All About Chaff by Dr Teresa Hollands

Oat straw- why feed it?

Dr Teresa Hollands, RNutr from the School of Veterinary Medicine, University of Surrey talks to Honeychop about their exclusively oat straw-based chaffs.

Q. What is Chaff?

Chaff or chopped straw is commonly fed to horses and ponies to bulk out their concentrate feed and to prevent them eating too quickly. Chaff is dried forage that has been cut into small pieces, in contrast to the long grass stems in hay and haylage. Traditionally a sugar blend of molasses was added to increase palatability, however you can now get lots of variations, some with oil, mint, garlic, nothing, you name it it’s out there.

Q. Should I be feeding a chaff?

You might think that chaffs are just a cheap filler for our horses and it really doesn’t matter what they are made from as we only add a handful in the bucket to slow them down and bulk up their concentrate feed. But feeding a chaff is a very useful addition to the diet, not only does it provide forage (which should be the foundation of any horse’s diet) but it also encourages chewing.

This is important because unlike humans, horses only produce salvia whilst chewing. The chewing that chaffs encourage stimulates the production of saliva which protects the upper stomach from acid in the lower stomach and thus helps to maintain gastric health. So to answer your question yes feeding a chaff is a very useful addition to the diet.

Q. Why should we be more aware of what our chaffs are made from?

Chaffs can contribute to the fibre part of our horses’ diets, but they can be made from different forages. Forage/fibre is important for the following reasons: –

Fact: Horses evolved to eat fibre. Their whole digestive system is set up to make the most of herbage…, from the shape of their jaw bones, and the arrangement of their teeth through to the large fermentation vats at the end of their digestive systems.

Fact: Forages should provide the foundation of their diet…

Fact: Not all forages are made equal

Fact: Not all fibre is forage

Q. Hum, interesting; can we talk a bit more about the fact that not all fibre is forage and remind us what fibre actually is, as it is a term that we use so often.

We tend to think of fibre as long and green or maybe preserved and therefore slightly brown, (grass, hay, straw!)  In other words the words fibre and forage have become synonymous in our minds. However, human nutritionists define fibre in a slightly different way, mainly because people cannot digest forage but we can digest some fibre!  Up to 45% of people’s fibre intake comes from whole grain cereals and there is a large body of scientific evidence that shows that whole grain cereals reduce the incidence of numerous diseases in people. So forages contain fibre but not all fibre comes from forages.

Q. What is fibre?

Fibre is defined as ‘lignin and plant polysaccharides that are not digested by mammalian enzymes’ which make up the plant cell wall. So in order for the horse to get the goodness from fibre, they need micro-organisms to ferment the fibre and break it down into substances that the horse can then absorb. If you chemically dissolve the plant’s cell wall, then you find carbohydrates eg cellulose and hemicellulose as well as lignin. Lignin is not a carbohydrate but it combines very strongly with other plant fibre carbohydrates. Even horses struggle to digest fibre that contains lots of lignin. This is because lignin in order to give more support to the plants intertwines with the cellulose and hemi-cellulose, which acts as an obstacle to the fibre being digested by the bacteria. Many people class forage as fibre however they are not the same.

Q. What is forage?

Forage is ‘the edible parts of plants, (other than the separated cereal), which is used as feed for grazing animals or which can be harvested for feeding’¹. Forage varies in nutritional value dependent upon how much fibre it contains and what type of fibre. Forage crops can contain between 30-80% fibre². Anything that isn’t fibre ie the cell content can be easily digested and immediately available in the small intestine.  Types of forage are grass (which is grazed) and preserved forage which include hay, haylage, and chaffs.  The bulk of the horse’s diet should be made up of forage.  Studies have shown that horses have evolved to graze up to 16 hours a day.  This highlights how important forage is for the horse and it is recommended that a healthy horse eats approx. 2.5% of body weight in forage.

Q. What feeds contain fibre?

All plant feed ingredients contain fibre. People are encouraged to eat whole grains (cereals) because cereals contain between 12-18% total dietary fibre, (TDF). In fact in the UK, about 40% of our fibre intake is from cereal ingredients,  20% from vegetables and 10% from fruit³. All plant foods contribute some dietary fibre to the horse’s diet and the different fibres contribute different characteristics and health benefits to the horse.

