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Since grain has fallen into disrepute as a concentrated feed, more and more feeds have been brought onto the market that contain or consist largely exclusively of structured chaff. These can be identified in the feed by their green stems, typically measuring 1-4 cm in length. This is usually chopped hay or lucerne stems.

In terms of nutritional value, these structured chaffs are more comparable to hay than to concentrated feed—even when placed in the trough.

According to the manufacturers, these are designed to encourage the natural chewing and digestive activity of horses while facilitating ‘healthy’ and ‘low-calorie’ trough feeding—because what do horse owners love more than filling their darling’s feeding trough? Even if the horse should, in fact, not be fed anything at all due to a lack of training or its light feeding behavior.

Are structured chaffs really safe?

Nevertheless, there is some evidence suggesting that the incorporation of structured chaff in horse feed may pose potential challenges to the digestion and health of the animals.
Some studies have explored the impact of feed fiber length on the chewing behavior of horses.
We now understand that horses require a minimum fiber length of 8 cm to properly chew plant fibers.
This chewing process subsequently produces fiber lengths ranging from 1.6 to 5 mm, which are swallowed and contribute to optimal digestion.

Short fibers between 1-7 cm pose significant problems as they cannot be adequately chewed. These fibers are swallowed in excessively long lengths, which is also observable in the animals’ feces, as they are poorly digested and excreted. As they travel through the digestive tract, they create various complications.

In the USA, particularly, there is now intensive research being conducted on the microbiome of the horse’s large intestine. Studies have shown that any disruption in peristaltic movement can also result in dysbiosis, i.e., faulty fermentation processes. Dysbiosis has adverse effects not only on the health of the large intestine but can often lead to inflammation of the intestinal mucosa and subsequently result in leaky gut syndrome and fecal water syndrome. Given that peristalsis, particularly controlled by the length of fibers, such long structural chaffs, under normal circumstances, never reach the large intestine, they must be regarded as extremely problematic for the large intestine fermentation process.
Preliminary in vitro studies indicate that structural chaff can induce distinct fermentation patterns in the large intestine, thereby promoting the development of dysbiosis.

Dysbiosis and other health problems

It should be widely acknowledged that the health of the large intestine microbiome is pivotal for a horse’s overall health. When dysbiosis occurs, involving the colonization of pathogenic or ‘wrong’ microorganisms, it often has far-reaching effects on the horse’s metabolism and health. Interestingly, the symptoms may not manifest in the intestine but in other areas. The consequences of dysbiosis range from conditions like laminitis and chronic respiratory problems to sweet itch, underscoring the importance of not taking it lightly.

In addition to the ‘overfilling’ of the large intestine with roughage, which is no longer transported forward and excreted quickly enough, bloat can also occur. Many horses with round bellies exhibit reduced peristalsis or suffer from flatulence, contributing to the enlargement of the belly. They are frequently mislabeled as ‘fat’ and subjected to radical diets, which can result in additional health problems such as stomach ulcers and induce considerable stress.
Furthermore, impaired intestinal motility contributes to dysbiosis, exerting a negative impact on the metabolism and, consequently, the overall health of the horse. In such horses, the development of a detoxification disorder in the form of cryptopyrroluria (KPU) is nearly pre-programmed.

And the stomachs of these horses are also impacted by structural chaff. For instance, many horses with stomach ulcers exhibit faecal water syndrome in response to the feeding of structured chaff. Omitting the chaff results in a calming effect on the intestines. Apparently, the coarse stems can irritate the inflamed stomach lining, triggering a stress reaction in affected horses and subsequently leading to faecal water syndrome.
Naturally, addressing the treatment of stomach ulcers in such horses is essential. However, the pronounced irritant effect is likely not entirely without consequences, even in horses with largely intact stomach lining, when they consume coarse stems in the trough day after day.

Structured chaff can have a variety of negative effects on horse health
©️ Adobe Stock / anakondasp


In summary, it can be stated that the problematic nature of feeding structured chaff to horses is not a new revelation. Alongside a healthy dental structure, horses require long-fiber roughage such as hay, allowing them to chew and salivate properly for optimal digestion. However, small chopped hay in the form of structured chaff, commonly found in ‘leisure horse mueslis,’ can contribute to the development of digestive disorders and metabolic diseases. These issues may manifest symptomatically not only in digestive behavior, such as flatulence and faecal water syndrome, but also in other areas, serving as secondary symptoms of a KPU.

If horses require concentrated feed due to their heavy workload, it is advisable to use protein-containing feed such as sainfoin or lucerne pellets. Alternatively, in consultation with a nutritionist, classic grains such as crushed barley or oats may be considered.


Finely chopped hay in the feed trough is not only pointless but can also adversely affect the horse’s health.


David Frape, Equine Nutrition and Feeding, Blackwell Publishing, 2009, ISBN 978-1-4051-0598-9

Geor, Harris, Coenen, Equine Applied and Clinical Nutrition, Saunders Elsevier, 2013, ISBN 978-0-7020-3422-0

Drogoul, C., Poncet, C., & Tisserand, J. L. (2000). Feeding ground and pelleted hay rather than chopped hay to ponies: 1. Consequences for in vivo digestibility and rate of passage of digesta. Animal Feed Science and Technology, 87(1-2), 117-130.

Miyaji, M., Ueda, K., Hata, H., & Kondo, S. (2011). Effects of quality and physical form of hay on mean retention time of digesta and total tract digestibility in horses. Animal feed science and technology, 165(1-2), 61-67.

Silva, Vinicius Pimentel, et al. Passage kinetics of digesta in horses fed with coastcross hay ground to different degrees. Ciência e Agrotecnologia, 2014, 38. Jg., S. 506-514.

Van Weyenberg, S., Sales, J., & Janssens, G. P. J. (2006). Passage rate of digesta through the equine gastrointestinal tract: A review. Livestock science, 99(1), 3-12.

Hill, J. (2007). Impacts of nutritional technology on feeds offered to horses: A review of effects of processing on voluntary intake, digesta characteristics and feed utilisation. Animal Feed Science and Technology, 138(2), 92-117.

Murray, J. A. M., Bice, R. K., & Moore-Colyer, M. J. (2010). The effect of particle size on the in vitro fermentation of different ratios of high-temperature dried lucerne and sugar beet pulp incubated with equine faecal inocula. Animal feed science and technology, 162(1-2), 47-57.

Hume, I. D., & Sakaguchi, E. (1991). Patterns of digesta flow and digestion in foregut and hindgut fermenters. In Physiological aspects of digestion and metabolism in ruminants (pp. 427-451). Academic Press.

Clauss, M., Steuer, P., Erlinghagen-Lückerath, K., Kaandorp, J., Fritz, J., Südekum, K. H., & Hummel, J. (2015). Faecal particle size: digestive physiology meets herbivore diversity. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 179, 182-191.

Vervuert, I., Bochnia, M., Coenen, M., Brüssow, N., Hollands, T., & Cuddeford, D. (2010). Electromyographic evaluation of masseter muscle activity in horses fed different types of roughage. EAAP Scientific Series, 128(1), 75-77.

Petz, V., Khiaosa‐ard, R., Iben, C., & Zebeli, Q. (2023). Changes in eating time, chewing activity and dust concentration in horses fed either alfalfa cubes or long‐stem hay. Veterinary Medicine and Science.

Taylor, L. A., Müller, D. W., Schwitzer, C., Kaiser, T. M., Castell, J. C., Clauss, M., & Schulz‐Kornas, E. (2016). Comparative analyses of tooth wear in free‐ranging and captive wild equids. Equine Veterinary Journal, 48(2), 240-245.