AS-321 • Rev. 1977
COOPERATIVE EXTENSION SERVICE PURDUE UNIVERSITY, WEST LAFAYETTE INDIANA 47907
Digestion - the Conversion of Feed to Pork
James R. Foster, Animal Sciences Department, Purdue University
The digestive system of the pig might be compared to an assembly line in a factory. As feed (the raw materials) passes from the feed trough along this “assembly line”, it is converted into a form of nutrients that can be absorbed and later used for body functions.
Digestion includes the physical and chemical changes feed undergoes as it passes through the digestive tract. This tract includes the mouth, esophagus, stomach, small intestine and large intestine. One might consider the digestive tract as being a continuous tube with the body constructed around it.
The purpose of the digestive system is to reduce chemically-complex nutrients (carbohydrates, fats and proteins) to small units (simple sugars, fatty acids and amino acids) that can be absorbed through the intestinal wall. This reduction is accomplished by both physical and chemical processes.
What are the practical applications that can be made from a study of the digestive system? Research has shown that pigs convert feed more efficiently when the feed is ground relatively fine, as compared to a coarse grind. This can be partially explained by the fact that the more finely-ground feed offers more surface area on which the digestive enzymes can act.
The matter of enzyme digestion is also the reason why an unhealthy pig is an inefficient converter of feed. Passage of food through the pig’s digestive system normally requires 36 to 48 hours. Where disease level is high and pigs are scouring, the rate of food passage is much faster. This means the enzymes have less opportunity to break down nutrients for absorption, and much of the food passes through the tract undigested.
Following is a sequence of illustrations that traces the food as it passes through the digestive tract. The picture captions explain the changes taking place in each segment of the tract.
1. Teeth. Digestion of feed starts in the mouth with mechanical breakdown by the teeth. This chewing and grinding action of the teeth serves to increase the surface area of food particles. The increased surface area permits more efficient chemical digestion by enzymes in the mouth, stomach and small intestine. Movements by the tongue, and later the act of swallowing, also contribute to mechanical breakdown of food. The tongue acts as a plunger driving the food toward the esophagus.