So hay, straw, grass, cereals, haylage, sugar beet all contain fibre, but they contain different amounts and types of fibre in their cell walls and therefore the horse’s bacteria digest, (ferment) them differently. These fibre sources therefore vary in calorie and nutrient content.

Q. What is Filler Fibre?

Straw is a good example of a forage which contains filler fibre, in fact you can think of it as the horse’s equivalent of human celery. You use nearly as many calories eating celery as you get from eating it and it will fill you up. Straw is similar and this is because it contains some of the fibre called lignin in its cell walls, which the bacteria in the horse’s hind gut struggle to digest. The calorific value of the straw to the horse is proportional to the amount of lignin and indigestible fibre in the straw. Wheat straw as everyone knows is very indigestible to the horse as it contains not only lignin but also silica.

Horses in light work and good doers will benefit from some filler fibre in their diets; horses in hard work would not normally be given filler fibres.

Table 1 Lignin content of different straws mean (min-max)

Adapa, P. et al., Compaction characteristics of barley, canola, oat and wheat straw, Biosystems Engineering (2009), doi:10.1016/j.biosystemseng.2009

Q. Why is wheat straw more often used when it is very indigestible to the horse?

Many manufacturers will use wheat or unspecified straw (chopped cereal straw) in their chaffs and this is due to the fact that we harvest more wheat straw compared to any other straw in the UK. In 2011, the Agriculture and Horticulture Development Board stated:-

“Of the estimated 12.2 million tonnes of straw below, more than half is from wheat. From our best estimates, about 30% of wheat straw is used for animal bedding on farm, 30% is sold off farm (mostly for bedding), and about 40% is chopped up and returned to the soil. “

Table 2: Available straw from harvest index calculation

Q. Do you know what straw is in your fibre feed?

Traditionally chaffs were made from oat straw, however many manufactures now use cheaper wheat or barley straw due to the rising cost of good quality oat straw.  Not all companies state what straw is used ie (cereal straw). You can check which straw is in your chaff by reading the label, however we have done a little research for you and summarised in the table below.

Table 3

Q. So if straw is just a filler, why do we feed chaff?

We want to feed fibre, fibre and more fibre to keep our horses diet as natural as possible; which is a good aim but not without its complications.  It is easy to forget that the ‘natural horse’ had access to only sparse grazing.

Recent research from Australia shows that wild ponies will have travelled around 10miles/day to procure their food…….  The biggest nutritional challenge today is that our horses at maintenance and in light work can eat excess calories from all forages. Plus it’s very likely that the work we do with the horses is less than that exerted by the wild ponies which are considered not to be in work!!!

In fact, the biggest problem with our leisure horses both in the summer and winter is that they tend to be ‘overfed but undernourished’ which is increasing their risk of Equine Metabolic Syndrome (EMS)

To complicate matters, it is essential that horses have enough bulk in their diets otherwise they will be at increased risk of colic,4 windsucking5, gastric ulcer6 syndrome; all of which impact on their health and welfare.

Q. How do we balance giving our horse’s enough bulk but cut back on their calories?

The secret of success is to choose low calorie forages such as oat straw and replace the higher fibre sources such as hay and grass with this alternative forage. It is very important that you balance the oat straw with additional protein and vitamins and minerals. The best way of doing this is to add a high quality balancer to some oat straw chaff.

Q. How much oat straw can I feed?

You should always try and feed a minimum of 2% but preferably 2.5% of your horse’s bodyweight as bulk, (in performance horses this will be a mix of forages and concentrates)  But be aware that different forages fed in the same quantity will give your horse different calories as summarised in table 4 below.

Table 4 The calorie content of 7.5Kg dry matter of different forages (350kg pony eating 2% bodyweight)

Q.  Does feeding straw cause colic?

An overview of the causes of colic⁷ indicates that there is a decreased risk of colic in horses fed varied diet with a high proportion of forage, but no risk was associated with the feeding of straw.

