Study Shows Steaming Hay Can Lead to Protein Deficiency

The researchers demonstrated this by examining various hay samples collected from central Germany. 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. (The Maillard reaction is a chemical reaction between amino acids and reducing sugars that also takes place when food is cooked, baked, or fried, and is responsible for browning or the development of flavours.) 

Proteins are composed of amino acids. The steaming damages them and they form new complexes with sugars in the hay,” explains the first author of the study, Caroline Pisch, from MLU. This makes them difficult for horses to digest. According to the researchers’ analyses, the treatment reduced the amount of protein that can be absorbed by the small intestine by almost half. The pre-caecal digestibility of the essential amino acid lysine was over 50 percent lower after steam treatment. 

According to Zeyner, this can lead to an undersupply of essential amino acids from the feed, which can be a problem for growing horses or lactating mares; young horses need proteins to grow, and mares need them to produce milk. To make matters worse, protein deficiency causes very unspecific symptoms in the affected animals. These include impaired muscle development and a dull or shaggy coat with so-called “hunger hair” — long isolated hairs in the horse’s coat.  

She suggests that horse owners can counteract this risk by enriching the animals’ diet with protein-rich single feedstuffs such as yeast and soybean meal or high-quality protein-rich compound feeds.  

The report concludes: “Steamed hay is still a proper and sometimes the only possible roughage for horses suffering from respiratory diseases such as equine asthma. Essentially, horse diets based on steamed hay should be balanced accordingly.”