The GIT System
(gastrointestinal tract)
The GIT is essentially a long muscular tube running from the mouth to the anus with modified areas
along its length forming the various organs of the digestive system.
Different animals have different strategies towards digestion and their GIT systems are adapted
according to these strategies.
Different basic adaptations to the GIT
Ruminants – larger, complex stomachs and smaller intestines. Low quality, high fibre diet. These
include cows, goats, sheep and deer.
Hindgut fermenters – larger intestines for fermenting fibre. Can handle more fibre than
monogastric, but less than ruminants. These include horses, donkeys, ostriches and rabbits.
Monogastric – Single stomach compartment, comparatively simple system. Least tolerant to high-
fibre diets. These include pigs, chickens, turkeys, dogs, cats and humans.
Humans have food, animals have feed
Basics of feed
Feed is ingested as a wide variety of macromolecules which are broken down (chemically and
mechanically) into basic units which can be absorbed by the body. The absorbed molecules are
either stored or utilized by the body and then excreted as waste products.
Feed also consists of macronutrients and micronutrients.
Macronutrients are the main nutrients, required by the animal in large quantities. Micronutrients
are specific nutrients such as trace elements which are also vital to the animal, but required in very
small amounts. Very high concentrations of some micronutrients can be toxic to the animal.
Macromolecules consist of:
Dietary protein
↓
Broken down via peptidase enzymes into Amino acids
Peptidase and protease are often used interchangeably. Both refer to enzymes which break proteins down
↓
Stored as structural or secretory proteins
↓
Waste products excreted as urea
, Dietary carbohydrates
↓
Broken down via amylase enzymes into glucose
↓
Stored as glycogen in the liver and skeletal muscles
↓
Glucose is involved ATP synthesis, forming ATP energy, H2O and CO2. The CO2 is eliminated via expiration.
Expiration = Exhalation, the process of breathing out.
↓
Dietary lipids
↓
Broken down via lipase enzymes into fatty acids and monoglycerides
↓
Stored in adipose tissue
↓
Also involved in ATP synthesis, waste CO2 is expired.
Functions of GIT
Ingestion or apprehension of feed
Motility – moving feed particles via peristalsis or segmentation.
Peristalsis involves the net movement of feed particles from one point to another within the GIT.
Segmentation involves the mixing of the feed particles in one area (like a tumble drier) to facilitate
effective break down and absorption. Segmentation does not result in net movement of feed.
Along with peristalsis and segmentation, we also have oscillation and intestinal flake movement. (But these
two were not mentioned much in the coursework.)
Secretion of juices and enzymes which lubricate and break down the feed particles.
Digestion – mechanical and chemical.
o Mechanical digestion refers to grinding food smaller to increase surface area.
o Chemical digestion involves enzymes which break complex particles down into simple units.
Absorption of nutrients, electrolytes and water.
o The electrolytes such as Na, Cl, K, P, and Ca are dissolved in the water which is reabsorbed.
Egestion – excretion of waste products.
(gastrointestinal tract)
The GIT is essentially a long muscular tube running from the mouth to the anus with modified areas
along its length forming the various organs of the digestive system.
Different animals have different strategies towards digestion and their GIT systems are adapted
according to these strategies.
Different basic adaptations to the GIT
Ruminants – larger, complex stomachs and smaller intestines. Low quality, high fibre diet. These
include cows, goats, sheep and deer.
Hindgut fermenters – larger intestines for fermenting fibre. Can handle more fibre than
monogastric, but less than ruminants. These include horses, donkeys, ostriches and rabbits.
Monogastric – Single stomach compartment, comparatively simple system. Least tolerant to high-
fibre diets. These include pigs, chickens, turkeys, dogs, cats and humans.
Humans have food, animals have feed
Basics of feed
Feed is ingested as a wide variety of macromolecules which are broken down (chemically and
mechanically) into basic units which can be absorbed by the body. The absorbed molecules are
either stored or utilized by the body and then excreted as waste products.
Feed also consists of macronutrients and micronutrients.
Macronutrients are the main nutrients, required by the animal in large quantities. Micronutrients
are specific nutrients such as trace elements which are also vital to the animal, but required in very
small amounts. Very high concentrations of some micronutrients can be toxic to the animal.
Macromolecules consist of:
Dietary protein
↓
Broken down via peptidase enzymes into Amino acids
Peptidase and protease are often used interchangeably. Both refer to enzymes which break proteins down
↓
Stored as structural or secretory proteins
↓
Waste products excreted as urea
, Dietary carbohydrates
↓
Broken down via amylase enzymes into glucose
↓
Stored as glycogen in the liver and skeletal muscles
↓
Glucose is involved ATP synthesis, forming ATP energy, H2O and CO2. The CO2 is eliminated via expiration.
Expiration = Exhalation, the process of breathing out.
↓
Dietary lipids
↓
Broken down via lipase enzymes into fatty acids and monoglycerides
↓
Stored in adipose tissue
↓
Also involved in ATP synthesis, waste CO2 is expired.
Functions of GIT
Ingestion or apprehension of feed
Motility – moving feed particles via peristalsis or segmentation.
Peristalsis involves the net movement of feed particles from one point to another within the GIT.
Segmentation involves the mixing of the feed particles in one area (like a tumble drier) to facilitate
effective break down and absorption. Segmentation does not result in net movement of feed.
Along with peristalsis and segmentation, we also have oscillation and intestinal flake movement. (But these
two were not mentioned much in the coursework.)
Secretion of juices and enzymes which lubricate and break down the feed particles.
Digestion – mechanical and chemical.
o Mechanical digestion refers to grinding food smaller to increase surface area.
o Chemical digestion involves enzymes which break complex particles down into simple units.
Absorption of nutrients, electrolytes and water.
o The electrolytes such as Na, Cl, K, P, and Ca are dissolved in the water which is reabsorbed.
Egestion – excretion of waste products.
