Comparative Digestive Physiology

Meat Cut	Species	Composition	Diet	Digestion
Pork Chop	Pig	80% Protein 20% Ash	Corn (Starch)	Hydrolytic
Ribeye Steak	Steer	80% Protein 20% Ash	Grass (Cellulose)	Fermentive & Hydrolytic

Steer can eat grass and produce meat products but pig can not ® because of digestion! Type of feed is determined by type of digestion.

Gastrointestinal, GI, Digestive, Alimentary, Gut = all the same thing

Two Types of Digestion

1. Hydrolytic: All digestive enzymes secreted by animal tissue

Occurs? = stomach, intestine, pancreas (secretes enzymes)

Species? = All are dependant on this type of digestion

2. Fermentive: Enzymes are of microbial origin (primarily bacteria & protozoa)

Occurs? Rumen, Cecum – these two "organs" contain a viable microbial population. **Microbes secrete the enzymes NOT the organs.

Species? Herbivores – Cows, sheep, horses, etc.

Monogastric Digestion/Absorption

Mouth

1. Food acquisition

2. Mechanical breakdown - mastication

3. Saliva

- add moisture (lubrication)

- buffer (bicarb)

- taste

- Amylase (start starch digestion – pigs and primates only; very minute roll)

Esophagus - transportation

Stomach

1. esophageal, cardiac, fundic, and pyloric regions

2. Two secretions

- HCl – perietal cells (pH ~ 2.0; chemical reaction NOT enzymatic)

- pepsinogen – chief cells (¯ pH = pepsin (active enzyme) HCl)

3. Pyloric region regulates passage of feed (digesta)

Small Intestine (enzymes from SI and Pancreas)

1. CHO

- starch ® glucose

- fiber ® fiber

2. Fats

- triglycerides ® glycerol + fatty acids

3. Protein

True Protein ® amino acids, (some not digested)

NPN ® out (some absorbed, not good)

4. Minerals ® absorbed

5. Vitamins ® absorbed

Large Intestine = H₂O absorption (minor mineral and H₂O soluble vitamins)

Ruminant Digestion/Absorption

Mouth

1. Food acquisition – tongue primary importance

2. Mechanical breakdown – mastication (no front upper teeth) remastication

3. Saliva

- add moisture (lubrication)

- **buffer (bicarb)

Esophagus - transportation

Reticulirumen * No enzymes from animal (25-30 billion bacteria/mL and 200,000-500,000 protozoa/mL)

1. CHO

- starch ® energy for microbes – VFA byproduct

- cellulose ® energy for microbes – VFA byproduct

VFA absorbed through wall of rumen, primary source of energy for the animal (up to 100% of energy needs)

2. Fats

- triglycerides ® glycerol (® VFA)+ fatty acids

3. Protein

True Protein ® amino acids ® microbial protein, (some not digested and goes to SI – by-pass or undegradable protein)

NPN ® microbial protein

4. Vitamins ® B vitamins synthesized

Omasum - H₂O absorption

Abomasum – True stomach, HCl, pepsinogen – see monogastric notes

Small Intestine (enzymes from SI and Pancreas)

1. CHO – already digested and absorbed

2. Fats - fatty acids absorbed

3. Protein

Microbial and by-pass Protein ® amino acids

4. Minerals ® absorbed

5. Vitamins ® absorbed

Large Intestine = H₂O absorption (minor mineral and H₂O soluble vitamins)