1. Ruminant Digestive System

2. Ruminants 2.8 billion domesticated ruminants Pregastric fermentation
Cattle, sheep, deer, elk, bison
Pregastric fermentation
Ability to chew cud at frequent intervals distinguishes true ruminant from other foregut fermenters
Kangaroo, colobine monkey are not true ruminants
Four compartment stomach
Reticulum
Rumen
Omasum
Abomasum

3. Ruminants vary in size and habitat

4. Classification of Ruminants by Feeding Preference
Classes of ruminants
Concentrate selectors
Intermediate feeders
Roughage grazers

5. Concentrate Selecting Species
Properties
Evolved early
Small rumens
Poorly developed omasums
Large livers
Limited ability to digest fiber
Classes
Fruit and forage selectors
Very selective feeders
Duikers, sunis
Tree and shrub browsers
Eat highly lignified plant tissues to extract cell solubles
Deer, giraffes, kudus

6. Intermediate Feeding Species
Properties
Seasonally adaptive
Feeding preference
Prefer browsing
Moose, goats, elands
Prefer grazing
Sheep, impalas

7. Roughage Grazing Species
Properties
Most recently evolved
Larger rumens and longer retention times
Less selective
Digests fermentable cell wall carbohydrates
Classes
Fresh grass grazers
Buffalo, cattle, gnus
Roughage grazers
Hartebeests, topis
Dry region grazers
Camels, antelope, oryxes

9. Mouth
Lips range from short, relatively immobile in nonselective grazing species to very mobile (prehensile) in selective grazing or concentrate selecting species
Chew in a lateral (grinding) motion on one side of mouth at a time
Needed to increase surface area of feed particles
Feed chewed primarily during rumination in grazing species

10. Mouth - Teeth Function: Anatomy: Reduce particle size Upper dental pad
Lower incisors
Premolars
Molars

11. Mouth - Tongue Drinking, chewing and forming boluses
Prehension of feed
Covered with rough, hook-like papillae that assist in grasping feed
Important in nonselective grazing species
Taste buds
More numerous than monogastric species
More numerous on nonselective grazing species
Believed that taste is primarily used for food avoidance by grazing species while concentrate selecting species select on the basis of smell

12. Mouth - Saliva From at least three paired glands
Submaxillary, sublingual, parotid (50% of secretions)
7 L/d sheep
150 L/d cow
Aids in mastication, swallowing, forming bolus
No digestive enzymes in the saliva of mature ruminants
Provides N, P, S and Na for rumen microoganisms
Buffering compounds to maintain rumen pH and mucin to prevent bloat

13. Esophagus Involved in rumination Different from monogastric esophagus
Striated muscle along the entire length
Provides greater strength
Allows some voluntary control
Funnel shaped
Contains three sphincters active in rumination and eructation

14. Ruminant Stomach
Anatomy:
Reticulum
Rumen
Omasum
Abomasum

15. Reticulo-rumen
Although structurally they appear as a single continuous compartment, functionally they are distinctly different

16. Reticulum Honeycomb lining Formation of food bolus
No secretions
Formation of food bolus
Regurgitation initiated here
Collects hardware (nails, wire)

17. Rumen Digestion and fermentation vat
40-50 gallons
No secretions
Contains anaerobic microbes (25-50 billion bacteria/mL fluid)
Also protozoa, fungi
Produce VFA, protein
Papillae lining
Increase surface area
Absorption of VFA
Passive diffusion

18. Omasum Laminae/manyply lining Reduces particle size
Muscular folds
No secretions
Reduces particle size
Absorption of water
~60% removed
Absorption of VFAs
~2/3 of VFAs entering or 10% of total produced
Prevents buffering of the abomasum

19. Abomasum, Small Intestine and Large Intestine
Similar in structure and function to monogastric
Differences are subtle but important
Limited ability to digest starches and sugars
Little to none presented except in exceptional circumstances (high-grain feeding)

20. Abomasum True gastric stomach - four gallons in a cow pH decreases
Three regions (cardiac, fundic, and pyloric)
Digestive secretions
Proteolytic enzymes and HCl
pH decreases
from 6 to 2.5
Denatures proteins
Kills bacteria
and pathogens
Dissolves minerals
Gastric digestion

21. Small Intestine Digesta pH Functions Duodenum 2.7 - 4 Enzymes
pH change
Flow rate regulation
Jejunum – Enzymes
Absorption
Ileum Absorption
Limited fermentation
Rate of pH increase through small intestine is slower than monogastrics
Better for peptic activity
May limit pancreatic protease and amylolytic activity

22. Pancreatic Secretions
Secretion pH is
Enzymes
Amylase
Lipase
Proteases
Trypsinogen converted to trypsin
Chymotrypsinogen converted to chymotrypsin
Procarboxypeptidase converted to carboxypeptidase
Nucleases

23. Activity of Pancreatic Enzymes
Concentration of enzymes in pancreatic juice comparable to monogastrics
Activity is lower and may be affected by:
Less juice secreted/kg BW
Low digesta pH
High rate of passage
Limited activity particularly a problem for intestinal digestion of starch escaping ruminal digestion
For ruminants fed high grain diets, less than 50% of starch reaching small intestine is digested

24. Bile Secreted with pancreatic juice in the common bile duct of sheep
Secreted in the bile duct of cattle

25. Gastrointestinal Hormones
Gastrin
Origin: stomach, abomasum
Stimulus: food in stomach
Function: stimulates HCl & pepsinogen secretion, increases stomach motility
Secretin
Origin: duodenum
Stimulus: acid
Function: stimulates pancreatic secretions; slows stomach motility and acid production

26. Gastrointestinal Hormones
Cholecystokinin (CCK)
Origin: duodenum
Stimulus: fat & protein in duodenum
Function: stimulates bile and pancreatic secretions
Also regulates appetite and feed intake
Gastric Inhibitory Protein (GIP)
Stimulus: fats and bile
Function: inhibit stomach motility and secretion of acid and enzymes

27. Large Intestine Fermentative digestion
Bacteria similar to rumen, but no protozoa
Digestion in colon may account for as much as:
27% of cellulose digestion
40% of hemicellulose digestion
10% of starch digestion
Only important in conditions that increase the amount of fermentative carbohydrate entering the large intestine
Increased rate of passage of forages
High grain diets
May account for as much as 17% of total VFA absorption
VFAs are efficiently absorbed, but primarily used as energy source for large intestinal mucosa cells

28. Large Intestine Absorption of ammonia-N Mineral absorption
May account for as much as 30 to 40% of the net transport of N into body fluid
Absorbed N may be used for:
Synthesis of nonessential amino acids
Recycling of N to the rumen
Important on low protein diets
Regulated by:
Increased by increasing N concentration of diet
Decreased by increasing the amount of carbohydrate fermented in the large intestine
Mineral absorption
Water absorption
90% of water entering the LI is absorbed