consumption," says Cross. "Correlationshowed an extremely high relationship." (T < 0.0001: less than 1in 10,000 chance that poison hemlock was not related to the problem, accordingto Cross.)

In all, 27 of 28 MRLS-affected farms, had hemlock presence and consumption.In 10 pastures that did not exhibit problems, there was no sign of hemlockconsumption.

Cross then teamed with an expert in poison hemlock, Dr. Kip Panter, USDA-ARSpoisonous plant lab, Utah. They sent samples from foals and plant tissuefor assay.

"Plant tissue came back with toxic piperidenic alkaloids as suspected.But samples from foals and some serum samples from mares detected no levelsof the alkaloids," he says.

These alkaloids have a nicotine-like effect, says Cross, who adds theyare known to have caused abortions in several species, but have not beenresearched in horses.

Researchers then dosed two non-pregnant horses with poison hemlock todetermine depletion rate (how soon after consumption it can be detectedin the blood.) Hemlock reportedly cleared the horse's system in 50 hours.

"Unless you took a blood sample or had a foal exposed within thelast 50 hours, you would never pick it up," says Cross. "Therewas no chance for us to have picked up the alkaloids."

If a future study proposal receives funds, Cross says 14 pregnant mareswill be dosed at toxic levels to see if it causes abortion.

Piperidenic alkaloids

Research indicates that young, tender, as well as stressed poison hemlockhas a very high level of piperidenic alkaloids, says Cross. In early spring,hemlock has high sugar content and is more palatable.

He suggests horses consumed hemlock following the unusual weather.

The reaction to the hemlock theory from scientists at the Gluck Center- "I'd rather not comment on how it was received by ... the Universityof Kentucky, which walked way out on a cherry tree limb," he says.

Although Dr. Roy Smith, of the UK diagnostic laboratory, saw the numberof farms that showed signs of hemlock consumption as brow-raising, he quicklyadded that hemlock is "highly improbable as a cause," accordingto a Bloodhorse.com report. He based it on a sampling of 50 fetuses examinedin 2001 that found no evidence of hemlock consumption.

"Smith based his comment on the fact that samples didn't show anyof the residues," answers Cross. "That's why we did the researchto show him you would not have found any residues unless we had taken asample within 50 hours of consumption."

Cross stands by the hemlock theory. "We think this is the totalcause. It is likely exacerbation from other things(the freeze), but thiscan cause those abortions. Also, literature is clear that this plant isvery addictive. Reports show animals have been addicted and want to consumeit again."