Straw is often recommended as an alternative to hay in a variety of scenarios: hay shortage, for weight loss, to decrease sugar/starch in the diet, or simply to give the horse something to chew on for longer periods, without increasing calorie intake. Straw is an especially common recommendation for feeding donkeys.
Hay, grain, and an apple - staples in a horse's diet
Feeding straw results in a small reduction in calories but a much higher loss of protein, vitamins, and fermentability compared to feeding hay.
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Straw is the dead stalks of grain plants, cut after the grain has been harvested. The plants are allowed to die and dry out before harvesting, to reduce moisture in the grain. In some areas the plants are sprayed with glyphosate to hasten their death and drying. This is a very different scenario from harvesting hay which is done when the grasses are still alive and green at a nutritional peak.
The major reason most people feed straw rather than hay is to reduce the calories, but there really is not that much difference – 0.789 Mcal/lb on average versus 0.913 Mcal/lb for grass hay which is a 14% drop. (Dairy One Feed Composition Database). If you are already feeding a mature hay, or one chosen for low-sugar and starch levels, the difference is even less, since they typically run about 0.850 Mcal/lb with straw then offering only a 7% reduction in calories.
Straw isn’t necessarily safe from a sugar and starch standpoint either. Sugar as high as 6.2% has been reported and starch up to 4.3%. Straws with a large amount of grain left in the seed heads will be even higher.
There are significant differences in the fiber fractions and not in a good way. ADF and NDF are very high, making straw more difficult to ferment which may result in “hay belly”, and diarrhea, or free fecal water in older horses especially.
Protein is also severely deficient, averaging 5.3% in straw versus 10.9% in hay, necessitating protein supplementation. Mineral levels are similar, except for lower average phosphorus and magnesium, but may be less available because of binding to the higher fiber fractions.
Straws have virtually no vitamin value. Because they are difficult to ferment, they are poor support for the microorganisms which would normally produce B vitamins for the horse. To top it off, there is a higher risk of toxic nitrate levels in straw https://hereford.org/wp-content/uploads/2017/02/issue-archive/0217_Nitrates.pdf .
In summary, there is a small reduction in calories but a much higher loss of protein, vitamins, and fermentability compared to feeding hay. With all the supplementing you will have to do, including for donkeys, you won’t save any money and analyzing for nitrates is advisable. You are better off investing in slow feeder nets and feeding a nutritionally appropriate hay.
About ECIR Group Inc.
Started in 1999, the ECIR Group is the largest field-trial database for PPID and EMS in the world and provides the latest research, diagnosis, and treatment information, in addition to dietary recommendations for horses with these conditions. Even universities do not and cannot compile and follow long term as many in-depth case histories of PPID/EMS horses as the ECIR Group.
In 2013 the Equine Cushing's and Insulin Resistance Group Inc., an Arizona nonprofit corporation, was approved as a 501(c)3 public charity. Tax deductible contributions and grants support ongoing research, education, and awareness of Equine Cushing's Disease/PPID and EMS.
THE MISSION of the ECIR Group Inc. is to improve the welfare of equines with metabolic disorders via a unique interface between basic research and real-life clinical experience. Prevention of laminitis is the ultimate goal. The ECIR Group serves the scientific community, practicing clinicians, and owners by focusing on investigations most likely to quickly, immediately, and significantly benefit the welfare of the horse.
Press release by Eleanor M. Kellon, VMD