by Dr Derek Cuddeford, Royal (Dick) School of Veterinary Studies, University of Edinburgh
The basic feed of horses is forage and what is in it depends on its age. For example young spring grass is mostly water (~85%) and the bulk of the remainder is soluble carbohydrate and protein with little indigestible fibre so it has a high feed value. As the plant material ages the protein and water content decline whereas the indigestible fibre (lignified cell wall material) increases; there is a reciprocal relationship between protein and lignified fibre. Whether it is grass in the field or hay or silage, the age of the crop materially affects the feed value of the forage. Forage high in lignified fibre will have a low energy value as well as low nutrient status. Soluble carbohydrate levels fluctuate enormously as they depend on ultraviolet radiation from the sun. High levels of sunshine mean that grass in the field will have high levels of soluble carbohydrate in the afternoon. This is why grass is often cut after noon when making silage/haylage to ensure plenty of substrate for an effective fermentation and thus good preservation of the grass. Laminitis-prone animals will be more at risk when grazing in the afternoon although forage conserved as silages/haylages at this time should be safe to feed provided there has been an effective fermentation that “uses up” all the soluble carbohydrate.
Horses that have energy requirements in excess of maintenance may obtain enough energy and nutrients from quality forage but even this will be inadequate for lactating early foaling Thoroughbred mares, racehorses, etc. These animals with high requirements must receive a combination of forage and concentrate. The concentrate portion can be straight cereal as in the traditional way of feeding horses but this is rarely done nowadays. However some owners still like to feed some straight cereal but usually in combination with a balancer. This is to avoid any shortages of protein, minerals and vitamins that are likely to arise when just cereal and forage are fed. Thus, the majority of horses are fed a combination of forage and manufactured feed, the exact proportions dependent on the animal’s needs.
In terms of manufactured feed, what is in your horse’s feed is basically the same that is in your feed but, you get lots of other goodies in the form of E numbers! Human food manufacturers respond to the needs of the consumer who generally, is much less willing nowadays to rely on fresh food but rather to consume heavily processed food. The latter is convenient, made appetizing, stores well for long periods, requires minimum preparation, is often relatively cheap and marketed vigorously and often the subject of BOGOF (Buy One and Get One Free!). To achieve a lot of these goals involves the use of feed additives. For example sodium nitrate (or sodium nitrite) is used as a preservative, a colouring and flavouring in bacon, ham, hot dogs, lunch meats, corned beef, etc. Artificial sweeteners such as aspartame (E951) or high fructose corn syrup are commonly found in diet or sugar-free drinks, sugar-free gum, drink mixes, etc. Monosodium Glutamate (E621)) is used as a flavour enhancer in soups, salad dressings, chips, etc whilst Butylated Hydroxyanisole and Butylated Hydroxytoluene (E320) are preservatives that are found in cereals, chewing gum, potato chips, and vegetable oils. Another often used preservative is Sodium Sulfite (E221) that is used in wine-making amongst other things whereas Sulfur Dioxide (E220) is found in beer, soft drinks, dried fruit, juices, cordials, wine, vinegar, and potato products. Hydrogenated fats/trans fats are used to enhance and extend the shelf life of food products but have received a lot of bad publicity recently since they have been shown to increase Low Density Lipoprotein (LDL cholesterol is bad as it leads to atherosclerosis) and reduce High Density Lipoprotein (HDL cholesterol is good as it reduces risk of heart disease). Artificial food colourings such as Blue1/ Blue2 (E133), Red 40 (E124), Yellow 6 (E110) and Yellow Tartrazine (E102) are in common use. The latter is well known for causing hyperactivity in children and some of the other additives have been linked to much more serious conditions. It seems to me that horse feed generally is healthier than a lot of human food and does not contain a plethora of potentially harmful additives!
Another major difference between human and horse food is that the latter contains no animal materials. Thus, the raw materials that go into horse food are vegetable protein sources such as sunflower and soya meals together with cereals such as maize, barley and wheat. You can check which raw materials are included in your horse’s feed by looking at the bag label. The traditional cereal oats are rarely incorporated into compound feeds because of their scarcity and cost and are more likely to be imported (from say Finland or Canada) and fed straight, particularly to racehorses. Cereal by-products that arise from the baking, milling, brewing and distilling industries are valuable inclusions in horse diets providing in some cases additional protein, fibre or vitamins. Vegetable oils such as those derived from soya beans, linseed or rapeseed are often incorporated to provide additional energy and essential fatty acids. Vitamin and mineral pre-mixes are used to ensure an appropriate supply of micronutrients. The European Union regards yeasts and amino acids as additives which are often used to improve the quality of the diet but do not compare with the type and number of additives that are used in the human feed industry. Furthermore, it is worth remembering that amino acids are essential nutrients. Industrially-produced propionic acid, a naturally occurring end product of fermentation that is formed in the rumen of a cow and the large intestine of the horse, is sometimes used as a preservative in horse diets to extend their shelf life. Propionic acid like the other volatile fatty acids acetic and butyric acids that are also produced in the large intestine, are important energy substrates for horses. Compound feeds combine raw materials in such a way as to provide a “ready meal” that is balanced with respect to protein, fats, minerals and vitamins and targeted to meet the needs of particular horse types (mares, foals, racehorses, eventers, etc). The balance of any diet is made up of carbohydrates that contribute both fermentable and non-fermentable fibre together with highly digestible carbohydrates such as starch. Usually, cereals are cooked either by micronising or steam-flaking to improve their availability to the horse. The energy needs of the horse will govern the size of the “ready meal” and how many are fed per day. Although the energy density of compound feeds varies, say from between 9.5 to 13.5 MJ digestible energy, the majority of horses satisfy most of their caloric need by eating more or less of a compound feed. Obviously, those with the greatest need will be fed the most energy-dense diet.
The format of horse feeds vary and this can have an impact on what is in the feed. For example, many people prefer to purchase coarse mixes because they can see, more or less, the actual raw materials that have been used although the mix will usually contain at least one pellet which will be the vehicle for the vitamins and minerals which would otherwise “fall out” of the feed mix. Coarse mixes are highly palatable but may be prone to forming some dust as a result of handling and thus, some molasses or wheat syrup may be used to stick any stray particles together. In the US these mixes are often heavily molassed and are known as “sweet feeds”.
In conclusion, you might reflect on what you are eating sometimes. Many human breakfast materials resemble coarse mixes (muesli) and others, compounds such as some of the well-known cereals presented as flakes, biscuits or extrusions. Other horse foods that you eat are best exemplified by carrots and of course, human forages are represented by salad leaves, cabbages, etc. Unfortunately, sugar is added to so many foods nowadays. For example, a “healthy” cereal bar may contain the equivalent of 3.5 sugar cubes whereas a healthy adult cereal serving might only supply the equivalent of one sugar cube. Contrast that with the 9.5 sugar cube equivalents in one can of a well-known drink. The horse or pony faces a laminitis risk from the intake of forage soluble carbohydrate whereas you face the risk of Type-2 Diabetes from the excessive intake of sugar contained in fizzy drinks and processed food!