Nutrition: Processed feeds, what’s the story?

NUTRITION

Processed feeds, what’s the story?

Processed is a word that some horse owners shy away from. DR CLARISSA BROWN-DOUGLAS explains why processed feeds should not be a cause for concern.

Feed proceeding methods have been researched and developed to help horses, not harm them. Even the practice of baling and preserving hay is a form of processing. So, what’s going on? While superprocessed food has a bad reputation in human nutrition, horse feeds are a far cry from our sugar-laden snacks!

Purpose of processing

The goal of processing horse feeds is to make the feed better for either the horse or owner. Processing improves digestibility, extends its shelf life, or is used to make feeds such as soybean meal and hulls, rice bran, and beet pulp.

For concentrates, processing enables the manufacturer to make consistent products. In turn, the products become safer, easier to chew, and more appetising for the horse. Processed forages such as hay cubes or pellets can make the most efficient use of limited storage space, fill in when a hay crop has failed, make it easier to carry feed when travelling, guarantee a consistent intake of nutrients, simplify ration balancing, and help horses with problems such as poor teeth or respiratory tract disorders.

Grain and forage processing

Grains are processed to increase digestibility. Crushing, cracking and grinding, particularly of corn and lupins, are performed to reduce the particle size. Other effective processing methods are crimping, flaking, and the rolling of oats and barley. These techniques open the outer coat of the grain to aid chewing. Adding heat to these processes to produce steamrolled, steam-flaked, and micronised grains improves starch digestibility.

Sun curing or quick drying hays and beet pulp reduces the moisture content of roughages so they will not mould. Chopping forages to shorten fibre length, and, although not common in Australia, ensiling or anaerobic fermentation of forage to preserve its nutrients, are all forms of processing.

Feed processing

Feed processing is least complex when grains are mixed and coated with oil and molasses to create a sweet feed. More elaborate processing changes the entire form of a mixture of feed ingredients, as with pelleting or extruding, in which ingredients are ground to improve digestion rate, and decrease segregation and mixing problems.

Pelleting

FACING PAGE: The practice of baling and preserving hay is a form of processing. ABOVE: Pelleting causes gelatinisation of grain starches, making them more available for enzymatic digestion.

balance of nutrients as sweet feeds but in a more convenient form. In the pelleting process, ingredients are ground to the same particle size, mixed with a pellet binder, and then steam heated to 82-87°C for about 20 seconds. The mash is pushed through a pellet die of the desired size, cooled, and dried to prevent mould growth. With forage pellets, the forage is dehydrated, ground, mixed with a pellet binder, and then pressed through the die.

Pelleting causes gelatinisation of grain starches, making them more available for enzymatic digestion. This is particularly beneficial for pellets made with substantial amounts of ground corn. But if the pellets looks very shiny, an indication that only partial gelatinisation has occurred, they should be avoided.

Pelleting also offers other benefits. Because the grains are ground to the same size, there is no sorting out of fine ingredients. Pellets are also convenient to handle, and don’t go rancid as readily as sweet feed in the summer.

Some horse owners question the effects of heat treatment on the viability of vitamins and minerals added to the pellet. Heat normally will not affect the minerals because they are inorganic. Vitamins are generally coated in a special gel to protect them from oxidation and are made to tolerate short bouts with heat. However, if the pelleting process is not done correctly and the pellets become too hot, availability of vitamins and possibly chelated minerals may decrease.

Fine ingredients are usually combined into a mixing pellet and then used in sweet feeds. The mixing pellet usually contains the protein sources and vitamin and mineral premix. The mix blends better if all the ingredients are about the same size. Manufacturers of sweet feeds once had a problem with fine ingredients sifting to the bottom of feed batches, so the mix may have been different in each bag. To combat this problem, molasses became commonplace in sweet feeds. Molasses, combined with the addition of mixing pellets, has resolved all problems associated with fines.

The trick to recognizing a good quality pellet is to look for relatively long, hard pellets (except for pellets used in special senior concentrates) with good colour, uniformity, a dull surface, and few to no fines. When a pellet can be handled repeatedly without falling apart, it is considered durable, an important consideration when evaluating pellets.

