University of Illinois Extension

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Q. My neighbor recently told me that hay loses it's nutrients when it ages somewhene between 6-9 months, and that hay shouldn't be used after it's 1 year old. Is this true if the hay is still green, leafy and been barn stored?
A. Storing forages for extended periods of time may cause the fat soluble vitamins (A,D,E) content to be quite low. However, the energy, protein and mineral levels are usually maintained. Therefore, the forage is still useful, providing that it has been stored in a dry, well ventilated area, has not been subjected to excessive "heating" from bacterial activity, and does not contain mold or contamination from rodents, opossum feces, etc. If horses are being fed only forages that have been stored for prolonged periods of time, and they don't have access to either fresh pasture forages or recently harvested forages, then a grain mix fortified with fat soluble vitamins should be fed in order to supplement the hay that is deficient in these vitamins. It would be wasteful to dispose of hay that is nutritious in most categories when supplementation of vitamins makes the forage acceptable to feed.