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Horses and Drooling

The Question

A horse owner sent me an e-mail expressing concern about the excessive salivation noted in her 3 horses this year.

My Answers

The slobbering is associated with black patch disease caused by Rhizoctonia leguminicola. The specific causal agent is slaframine which is an indolizidine alkaloid and a metabolite of Rhizoctonia leguminicola.  Conditions were right for its development this year, rainy conditions and high humidity.

Interestingly, the compound does decrease in red clover hay while in storage.  One study sites a decrease in 10 months of storage from 50-100 ppm to 7 ppm.

Reading about the associated biological effects in Peter Cheeke's "Natural Toxicants in Feeds, Forages, and Poisonous Plants" book makes one raise their eyebrows as to why we even use potentially infectious clovers at all.  In cattle, concerns include excessive salivation, eye discharge, bloat, frequent urination, watery diarrhea, reduced milk production, weight loss and abortion.  Other things noted include increased pancreatic flow, bile flow, and gastric acidity, and decreased heart rate, cardiac output, respiration rate, body temperature, and metabolic rate.  With use of guinea pigs as an assay animal, the LD50 was less than 1 mg of slaframine/kg (1 kg=approximately 2.2 lbs.) of body weight.

Applying some mathematics and assuming a guinea pig and horse have a similar lethal dosage response, a 100 ppm slaframine forage fed to a horse consuming 25 lbs. of dry matter is equivalent to 11.35 mg of slaframine.  Assuming the horse weighs 1000 lbs., this is a dose of .025 mg/kg of body weight, much less than the lethal dose rate found in the guinea pig experiment.

So do you get rid of the clover?  If you truly don't enjoy your horses because of the slobbers, maybe so.   Keep in mind, that you may not see slobbers to the extent seen this year for many years.  I personally am not convinced that one reduces use of clover because of all the nasty things described in Cheeke's book unless you have seen these symptoms, too.   Many of the things we enjoy in our own diet have natural toxicants in them, too, but we suffer no consequence because of amount consumed and/or dose present in the food item.

You need to balance the positives and negatives for the use of red and white clover in your pasture.  There are many positives  (forage quality improved, more summer pasture with use of red clover, no N fertilizer needed for the grass component of the pasture)  when legumes are a part of the pasture.  Is this worth more than the negative issue of slobbers?   This is a judgmental call that I think you need to consider.

Maybe alfalfa should be the legume of choice when seeding your next hay and pasture fields?

Back to Forage Issues

Keith Johnson
Professor of Agronomy and Forage Crops Specialist
1150 Lilly Hall of Life Sciences
West Lafayette, IN 47907-1150
phone: 765-494-4800
fax: 765-496-2926



For more forage information contact Dr. Keith Johnson: johnsonk@purdue.edu

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