In contrast to humans, equines only produce saliva when they chew. The more chewing motions, the more saliva is produced. When a horse eats roughage it makes more chewing motions per kilogram (kg) than when it eats concentrate. As a result the horse produces more saliva ? about 3.5 litres per kg of grass hay and 1 litre per kg of concentrate. It takes longer to chew grass hay than concentrate, however ? about 40 minutes (and 2200-2500 chewing movements) for 1 kg of grass hay and about 10 minutes (and 600 chewing movements) for 1 kg of concentrates. This means that, relatively speaking, horses do not make less chewing movements and produce only slightly less saliva per time-unit when eating concentrate rather than roughage. Hence, from a saliva and chewing perspective there is not much difference in time between roughage and concentrate. Problems occur when concentrate is fed without supplying roughage.
Gastric acid is continuously produced by part of the equine?s stomach. The saliva of equines acts as a buffer, decreasing the acidity in the stomach. In nature, where horses eat grass for the convincing majority of the time, the flow of saliva into the stomach is fairly continuous. The continuously produced gastric acid is therefore made less acidic for most of the time. In conventional stable management horses are not always provided with sufficient amounts of roughage. It would not be the first time that I see horse owners stable their horse without roughage, because roughage allegedly makes their horses go ?plump?. It are often the same owners that feed concentrates to the same horse(s), in order for the horses to still have enough energy to work. The increasing acidity in the stomach due to continuous production of gastric acid and absent compensation of saliva is one of the causes of gastric ulcers. A horse that is trained well does not get ?plump? by feeding roughage; its belly muscles will be trained and keep it looking fit.