How horse feed changes horse behavior
As discussed in horse feed, the type of food your horse eats (grass, hay, grain, musli, etc.) affects their physical and mental wellbeing. It also has a big impact on behavior.
Mental Stimulation and Mental Illness
In a natural setting, horses spend most of their time (up to 16 hours per day) foraging for and eating grass. They derive most of their mental stimulation from the twin activities of searching for the softest and most nutritious plants, then eating and chewing them. Consequently, pasture fed horses have the maximum stimulation. Horses which are given hay to eat have much less mental stimulation in that they are not looking for food, but they still receive some from the lengthy chewing. Horses which are given energy-dense foods such as grain receive virtually no stimulation as they are not searching for the food and the food is quickly eaten as it requires little chewing.
Consequently, grain fed horses (and to a lesser extent hay fed horses) receive less stimulation and consequently tend to be less happy. If the horse spends much of its time in a box, deprived of access to pasture and contact with other horses, the overall lack of stimulation is even greater. This can result in the development of nervous behaviors and undesirable habits such as cribbing and chewing on wood, as well as repetitive movement patterns. Once such habits develop, even if the horse is then provided with a natural diet and environment, the habits tend to remain (although the severity often diminishes).
Food Quality and Activity
The quality of food greatly affects the physical activity and mental alertness of horses. We have often seen horses fed on a low quality diet looking old and tired, with little interest in what is happening around then, which gradually become active and alert when fed a high quality diet. Depending on various factors (the age of the horse, the nature of the dietary change, how long the horse was on an inferior diet) this change can happen in days or it may require weeks or months to complete.
Although the changes associated with a better diet are positive from the horse's perspective, they may not be positive from the owner's perspective. Many horse dealers feed fermented hay to their horses precisely because it depresses the horse physically and mentally, making it much more docile. Such a horse lacks energy and stands quietly in its stall most of the day. If a potential buyer comes to ride it, they will find it an easy horse to manage. However, if you buy the horse and then put it quality food, within a few weeks you may find a completely different horse. Now full of energy (especially if it is a young horse) it may no longer be content to stand in the box but may start kicking the door and walls. When you try to ride it, instead of quietly plodding along, it may try to run or even buck. Rather than meekly obeying your commands (too tired to argue) it may start to look for ways to outwit you. You may blame yourself for what you see as a negative behavioral change, thinking that it is because you do not know how to handle horses. However, the horse has just returned to its natural behavior; the horse which you purchased was essentially a drugged horse which is now no longer drugged. Furthermore, as it was previously depressed by its diet, it is likely that nobody taught it how to behave, as in its previous drugged state that was unnecessary.
Hyperactivity and Difficult Behaviors
Just as feeding a low quality food can depress a horse, food which is excessively high in easily digested carbohydrates can result in the opposite problem, that of the hyperactive horse. Just as some children become hyperactive and difficult to control when they have had too much sugar or chocolate, the hyperactive horse exhibits the same behaviors. Although not all horses are affected (just as only some children have a hyperactive reaction to sugar), with affected horses one can experience the following problems:
Such traits are most often found in horses which have high levels of grain in their diet, which quickly release large amounts of sugar into the bloodstream. Racing horses in particular are often fed mainly on grain and although their 'hot blood' temperament is usually attributed to their breeding, their feed is also responsible.
It is unknown if the hyperactive behavior is a direct result of excess sugar, or an indirect result. For example, the body releases insulin in response to excess sugar, and some scientists suggest that it is in fact the insulin which is released that is responsible for the hyperactivity rather than the sugar itself. However, from the perspective of the horse owner, the exact sequence of events is less important than the fact that by controlling the diet one can control the behavior. The expression 'feeling his oats' originates from the fact that a horse fed a quantity of oat grain will be more energetic and potentially hyperactive.
Aside from grain, certain other foods (e.g. fruits, certain vegetables such as carrots) can also be high in sugar. If your horse is getting excess sugar, one needs to reconsider the types of feed that is being used. In addition, giving a horse multiple small feeds per day rather than 1 or 2 large feeds can also help keep sugar levels even.