1. The Equine Digestive System
IMS #8895-A

2. Objectives Discuss internal organs
Identify the structures of the digestive system
Recognize functions of the organs comprising the digestive system

3. Digestive System Monogastric - having one stomach
Herbivores - plant-eating animals
Digestive system anatomically developed to continually digest small amount of food

4. Digestive System
Eat simple-looking feeds containing complex chemical substances
dramatic changes during digestive process before feed is used as energy
Digestion - process of mechanical and chemical breakdown of feed into simple structures

5. Digestive System Simple structures are:
soluble (able to be dissolved) in water
absorbed through mucous membranes lining intestinal tract
membranes that line cavities in the body and connects inside of cavity to outside

6. Digestive System Unique Small, efficient stomach for grain utilization
Large cecum and colon for roughage utilization

7. Digestive System Purpose - process feed into component nutrients for:
Absorption - process of taking in by various means
Utilization

8. Digestive System
Alimentary canal (digestive system) - muscular hollow tube beginning at mouth and ending at anus
Loops on itself many times
Size - One inch in diameter at small intestine to eight inches at large colon

9. Digestive System Component parts include: Mouth Pharynx Esophagus
Stomach
Small intestine
Large intestine
Rectum
Anus

10. Digestive System

11. Digestive System Large intestine consists of the: Cecum
Ventral and dorsal colon
Transverse colon
Small colon
Rectum

12. Digestive System
Alimentary tract with help of teeth, tongue, salivary glands, liver, and pancreas prepare feed for absorption and eliminates waste
Few feeds eaten are in simple forms ready to be absorbed and utilized

13. Digestive System Most feeds require substantial change by:
Mechanical Action
Secretory Action - products produced by glands that aid in digestion
Chemical Action
Microbial Action - digestion by very minute organisms

14. Digestive System Mechanical actions include: Mastication – chewing
Deglutition – swallowing
Intestinal movements
Defecation - elimination of waste

15. Anatomy of the Digestive System

16. Mouth First section of alimentary canal
Contains 24 molars and 12 incisors
Includes tongue and salivary glands

17. Mouth
Prehension -the grasping and moving of feed into the mouth by a sensitive, mobile upper lip
Precise - can graze grass almost into ground
Sorts and selects hay

18. Mouth Digestion - begins in mouth when feed is masticated by the teeth
grinded and chewed by the mouth
Serves to reduce feed particle size

19. Mouth Saliva: 85 pounds (10 gallons) daily
Wets feed - Easier to pass through esophagus
Enzymes - help digest carbohydrates
Produce large amounts only while chewing

20. Pharynx Muscular Funnel shape Guides feed into esophagus
Located in upper back of mouth where digestive and respiratory tracts cross

21. Pharynx
Once feed or water enters pharynx, it cannot return because of blocking action of soft palate
Epiglottis closes at the same time to prevent feed from entering lungs

22. Esophagus 4 to 5 feet in length
Extends from mouth down left side of neck, through the diaphragm, and to the stomach
Moves feed and water to stomach by progressive waves of muscular contractions called peristalsis

23. Esophagus Waves irreversible
Extreme muscle tone occurs at end of esophagus

24. Esophagus Extremely difficult to expel gases through eructation
the act of expelling gas from the stomach through the mouth
Stomach would rupture before vomiting would occur

25. Stomach U-shaped sac near diaphragm at front of abdominal cavity
Sphincter acts as powerful muscle where esophagus enters into stomach
Makes vomiting nearly impossible

26. Stomach Small compared to other animals
10% of total capacity of entire digestive tract
Capacity - two to four gallons
requires they eat two to three times daily rather than just once

27. Stomach Feed moves through rapidly
Frequent feeding in small amounts is more efficient and better satisfies
Rate of passage is rapid in comparison to other areas
Time required for something to move through an area

28. Stomach
Reservoir for ingested feed while subjecting it to gastric digestion
chemical breakdown of feedstuffs by the stomach
Gastric juices, secreted by glands in the mucous membrane of stomach, contain hydrochloric acid, pepsin & gastric lipase

29. Stomach
Pepsin is a protease - enzyme that helps digest protein into amino acids
building blocks of proteins
Gastric lipase - digest fat into fatty acids & glycerol