A similar study with donkeys, which are traditionally fed more straw compared to horses also showed no increased risk associated with the feeding of straw, but did with poor dental health.⁸ Interestingly, a more recent study has highlighted that horses fed haylage are at greater risk of colic compared to horses fed other forages.⁴


Q. I have been told that I shouldn’t use straw if my horse is at risk of gastric ulcers, (GUS) why is that?

Generally the most successful approach to dietary management of GUS, is to ensure that we minimise acidification of the stomach by meal management so it mimics the natural digestive physiology and function of the equine stomach.  Saliva which is the main buffering agent in the stomach is only produced when your horse chews and 1ml of saliva is produced per chew.⁹

Table 5

Oat straw chaff helps all of the above; however some people think that not all fibre provides the same protection

A study in Denmark showed that eating straw was associated with increased risk of GUS (4.5 times greater risk)¹⁰, BUT these horses didn’t have access to any other fibre, only their straw bed, which is rather misleading.

It is very likely that horses with only access to a straw bed would have lower fibre intake compared to horses with other sources of forage.  It is true that a lack of fibre has been associated with GUS and therefore the overall lack of forage is likely to have predisposed these horses to GUS (It’s probably a good thing they weren’t on shavings or the problem could have been a lot worse!!).

Actually the authors suggested that straw might irritate the stomach lining but this has not been reported in any of the other literature. They also thought that straw, doesn’t buffer the stomach acid because straw is low in calcium and protein. BUT whilst straw is lower in protein, it has a similar calcium content to some timothy hays (straw 0.1-0.3%; timothy hay 0.3-0.5%) .

You can soak hay, which reduces its calorie content (and leaches minerals!!)

Or we can think why fibre is so important in minimising the risk of GUS…

• Firstly it is due to the saliva production.
• Secondly, there is evidence that a fibrous mat, which aids buffering, sits at the bottom of the upper part of the stomach. Some people consider the fibre acts as a physical barrier preventing the acid from the lower stomach splashing up into the upper stomach. Others consider that it is the minerals in the fibre that act as a buffer when they dissociate from the fibre.

But do remember that some degree of stomach acid is needed to free ingested calcium from the fibre mat or food matrix before it can be absorbed in the small intestine. The free calcium in the stomach then acts as buffer before the food moves into the small intestine.

So it is true that fibre low in calcium (e.g. straw and perhaps most hays) might not have the buffering capacity of forage that contains more calcium.

• A simple solution if straw is being fed as a low calorie forage for good doers, is to add a balancer, which is formulated to provide the necessary protein and vitamins and minerals including calcium to your horse’s diet

Q. So what is the difference between straws used in chaffs by UK Manufacturers?

 The manufacturing team at Honeychop can help up on this one…

• Wheat straw as previously mentioned is it is very indigestible to the horse and the most harvested straw in the UK, and because of this is the cheapest straw available on the market. Traditionally it was used for animal bedding, but it is now largely incorporated into fibre feeds that are available for your horse. Not only is it the cheapest straw but it is the most in-digestible straw due to its extremely high lignin and silica content.
• Oat Straw is one of the most expensive straws to produce and it tends to be the most palatable straw. It is normally a lovely golden colour and is much softer which is all due to the fact it has a naturally lower lignin content making it more digestible
• Cereal Straw is a generic name which can be a mixture of any straws or just one.  By using the term cereal straw manufactures are able to use any straw which is readily available.  This means the horse owner will not be aware if the content of the chaff is changed.
• Nutritionally Improved Straw (NIS) is produced from cereal straw, (usually wheat). The straw is ground and milled then mixed with sodium hydroxide which helps to breakdown the fibre structure and the plant cell walls. Digestibility is enhanced and nutritional value is increased. This all sounds very good but in short Sodium hydroxide (NaOH) is most definatley not a natural product, it does dissociate in the gut and act as a buffer in ruminants so it is ok for horses; but we will let you decided on whether you want to use it or not!

So not all fibre is forage and:

         •        Oat straw contains less silica compared to wheat straw

         •        Oat straw keeps your horse chewing

         •        Oat straw is a great low calorie chaff

         •        Honeychop is free from colourings

Each of the aspects you have asked about could be an article in their own right, so please come back to our website to read more interesting articles like this.