People consider feeding straw for a variety of reasons such as reducing caloric intake, providing an alternative to horses that want to eat constantly, saving money on hay or substituting for hay when there is a shortage. Before doing it, there are some things you should know.
Straw is the dead and dried remains of oat, barley, rye or wheat plants. Straw is very deficient in protein, averaging only 5% but can be lower than 3%. It has much higher levels of all types of fiber, including the poorly digestible acid detergent fiber and virtually nondigestible lignin.
Levels of simple sugars and starch tend to be very low but straws which contain high amounts of grain in their seed heads can still be a problem for insulin resistant horses, especially since they will likely preferentially pick out this portion to eat. Calorie content is lower than hays but only by about 12% compared to mature cuttings of low sugar and starch hay.
Mineral levels are similar to those in mature cuttings of hay, but because of the higher level of fiber the minerals may not be as available to the horse. Straw is a poor source of vitamins compared to hay.
The potential for toxic levels of nitrate is higher than for hays, especially with oat straw, and levels should be checked in seasons where there was drought and in straws from irrigated fields. Fungal toxins are also more likely to be present in straws.
The very high fiber levels are what keeps the calories down in straws but this can lead to some digestive issues. “Hay belly” often develops, as can diarrhea especially in older horses.
Because straws are not that much lower in calories than hay, you can’t add straw to an existing diet and expect the horse to lose weight. If substituting it for part of the hay, it will be important to guarantee the protein, vitamin and mineral short falls are adequately met. For example, you would need to feed about a pound of a 30% protein vitamin and mineral supplement for every 6 pounds of straw to bring it up to protein levels common in good grass hays. This quickly wipes out any cost benefit for feeding straw.
All things considered, using small hole slow feeding nets to prolong eating times for your hay and adding beet pulp mixed with wheat bran at 1 lb beet pulp and 1/4 lb wheat bran (2 lbs of the mixture = 5 lbs of hay) is a better choice. Protein and minerals are at good levels, major minerals balanced. The beet pulp mixture will also soak up at least 4 times its dry weight in water, making a large and very satisfying meal.
Eleanor Kellon, VMD