Some horses paw or are aggressive at feeding time, This is more than likely due to frustration and pain than actual behavior issues. They are anxious to “self-medicate” and they are not comfortable due to the build-up of acid or ulcers. They know as soon as they start chewing and eating it will start feeling better.
The equine stomach produces acid 24 hours a day in preparation for constant uptake and can empty in as little as 15-20 minutes. Chewing activates saliva production (saliva is an alkaline substance) which buffers gastric acid.
Under natural conditions with free-choice forage, the horse will produce about five gallons of saliva every day and eventually “recycle” much of the water content via re-absorption prior to excretion.
They may also experience stress (which can cause ulcers) due to isolation; not experiencing physical interaction with other horses. Read more about Nature is Best notions here.
Feeding with slow feeders in multiple locations enables your entire herd to eat and live together full time. Equines are herd animals; they benefit physically and psychologically from direct physical interaction. Dominant members will keep the others moving as they claim various locations. The less dominant individuals nonetheless will have alternate sources to eat from; this encourages movement and can decrease cortisol levels associated with stress from being physically separated from herd members.