30. Stomach
When two-thirds full, feed passes into small intestine and continues as eating continues
If horse eats too much at one time, some will leave stomach without sufficient digestive action
Leads to decreased efficiency

31. Stomach Number of digestive disorders can occur Caused by: moldy feeds
ground mashes
sudden changes in feed
feast-and-famine situations
parasites

32. Stomach Very little nutrient absorption takes place in the stomach
Proteins and carbohydrates are only partially digested

33. Small Intestine 2 inch by 60 foot tube Holds approximately 12 gallons
Connects stomach to large intestine
Contains three parts: the duodenum, the jejunum, and the ileum

34. Small Intestine 30% of the digestive tract
Folded into many loops and coils
2.5 to 4 hours for feed to pass

35. Small Intestine Bloodworms cause blood clots
may result in colic or death
tend to lodge in the mesentery artery which supplies blood to the intestines

36. Small Intestine
Small intestine and accessory organs, the pancreas and liver, supply enzymes
Peristalsis mixes fluid contents of the which are about 92-95% water
Pancreatic juices contain the enzymes trypsin, pancreatic lipase, and amylase

37. Small Intestine
Trypsin - converts proteins into amino acids which the small intestine absorbs
Primary site of protein digestion and absorption of amino acids
Pancreatic lipase - breaks down fats to glycerol and fatty acids

38. Small Intestine Liver secretes bile
helps break down fat
aids in fatty acid absorption
activates pancreatic lipase
Most soluble carbohydrates digested in small intestine

39. Small Intestine
End products of carbohydrate digestion are glucose and volatile fatty acids which are absorbed for energy
Absorbs nutrients, such as simple sugars, fatty acids, amino acids, minerals, and vitamins

41. Large Intestine
Composed of the cecum, large colon, small colon, and rectum
Moves undigested materials from small intestine to anus for elimination
50-60% of digestive tract

42. Large Intestine Holds 30-35 gallons 25 feet long
Designed for utilization of plant fiber for energy

43. Large Intestine
After ingesta leaves small intestine, it enters into cecum
substances that have been taken into the body by way of the digestive tract
Cecum serves as fermentation vat in which enzymes break down fibrous plant structures for digestion

44. Large Intestine
Carbohydrates such as cellulose that escaped digestion in small intestine are fermented in large intestine
Complex carbohydrate that is the main component of the plant cell wall

45. Large Intestine
Can digest cellulose, starch, & sugars into volatile fatty acids
supplies up to 25% of horse’s energy

46. Large Intestine Cecum - primary site of water absorption
Rate of passage slower than in other portions of digestive tract
36-48 hours

47. Rectum Connects small colon to anus
Receives feces small colon has formed into characteristic balls
Forty to fifty pounds of feces is voided eight to twelve times a day

48. Rectum
Shape, size, and consistency of feces give clues to overall health
Dry and hard - lack of water or protein
Too soft - Sick or eating diet that is too laxative

49. Digestive System Disorders

50. Disorders
Because of the complex nature of the digestive system, horses are predisposed to digestive disorders
Susceptible to twisting and impaction of the large intestine

51. Disorders Sensitive to gases produced by microbial digestion
Rapid fermentation may cause excessive gas or lactic acid to be produced
can cause colic or laminitis

52. Colic
“Colic” - many painful digestive disturbances with various causes
Improper feeding such as feeding too much grain or suddenly changing the diet can cause colic

53. Colic
Usually caused by gaseous products that are part of microbial digestions
May cause swelling in digestive tract
Ingesting low quality, poorly digestible feed can cause impaction of cecum and colon

54. Colic
To avoid digestive disturbances, allow one to two weeks to change from one feed to another.

55. Laminitis Occurs when inner hoof wall becomes inflamed
Rapid changes in diet can cause certain type of bacteria in cecum to die
Release large amounts of endotoxins

56. Laminitis
Endotoxins enter bloodstream and decrease the amount of blood flow to lamina
Commonly occurs when a horse is switched from winter hay to pasture in the spring

57. Summary
Purpose of digestive system is to process feed into component nutrients for absorption and utilization by the body
Very complex
Many digestive disorders

58. Summary
Monogastric
Eat relatively simple-looking foods that are transformed to an easily digestible form

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part, of this presentation without
written permission is prohibited.
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Texas A&M University
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2008