It’s a fairly common question. Some people want to feed straw because they do not have access to good quality hay and want something to keep the horse busy between hay cube or pellet feedings. Others want to substitute straw for hay for overweight or metabolic syndrome horses.
Regardless of the reason for wanting to feed it, most people are under the mistaken impression that straw has virtually no food value. Whatever you think you know about straw nutritionally, the facts may surprise you.
Straw is lower in calories than hay, but not as much as you might think. On average, straw is around 14% lower in calories than hay. This is a significant drop but far from straw having no caloric value and you certainly can’t feed it free choice if calories are your concern.
The drop in calories is due to straw having higher levels of nonfermentable lignan and poorly fermentable acid detergent fiber fractions like cellulose. This has the potential to make straw pretty unpalatable to many horses. If they do eat it well, be prepared for more of a pot/hay bellied look caused by the poorly fermented fiber fractions.
Low protein is a concern with straw. It averages only about 5% protein. It needs to be combined about 50:50 with a moderate quality alfalfa hay to provide protein equivalent to good quality grass hay. Alternatively, provide 125 grams of protein from a high protein source for every 5 lbs of straw fed. This would be 312.5 grams (11 ounces) of a 40% protein supplement.
While hay is good, straw is virtually worthless as a vitamin A source. Provide 8000 IU of vitamin A for every 5 pounds of straw fed unless you are already feeding a vitamin A supplement.
Straw contains the same minerals as hay does but levels of calcium, phosphorus and magnesium are often on the low end. Trace mineral levels of copper, zinc, manganese, selenium and iodine may be similar to hay but less available for digestion if bound up by the higher fiber fractions.
Bottom line is that straw is a poor choice for reducing calories especially considering the protein, vitamin and mineral supplementation it requires. If you do feed it, combine with alfalfa or a protein supplement to avoid protein deficiency and also use a mineral supplement appropriate for your area.
Eleanor Kellon, VMD