While a lot of time is spent focussed on horses that can't eat grain in their diet, cereal grains such as oats, barley, triticale, corn, rice, rye, sorghum and wheat form a valuable component of many horse's rations. Selecting the most digestible grain based feed however can be confusing, with uncooked grains like whole, cracked and crushed grains being available as well as cooked grains like extruded, micronised, steam rolled or steam flaked and pelleted grains.

The question is, which form is best for your horse, the cooked or uncooked grains?

Why we cook grains
Grains are fed primarily as a source of energy in a horse's diet and that energy isderived mainly from the white starch found in the centre of the grain. For the horseto obtain the energy from the starch it must be digested by enzymes in the smallintestine.

But digesting the starch to extract the energy is not easy for the horse because itis "packaged" within the grain in a way that makes it difficult for the horse to getto. The reason grains are cooked is to make access to the starch a lot easier for thehorse.

Howstarch is "packaged"
Starch is simply many glucose molecules all bondedtogether and bundled up into starch granules. These starch granules are then embeddedamongst protein in a structure known as the protein matrix (Figure 1).

The starch granules, embedded in the protein, are then encased within individualendosperm cells and protected by a cell wall. Many of these cells are packed tightlywithin the grains starchy endosperm (the white bit found in the middle of a grain).And the endosperm itself is protected by the aleurone layer and finally the entirestructure is covered by the seed coat (Figure 2). Now from the plant's perspective,all of this packaging is absolutely critical for its survival and is designed toprotect the plant embryo and its stored sources of energy and protein to ensure itwill be able to grow and survive for the first few days following germination.

So, the packaging is clever and essential from theplant's perspective, however for the horse, all of this packaging is just a nuisanceand prevents the horse from being able to digest and extract the energy from thegrain. In fact, this packaging was actually specifically designed to allow a grain topass through the gastrointestinal tract of an animal undamaged so it may germinatewhen it is excreted in the manure.

How does this packaging stop starch digestion?
The packaging can be likened to a security system at a casino which prevents thethieves (or in this case the enzymes) from stealing the cash (the starch). To digestthe starch the enzymes in the horse's small intestine must first breech the seedcoat, then penetrate the aleurone layer. Following this they need to be able to maketheir way through the endosperm cell walls (these are the cells that contain thestarch), then burrow through the sometimes impenetrable vault of the protein matrixbefore finally reaching the starch granule. Then, in a cruel twist of fate, if theenzyme reaches this far, it will find that the starch is bundled so tightly into aball that the enzymes cannot digest it. So the horse is presented with a difficulthurdle—just how does it go about extracting the energy held in the starch of cerealgrains?

Enter cooked grains...
It has been recognised for many years now that to effectively digest cereal grains,horses need some help. And that help comes in the form of 'cooking'. Cooking grainsusing processes like extrusion, micronising and steam flaking breaks down thebarriers the enzymes have to face in reaching and digesting cereal grain starch.

How cooking helps
When grains are cooked using a combination of heat, moisture, pressure and some formof physical process like rolling or grinding, the entire structure of the grain isdisrupted. To start, the seed coat and aleurone layer are broken and the endospermcell walls are opened up. In addition, the structure of the protein matrix isphysically disrupted so it is no longer able to protect the starch granules. Cookingalso turns the ordered and tightly packed structure of the starch granule into anopen and vulnerable structure which can be easily attacked by enzymes in a processknown as gelatinisation. Cooking simply gives the horse's enzymes access to the grainstarch so they can go about their work of cutting up the starch into single glucosemolecules, which the horse then absorbs from the small intestine into the body, whereit is used for energy.

What about cracked grains?
Simply cracking, crushing or grinding grains is the same process as chewing and aimsonly to change the physical structure of the grain, breaking the seed coat andreducing the grains particle size to give the enzymes better access to the starchwithin the centre of the grain. While the seed coat and aleurone layer barriers areremoved, physical processing only causes minor damage to the endosperm cell walls andleaves a majority of the protein matrix and starch granule structure intact, meaningonly small improvements to starch digestion will be made. Work conducted in horsesshowed that cracking corn only improved its digestibility in the small intestine ofthe horse by 1%. So while physical processing can get an enzyme through the frontdoors of the casino, gives them access to some of the cash floating around at thetables, and maybe even gets them into the strong room, it leaves the enzymes withouta key, security code or set of explosives to get it into the vault. In short, theyaren't much better than whole grains.

Does soaking grains help?
Soaking grains simply makes them much easier to chew, so soaking will help the horseto break the seed coat and aleurone layer barriers. However soaking does nothing todisrupt the endosperm cell wall, protein matrix or starch granule structure, so, likecracking grains, soaking does not help to improve starch digestion.

What happens if cereal grains are fed without being cooked?
Starch from grains fed whole or cracked will remain largely undigested as it passesthrough the small intestine and will eventually be delivered to the hindgut. This iswhere the trouble begins. The bacteria in the hindgut do not face the same barriersas the enzymes in the small intestine, and they are able to reach and rapidly fermentthe starch contained in uncooked grains. This rapid fermentation of starch causesexcessive production of acids, which accumulate in the hindgut and lower the hindgutpH (the hindgut contents become acidic). Low pH in the horse's hindgut causes amultitude of diseases and behavioural disturbances including laminitis, colic,endotoxaemia, systemic acidosis, reduced fibre fermentation, poorappetite, woodchewing and the eating of bedding as well as deficiencies in the B-group vitamins(including biotin) and vitamin K.

What about oats?
The general consensus is that oats can be fed unprocessed. As it is a larger grain,horses are capable of chewing the grain enough to break its seed coat, removing theneed for physical processing. Studies have also found that oat starch is far easierto digest than corn or barley starch in an uncooked form. So oats can be fed wholeand uncooked. However, whether oats can be fed unprocessed needs to be decided on ahorse by horse basis. Observe your horse's manure closely when you are feeding himoats. If you observe whole oat grains in his manure, whole oats is not a suitablefeed for this horse. It is important to make sure the oats you are observing in themanure are whole and not just undigested hulls. Do this by taking them from themanure and squeezing them. If they are whole you will observe the white starch oozingfrom the centre. If you want to feed oats specifically, but your horse doesn't digestthem well, cracked, steam rolled and micronised oats can be purchased.

And the moral of the story...
Don't feed cereal grains unless they have been cooked, with the exception of oats forsome horses. If you feed whole, uncooked cereal grains, your horse will get littlebenefit from them and they have a good chance of causing disease and behaviouralproblems. Remember, the reason you feed cereal grains is to provide your horse with asource of energy. Most of this energy is held within the grains starch. If the horsecan't digest this starch, then you are better off not feeding the grain at all.

Dr. Nerida Richards (PhD) is Australia's foremost expert in Horse Nutrition. Thisarticle is courtesy of FeedXL DIYDiet Planner for Horses. If you would like be among the first to receiveFeedXL newsletters then please consider subscribing to FeedXL.

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