A study from the Swedish University of Agricultural Sciences suggests that straw is a good forage option for overweight horses and others who might benefit from reduced energy intake and the resultant lower blood insulin levels.

For two periods of 21 days, the Uppsala researchers fed six horses either a grass forage-only diet of 1.22 kilograms (about 2.5 pounds) of dry matter forage per 100 kilogram (220 pounds) of body weight per day, or a diet with 50 percent grass forage and 50 percent straw. The rations, which provided 1.43 kg dry matter roughage/100 kg body weight per day, were divided into three daily meals. The horses also received a commercial vitamin and mineral ration balancer and were allowed free access to water. Bloodwork was done on the horses after each study period to measure their metabolic responses, and gastroscopic exams were performed to look for ulcer formation.

Although it’s not commonly fed to horses in the United States, straw does provide some nutrients, says Sara Ringmark, PhD. “It contains about 6 MJ (megajoules, about 239 calories each) of metabolizable energy [the net energy remaining after fecal and urinary energy loss] per kilogram of dry matter. However, the content of digestible crude protein is close to zero. It also contains a lot of fiber, which makes it harder to digest and contributes to longer feeding times. This makes it a useful supplement to horses that desire more roughage than they are allowed to for weight management reasons.”

The blood collected from the horses revealed that in addition to satisfying hunger, the half-straw diets altered each horse’s metabolic profile in beneficial ways.

“The straw diet resulted in decreased plasma insulin levels, probably as a result of lower WCS-concentration (sugars) in this diet,” says Ringmark. “This is beneficial for horses at risk of becoming overweight and/or developing laminitis, but although the WSC content was lower on the straw diet in our study, this cannot be generalized to all wheat straw batches, as the chemical composition may vary.”

In addition, Ringmark notes that when fed the straw diet, horses also had an increased plasma concentration of fatty acids. This, she says, “implies that body fat was being utilized, which is beneficial for horses in need of a weight reduction.” Ringmark continues, “Lastly, the increase of plasma protein concentrations following feeding were lower on the straw diet, implying that eating was less voracious on this diet. This is supported by observations of longer feeding times and more feeding pauses on the straw diet.”

Also significant, she says, this study showed no association between feeding straw and the formation of gastric ulcers, a potential correlation raised in a previous field study. “The tricky thing with field studies is that it is hard to control external factors,” says Ringmark. “In our study, we used six horses that were all fed one diet with 50 percent straw and one diet without straw, acting as their own controls. The environment was controlled so that the only thing that was different between the two treatments was the diet. We also ensured good hygienic quality of all feedstuff used, including the straw, through feed analyses.” She adds that hygienic straw is harvested when the weather is dry and stored under conditions that prevent mold growth.

Ringmark acknowledges there are some challenges associated with adding straw to equine rations, particularly for horses—and people—unfamiliar with the forage. “In Scandinavia, straw has been used for horses for decades,” she says. “And as it is with low-nutrient feeds, not every horse seems to find straw very palatable and some horses may have to learn to eat it. To owners of those horses, I still recommend that straw is offered because when the other roughage is finished, the straw provides the horse with an option to fast until the next meal. This enhances the possibilities for horses to perform their natural grazing behavior and—although some of the straw is left, horses often chose to eat the most palatable parts of it—increasing their feeding times.”

Reference: “Straw as an alternative to grass forage in horses—effects on post-prandial metabolic profile energy intake, behavior and gastric ulceration,” Animals, July 2021

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