Extruding

Extruded nuggets are made from many of the same ingredients as pelleted feeds. The grains are ground and mixed with all other ingredients, and then cooked with moist heat at about 127°C. Even more complete gelatinisation of starches occurs during extrusion than during pelleting. The extrusion occurs when the mash is exposed to cooler air, and it begins to expand and pop, much like pop-corn. The nuggets are dried to a moisture level of about 10 per cent before being bagged.

Many of the advantages of pelleting also hold true for extruded feeds. One additional advantage is the ability to add high levels of fat. With oil in the mash and oil sprayed on the outside of the nugget, fat levels can be as high as 20 per cent. Because of high temperatures during processing, preservatives are not always necessary (except with high fat nuggets), another benefit. The heat does affect vitamin levels, but because vitamin degradation is expected, manufacturers put in extra vitamins to compensate for losses. Energetically, extruded feeds have the edge in digestibility over conventional grain, sweet feeds, and pelleted feeds. The form also slows feed intake, which is advantageous if the horse eats its feed too quickly. However, it is difficult to get a horse in need of a large quantity of feed to eat enough of an extruded ration. Extruded feeds are very low in fines and

Processed forages such as hay cubes or pellets guarantee a consistent intake of nutrients.

dust, which makes them ideal for horses with respiratory problems.

There is a downside to extruded feeds. They are more expensive to manufacture and are bulkier than other feeds, and therefore require more storage space. Palatability can be an issue because of the unfamiliar form.

Processed Grains

Oats: Traditionally, oats are the feed of choice for horses because of their palatability and margin of safety, thanks mainly to their high fibre content. Even with as little processing as cleaning the beards off, they are still a very digestible source of energy for the horse.

Additional processes such as crimping, steaming, cooking, or rolling do not increase digestibility enough to make it worth the extra processing cost. The major energy source in oats is starch, which is easily attacked by the enzyme amylase so it can be digested in the small intestine, where it’s energetically of most benefit to the horse.

The problem with processing oats is that once the integrity of the grain’s outer wall is broken, the inside is exposed to air, which begins oxidation and the eventual breakdown of nutrients. If the grain is steam or heat treated, its nutritional value lasts longer, because the enzymes in the grain that cause deterioration will be denatured by the heat.

The limiting factor to oat digestibility is the horse’s ability to chew oat grains. If whole grains are showing up in the manure (not just the hull), then it is time to evaluate the horse’s teeth. Aged horses who are losing teeth would benefit from processed oats.

Corn and Barley: Contrary to oats, processing corn and barley is beneficial. Both are higher in starch than oats, but in order for the horse to get the most out of this starch, it needs to be heat processed. With their large crystalline structure, corn and barley starch molecules are not easily broken down by the amylase enzyme. However, heating makes the molecules more vulnerable to amylase and subsequent digestion. In a recent study, different forms of corn were compared by looking at their glycemic index, a measure of small intestinal digestibility. When horses were fed cracked or ground corn, there was little difference in glycemic index, but when steam-flaked corn was fed, the glycemic indexes were significantly higher. The steam treatment made the corn molecules much easier to digest. Many horse owners boil barley to feed their horses, another method to gelatinise the starch and improve digestibility.

Digestibility is important because when grain escapes digestion in the small intestine and passes through to the large intestine, the microbial population ferments the starch. The by-product of starch fermentation is lactic acid, which lowers the pH of the large intestine, making it more acidic. The more acidic the environment, the unhealthier it is for the fibre-digesting microbial population, which can lead to issues with hind gut acidosis including colic, poor performance, and laminitis. Keeping the microbial population in balance with a desirable pH is essential to the health of the horse.

In summary, horse owners should not necessarily shy away from processed feeds. Feed processing can improve digestibility and palatability of grains and other ingredients, and provides a convenience to the horse owner. That said, incorrect processing and the use of poor quality ingredients will result in poor feed. So always look for a reputable manufacturer that specialises in quality equine feeds made according to the latest in equine nutrition knowledge.

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