Digestive Systems

1. Digestive Systems Chris Ellason

2. Digestion and Absorption: • The process of digestion includes: • The prehension of food or feed • The mechanical chewing and grinding • Mixing with digestive acids and enzymes to chemically break down feedstuffs • The process of absorption includes: • Transport of the digested foods across the intestinal mucosa to the blood or lymph system

3. General Terms • Prehension: to take into the mouth • Mastication: chewing • Deglutition: swallowing • Regurgitation: the backward flow of food through the esophagus

4. Three Major Categories • Carnivore: consume flesh of other animals, examples are dogs and cats • Omnivore: consume both plants and flesh, examples are primates • Herbivore: consume plant material, examples are horses and cattle

5. Carnivore • Very Well developed stomach • Uncomplicated intestine • Limited fiber digestion

6. Omnivore • Combination of carnivores/herbivores • More complicated GIT than carnivores • Colonic digesters • Pigs, humans • Cecal digesters • rat

7. Herbivore • Cow, horse, rabbit • Each has a different type of GIT • Cow- ruminant • Horse- simple stomach, large cecum, large sacculated LI • Rabbit- larger stomach, very large sacculated cecum, unsacculated LI

8. Salivary Glands • 3 pair • Parotid • Mandibular • Sublingual • Water - moistens food aids in swallowing • Mucin - lubrication for swallowing • Bicarbonate salts • Enzymes

9. Salivary Glands

10. Salivary glands

11. Different Digestive Tracts • Farm animals have a variety of digestive systems • Ruminants: have 4 different compartments to the stomach • Examples include cattle, sheep, goats • Nonruminants (also known as monogastrics) • Hogs, dogs, and cats have a single, simple stomach • Poultry have a two part stomach • Horses have a large, functional cecum

12. Pregastric vs Postgastric • Pregastric: Fermentation that occurs in the rumen of ruminant animals. It occurs before food passes into the portion of the digestive tract in which digestion actually occurs. • Postgastric: The fermentation of feed occurs in the cecum, behind the area where digestion has occurred.

13. Pregastric vs Postgastric • Ruminants • More efficient • Less intake • Non- ruminant herbivores • Only postgastric • Less efficient • Greater intake

14. Monogastric Systems • Mouth: prehension and chewing of food; some carbohydrate enzyme activity • Esophagus • Stomach • Storage • Muscular movements (break down food) • Secretes Digestive Juices (hydrochloric acid) • pH about 2

15. Monogastric Systems

16. Small Intestine • Duodenum • Active Digestion Site • Produce enzymes • Pancreas • Helps to neutralize ingesta entering the SI • Liver • Produces bile; breaks down fats • Intestinal Walls

17. Small Intestine • Jejunum • Active in nutrient absorption • Ileum • Active in nutrient absorption • Villi • pH 6 to 7

18. Large Intestine • 3 Sections • cecum • colon • rectum • Active in water resorption • Secretion of some minerals • *Bacterial Fermentation*

19. Horses are Different • Saliva • contains no enzymes • may secrete up to 10 gallons/day • stimulated by scratching • Esophagus • only one way peristaltic movement • Impossible for regurgitation

20. Horses are Different • Stomach • much smaller in comparison to other species • not very extensive muscular contraction • So how should we feed differently? • Small Intestine • same as pig but no gall bladder • Can’t handle a high fat diet

21. Horses are Different • Large Intestine • over 60% of GIT • 4 parts • cecum • large colon • small colon • rectum

22. Cecum and Large Colon • Similar to Rumen • bacterial cellulose breakdown • bacterial protein breakdown • VFA production • Water Soluble Vitamin production

23. Small Colon and Rectum • Primary site for water resorption • Can become impacted with feed

24. Horse GI Tract

25. Avian Species • Beak • no teeth • can be used to reduce particle size • Esophagus • ingesta holding and moistening • Salivary Amylase • Fermentation in some species

26. Avian Species • Proventriculus • Gastric juice production • pH 4 • Rapid pass through of food

27. Avian Species • Gizzard (ventriculus) • thick muscular wall • particle size reduction (similar to mastication) • nonglandular • normally contains grit • no enzymatic secretion

28. Avian Small Intestine • Functions in digestion and absorption of feed and nutrients just as in other monogastrics • pH is slightly acidic • Most enzymes found in mammals except?

29. Avian Large Intestine • Contains 2 blind pouches instead of ? • Mostly water absorption • Some bacterial activity but less than in most mammals • very short in comparison

30. Avian Species

31. Ruminant Digestive System • Mouth • what is unique about the teeth? • Can only chew on one side of mouth at a time • Saliva production is continuous • Production about 12 gallons/d

32. Rumen Stomach • 4 PARTS • reticulum • rumen • omasum • abomasum

33. Reticulum • Honeycomb • most cranial • not truly separated from rumen • no enzymatic secretion • walls are tough, tend to catch heavy objects

34. Rumen • Large compartment extends from diaphragm to pelvis • papillae • Fermentation chamber • Majority of absorption of byproducts and conversion to volatile fatty acids

35. Rumen Digestion • Reticulorumen provides a favorable environment for bacterial fermentation • Continuous turnover of digesta and removal of fermented digesta • Anaerobic fermentation

36. Omasum • Manyplies (Stockmans Bible) • short blunt papillae • very muscular • no enzymatic secretion • reduction of particle size • water resorption

37. Abomasum • True Stomach • First Glandular portion of the tract • Very similar in structure and function to nonruminant stomach

38. Other Unique Points • Esophageal Groove • cardia to omasum • milk bypass • Rumination: The process where rumen contents are regurgitated, remasticated, and reswallowed for further digestion • Eructation: expulsion of accumulated fermentation gases from rumen via esophagus

39. Ruminant GI Tract

41. Rumination • Regurgitation of ingesta with mastication • reticular contraction that concentrates ingesta at the cardia • increased inhalation of air at same time • contraction of diaphragm • ballooning of esophageal walls • ingesta sucked into esophagus • returned to mouth by reverse peristalsis

42. Rumination • Excess liquids are swallowed • Mastication commences • More time spent masticating here than initial intake • Amount of time ruminating is a function of diet composition

44. Rumen Contents and Motility • Rumen contents are not uniform • Occur in stratified layers • Change from ventral to dorsal • Rumen mat • high concentrate diets eliminate mat • more viscous fluid in high grain diets • lowest dry matter in high forage diets

45. Rumen Contents and Motility • Motility of rumen mixes contents • Divided into • primary contractions • secondary contractions • Contractions require up to 50 seconds to complete

46. Rumen Contents and Motility • Contractions begin with reticulum • Progress dorsally • Finish with ventral blind sac and ventral pillars

47. Rumen and Acute Acidosis • Optimal rumen pH is 6.7 • Variation in pH is normally +/- 0.5 • Introduction of high grains result in • breakdown of rumen mat • proliferation of facultative anaerobes • these produce high levels of lactic acid

48. Rumen and Acute Acidosis • Lactate is a much stronger acid that other VFAs • In severe cases lactate can make-up well over 50% of total rumen acids • Succinate and Formate can also appear in high quantities

49. Rumen and Acute Acidosis • Increased acids can reduce pH as far as 4.0 • Severe rumenitis occurs at these pH levels • Absorption of lactic acid results in systemic acidosis • All chronic acidosis results in rumen parakeratosis

50. Factors Affecting Digestibility • Rate of passage: increased rate of passage of digesta through the tract reduces digestibility • Factors increasing rate of passage include: • Increased level of feeding/intake (ruminants) • Finer processing (such as grinding) of feed Note: grinding grain usually increases digestibility but grinding hay decreases digestibility