The Mouth
The mouth is where the feed enters the digestive tract and where the mechanical breakdown of feed begins. Digestion in the mouth is mainly mechanical digestion, which involves chewing – helps to break up large particles to make mixing and swallowing possible.
Food is taken into the mouth by the lips, teeth and tongue. The upper lip and jaw of the pig are modified to form the snout that the pig uses to dig into the ground for food. The lower jaw acts as a “spade” for food intake.
The teeth, especially the premolar and molar teeth, chew and grind feed into smaller pieces. During chewing the jaws move up and down and from side to side. The tongue helps to push in between the teeth.
Fluid is obtained through suction. The lips are kept closed except for the part inner the surface of the water, and the tongue is used to create a vacuum in the mouth. Suckling piglets drink by creating an extensive vacuum in the mouth. The tongue with its taste buds enables the animal to distinguish between tasty and bad food and to get rid of foreign objects present in the feed in the mouth.
Before an animal can swallow dry food, it must be mixed and moistened with saliva. Saliva is alkaline with a pH of 7.3 and contains about 99 % water, the remaining 1 % consists of mucin, inorganic salts, the enzyme -amylase and the complex lysozyme. Saliva is secreted by three salivary glands (one mandibular gland and two sublingual salivary glands) in the mouth and has the following functions:
- Saliva acts to soften and moisten the small feed particles so that they can be swallowed easily.
- It lubricates the mucous membranes of the mouth and pharynx, keeping them moist.
- It has antiseptic properties.
- It serves as a solvent for food in process of tasting.
- It is important as a binding agent during the formation of a food bolus.
- Saliva also contains amylase (a carbohydrate-digesting enzyme), which starts the digestion of starch to maltose in the mouth. [Little amylase is found in horses (hindgut fermenters) and none in ruminants.]
Not much digestion occurs in the mouth since the food is quickly swallowed and passed along the oesophagus to the stomach
The act of swallowing can be roughly divided into three stages:
1. Formation of a bolus:
After the food is chewed, a bolus is formed with the aid of the tongue. The tongue also helps to push the feed bolus towards the oesophagus. This is done voluntarily and can be stopped at any time.
2. Passage of the bolus through the pharynx:
When the bolus enters the pharynx, involuntary contraction of the muscles in the pharynx forces the bolus into the oesophagus.
3. The peristaltic movement of the oesophagus:
This is initiated by food in the oesophagus. Peristalsis consists of alternative or rhythmic relaxation and contraction of the muscles in the wall of the oesophagus, forcing the bolus towards the stomach. Liquids are carried about five times as fast by a squirting action of the mouth and pharynx. Peristalsis in the opposite direction may also occur and is known as retro-peristalsis.
The mouth of a pig