Steamed hay benefits horses with airway disease by reducing respirable particles. High-temperature steaming, however, damages protein in hay and reduces its digestibility.

“While advantageous for respiratory health, steamed hay may not have ideal protein and amino acid content for some horses. Particularly for broodmares, growing horses, and performance horses,” said Catherine Whitehouse, M.S., a nutrition advisor for Kentucky Equine Research.

Steaming hay, particularly low-quality forage, reliably reduces the microorganisms (e.g., bacteria), dust, mold spores, and other respirable particles that contribute to inflammatory airway disease/equine asthma. Approximately 60% of horses are affected with mild/moderate asthma, and an additional 10-15% suffer severe asthma, giving this disease welfare and economic importance.

Previous studies support using steamed hay for reducing respirable particles but noted that various nutrients and minerals are leached from the hay during the process. A group of German researchers conducted a study to further evaluate the effect of high-temperature steaming on protein and amino acid levels.^*

The Science:

Samples of hay were collected and processed using a commercial steamer according to the manufacturer’s instructions. Average temperature during the steaming process was about 206° F (97° C). Nutrients were quantified using standard laboratory techniques, including prececal digestibility of crude protein and amino acids.

“Prececal digestibility is a measure of nutrients digested enzymatically in the small intestine. Proteins that are digested prececally are readily available to the horse and are considered high-quality protein sources,” explained Whitehouse.

Compounds called “Maillard reaction products,” indicators of heat damage to proteins, were also measured.

This study found that while crude protein levels (i.e., a measure of total nitrogen) remained stable in steamed hay, insoluble crude protein did not, resulting in increased protein that is not available prececally.

“These changes were presumed to be due to heat damage to the proteins in the hay,” Whitehouse said. Maillard reaction products were also increased, confirming heat damage.

Finally, the soluble fractions of crude protein declined, decreasing prececal protein digestibility and prececal digestibility of specific amino acids, including lysine, a limiting amino acid, and sulfur-containing amino acids.

“Amino acids are the building blocks of muscle, skin, and hooves. When diets fall short of these essential amino acids, changes in hair coat, topline, immunity, and overall health may be noticed,” Whitehouse said.

In sum, despite decreased availability of protein and amino acids, steaming remains a recommended practice because of the reduction in respirable particles.

How to Address Shortfalls:

How do horse owners address this shortfall?

“We simply need to take into consideration these losses and supplement the diet appropriately to ensure it is balanced and supplying adequate levels of amino acids. High-quality protein sources, such as soybean meal, alfalfa, and peas, can be added to boost protein levels and amino acids. These plant-based proteins are used in well-formulated horse feeds and ration balancers,” Whitehouse said.

Resources:

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Article brought to you by KER.

^*Pisch, C., M. Wensch-Dorendorf, U. Schwarzenbolz, T. Henle, J.M. Greef, and A. Zeyner 2022. Effect of hay steaming on the estimated precaecal digestibility of crude protein and selected amino acids in horses. Animals (Basel) 12(22):3092.