I thought it was done with a glove and leaving it for 30 minutes to see if sand collects in the fingers. However, our vet is due out this coming Friday and I intend to ask him. I'll let you know. Unless someone else has the answer before then.
You don't have to use a glove. I can't wear latex, so I only have opaque nitrile gloves around. So poop tests are in a glass jar. But you do want to get fresh manure that hasn't made contact with the ground. And let it sit for awhile so you can see the separation. I check mine once in awhile but have never found more than tiny amounts of sand/dirt in the bottom.
Sand colic and impactions most commonly occur in areas where horses graze on sandy soil pastures or eat off ground that is predominantly sand or fine gravel. To help determine if a horse has sand in his feces, owners can follow this simple recipe:
1. Place six fecal balls in a glass jar.
2. Fill the jar half full with water and shake well, then let it settle for 15 minutes.
3. If there is sand lining the jar, it might indicate your horse is consuming sand but passing it easily.
4. If there is no sand, either your horse is not consuming substantial amounts of sand, or he's not passing the sand he's ingesting, putting him at risk for colic.
Still confused about your horse's sand intake? Call your veterinarian. He or she can use a stethoscope to listen to your horse's gastrointestinal tract. Intestines that contain sand, despite little to no sand appearing following the "jar test," sound like waves hitting an ocean shore. The veterinarian can suggest management options for these horses, such as increasing exercise or administering psyllium or mineral oil.