Question:  I have an 18 year old gelding that was diagnosed with irritable bowel syndrome. Ultrasound showed enlarged lymph nodes in the small intestine. We took the horse off grain (fed 1st cutting grass/alfalfa hay, pasture, and Alfa-lox) and the horse got better. Now 18 months later on the no grain diet he did well on before, he dropped weight, was lethargic, and only interested in eating hay again. The only difference is that he didn't colic this time. Blood tests, scoping, UT, liver enzymes etc showed no problem. Any suggestions for feed that may help this horse? My vet seems to be out of options and we aren't even sure it is food related. Thank you. Dr. Kellon: Your history is most consistent with malabsorption: 
You could discuss with your vet doing a glucose absorption test.  If you use Karo syrup at 0.15 mL/kg the peak glucose occurs at about 60 minutes so not unreasonably long for a test at home.  Fast overnight and day of test, pull blood at 0 and 60 minutes for glucose.
If this is a small intestinal malabsorption, he will do better for maintaining weight on a fermentable diet - which already seems to be the case here.  Beet pulp with copra could be a very good dietary addition, as would the Absorb All.  Addition of the three most critical amino acids by feeding Tri-Amino will optimize efficiency of utilizing protein and help with muscle loss.