Hello Dr. Deb
I have 2 horses which I take out on varied trails from open hilly ground, river courses & old logging tracks in a pine/mixed native bush forest block. There is a particular place in the forest where the ground is wet all year round. The soil is clay. Now only one of my horses does this. He stops & fossicks the mud every so gently but intently. Then he bites up some of the mud, rolls it in the front of his mouth & gently licks it onto his front shins to his knees.He must be ingesting some of it. When he first did this, I checked for heat or discomfort in his feet & legs but everything seemed okay. This is the only place he does this on our outings. We go through this route maybe once a week & the other day, he very kindly lathered some of this mud onto my shoulder as well as his legs. I took it as a compliment.
I know that caolin in some soils are actively sought by various animals but I'm unaware what the clay in this patch of ground is providing for him. I follow Jenny Patterson's regime & the horses have had recent blood tests which came back almost text book levels. I wonder if there is simply a mineral leech from higher ground which is appealing to him or I am I being ignorant & inadvertently allowing my horse to indulge in something potentially harmful to his health.
Yup, I'd also say he's liking the taste of something in that particular patch of mud. If this is the only time he does it, then we can rule out dirt-eating as a stereotypy.
Unless you care to have a mineral profile run on this soil, it will be difficult to know whether it has some outstanding characteristic. If you're willing to be a little brave, and the soil does not contain manure, you can fossick around with one finger yourself and taste it. If it tastes salty, I'd say that's the most likely factor attracting the horse. If it tastes "dry", like it wants to suck up all the moisture on your tongue (and also if the soil color is yellowish rather than blueish) then indeed it does contain the alumino-silicate mineral kaolinite. If you smear some of it on a white card and get a bright indigo-blue color, it contains vivianite which is an iron phosphate. Beyond that, even as a trained geologist I'd need an assay.
And yes, I would definitely take your horse's efforts to share his "tasty mud" with you as a compliment. Cheers -- Dr. Deb