Why steamed hay can lead to protein deficiency in horses

Hay treated with hot steam is safer for horses, but gives them less protein. Horse feed is steam treated to rid it of potentially harmful microorganisms and bind particles that might otherwise be inhaled. However, a team of scientists from the Martin Luther University Halle-Wittenberg (MLU) discovered that this also causes a chemical reaction that damages the proteins in the hay and makes it harder for horses to digest. This can lead to signs of nutrient deficiency in animals and, for example, affect growth or muscle development. The team reports on their scientific work in the journal animated.

Hot steam is used to heat the hay up to 100 degrees Celsius, which kills harmful microorganisms and binds fungal spores and dust to the hay. “Many horses suffer from lung problems such as equine asthma. The steaming process removes virtually all living microorganisms and particles from the hay that could be inhaled during feeding and damage the lungs. In theory, the end result is very good fodder,” explains Professor Annette Zeyner from the Institute of Agricultural and Nutritional Sciences at MLU.

However, her team found that the treatment also has its drawbacks, as the steam damages the proteins in the hay. “A high proportion of the proteins and the crucial amino acids contained in them can no longer be digested by the small intestine – in other words, the horse lacks these proteins as a result of the steam treatment. However, some of these protein components. they are essential for horses and cannot be absorbed in the large intestine,” says Zeyner.

The researchers demonstrated this by examining various hay samples. In the steamed hay, they found an increased number of products that are generated by the Maillard reaction, an indication that the proteins in the hay have been damaged. This is a reaction that also occurs when food is cooked, baked or fried and is responsible for browning or flavor development.

“Proteins are composed of amino acids. Steaming damages them and forms new complexes with the sugars in the hay,” says the first author of the study, Caroline Pisch, from MLU. This makes them difficult for horses to digest. According to the researchers’ analysis, the treatment almost halved the amount of protein that can be absorbed by the small intestine.

According to Zeyner, this can lead to an insufficient supply of essential amino acids from the forage protein, which is problematic for growing horses or lactating mares; young horses need protein to grow and mares need it to produce milk. To make matters worse, protein deficiency causes very non-specific symptoms in affected animals. These include impaired muscle development and a dull or dull coat with so-called “hungry hair” – isolated long hairs in the horse’s coat. Horse owners can counteract this risk by supplementing their animals’ diets with unique protein-rich forages such as yeast and soy meal or high-quality protein-rich compound forages.