Through the past 15 and 1/2 years we have fed some alfalfa/grass mix without much difference and we have to be careful with the calories adding up with a richer diet for this easy keeper/IR horse. I’ve tried various mixes of grasses and various levels of maturity of the grasses. When he was younger and could be on pasture for meals it was mostly controlled and as soon as these pasture meals were replaced with hay as winter set in it would flare up again. Coating the underside of his tail, running down one or both hind legs. Squirting out excessive fluid with every passage of stool and gas. Nothing we did managed it until we treated him with antihistamines for a case of hives. Surprise & Delight
As for testing our hay I have completed two horse nutrition courses that taught you how to test you hay and build a balanced diet based around your hay analysis. Nothing ever showed up in the hay tests to give us answers. And I tested our well water, nothing there either.