Mouth cavity

The horse has strong, sensitive and highly moveable lips. Grass and other vegetation is cut using the front teeth, and the lips and the tongue are used to collect and ingest feed. Horses are highly selective grazers and can efficiently avoid unpalatable or indigestible herbage. Ingested food is ground between the large enamelled surfaces of the cheek teeth (premolars and molars). Horses chew on one side of the mouth at a time; large horses chewing 60-80 times per minute. The time spent eating varies greatly depending on the structure of the feed. Ponies usually take more time to consume their feed than larger horses. The time taken to consume 1 kg of oats or pelleted concentrate is about 10 min and 1 kg hay is usually consumed in 40-50 min. However, there is a large variation between individual horses. Table 2 gives estimates of consumption for rations with different proportions of grains and roughage. If rations are consumed too quickly, bad habits such as excessive licking, crib biting, and eating dung may develop.

Consumption time of different rations (min/kg feed) 

It is commonly recommended that horses are fed at least 0.5 kg of roughage dry matter (hay, haylage or straw) per 100 kg of body weight. Normal diets usually contain more roughage than this minimal amount. The chewing process grinds the feed between the molars in the upper and lower jaws, and reduces the particle size to about 2 mm diameter and 1-4 mm length. Young grasses are more juicy and may be swallowed before the particle size has been reduced by this much. Thorough grinding of the fibrous parts of the diet is required to ensure the passage of the digesta through the alimentary canal. Chopped roughages with a particle length shorter than 2 cm may not be chewed sufficiently, and this may cause colic.
For a horse with normal teeth there is usually no problem with chewing grains or pelleted concentrates. It is recommended that teeth are inspected and if necessary rasped twice a year to prevent protruding edges which may bruise or cut the epithelium of the cheeks (upper jaws) or the tongue (lower jaw). Young horses may periodically experience problems with chewing when milk teeth have been lost and permanent teeth are emerging. Bad teeth result in reduced consumption, chewing rates and digestion. The periods when teeth are lost or emerge are shown in Table 3.

Age at which teeth are lost or emerge in the horse:

Premolars (P) and molars (M) are the cheek teeth of the horse and are the teeth that need to be rasped. Incisors (I) are the front teeth.