Digestion

Digestion in the Simple Gutted Animal
Digestion in the Young Pig
Carbohydrate Digestion in SGA’s
Young Ruminant Digestion


Digestion in the Simple Gutted Animal

In a Simple-Gutted Animal (SGA) digestion of carbohydrates begins in the mouth and continues in the bolus inside the stomach if the animal possesses salivary amylase (present in humans, some birds, the rat, but not in farm animals). If not, then carbohydrate digestion begins in the lumen of the small intestine where pancreatic a-amylase (amylopsin) begins digestion of amylose and amylopectin via dextrins, maltose and maltotriose. Maltase and iso-maltase on the intestinal brush border then complete this digestion to glucose for absorption by active transport.

Dietary simple sugars, such as glucose and fructose, do not need to be digested as they can be absorbed through the intestinal epithelium directly. Disaccharides are hydrolyzed to their constituent monosaccharides by enzymes on the brush border and the monosaccharides released are absorbed through the brush border.

Sucrose is attacked by Sucrose (Invertase) to yield Glucose and Fructose for absorption.

In young animals kept on a primarily milk-based diet (pre-weaning) or in adult humans of western European descent:

Lactose is attacked by Lactase to yield Glucose and Galactose for absorption.

Animals lose the ability to digest lactose in the small intestine after weaning. This also applies to the vast majority of humans, except those of western European descent.

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Digestion in the Young Pig

During the first few days of life, all animals can absorb whole proteins, which the adult would hydrolyze. This is particularly important in transmitting immunity from the mother to the neo-natal animal via antibodies (g-globulins) present in colostrum. This ability declines rapidly. The gastro-intestinal enzymes also have different activities which influence the diet that the young animal can consume. In the baby pig, the enzyme activities change as follows.

Birth-Five Weeks Transcript

Birth: At birth the activity of gastric pepsin, intestinal amylase and maltase are low and there is no sucrase. Lactase activity is very high. 5 Weeks: By five weeks of age the activities of pepsin, amylase, maltase, and sucrase have increased significantly. In contrast, lactase activity has decreased markedly and will eventually fall to zero. Consequently, young animals or early-weaned animals must be fed a lactose-based diet because they cannot digest other carbohydrates.

If you wean pigs at a few days, or even two weeks, you will need to include lactose in the new diet because the piglets cannot digest starch or sucrose. Older animals (after five weeks) can have these carbohydrates in their diet.

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Carbohydrate Digestion in SGA’s

[Video]

Sugar Digestion Transcript

We are currently looking at the brush border and intestinal lumen of a non-ruminant. As we zoom in on the brush border we can see the enzymes, lactase and sucrase. Glucose can enter the intestinal lumen and pass through the brush border to be used by the cell. In the young animal or in humans of western European descent, lactose from milk-based foods is digested by lactase and is broken down into its component monosaccharides, glucose and galactose, which are then absorbed through the brush border. Similarly, sucrose is digested in the small intestine by sucrase into its constituent monosaccharides, glucose and fructose, which are then absorbed. Glucose is absorbed more rapidly then fructose

Non-sugar Digestion Transcript

Pictured here is the brush border of the small intestine and the intestinal lumen. Pancreatic amylase is found within the lumen itself and maltase and isomaltase, enzymes located on the brush border, are also important in the digestion of starch. As amylose enters the intestinal lumen, pancreatic amylase breaks the alpha 1-4 linkages, releasing primarily maltose and smaller quantities of maltotriose. Both maltose and maltotriose are digested by maltase, releasing glucose for absorption. As amylopectin enters the intestinal lumen, pancreatic amylase will also act on its alpha 1-4 linkages, producing maltose and maltotriose, which are converted, to glucose. However, amylopectin also contains alpha 1-6 linkages that pancreatic amylase cannot break, resulting in the formation of limit dextrins. Isomaltase must break these alpha 1-6 linkages, again resulting in maltose and maltotriose production. The end result of starch digestion in the small intestine is the production and absorption of glucose.

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Young Ruminant Digestion

  1. The rumen and the reticulum are not fully developed and are relatively small in the young ruminant.
  2. The reticular/esophageal groove reflex, a tube-like fold of tissue, channels milk or water that is sucked from a nipple directly through the omasum to the abomasum. This is a reflex, stimulated by sucking. When the animal is weaned it normally loses this reflex but it can be maintained to some extent in the mature animal by feeding from a bottle. Calves which are bucket fed still have some reflex until weaned. Solid food, such as creep feed, passes into the small rumen and fermentation starts. The neo-natal animal has no ruminal bacterial population but from birth it starts to pick up bacteria from the mother, particularly by being licked. Any contact with mature ruminants causes inoculation. Solid food is then fermented forming acids which stimulate the growth and development of the rumen, particularly the growth of the papillae for absorption. Longer chain acids (such as butyric acid) are more effective than the shorter chain acid (acetic).

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