Exam 4 (Lecture 49) - Hindgut Fermentation

Question 1

Name the two main structures of the equine hindgut.

Answer 1

1) Cecum

2) Colon

Question 2

Fermentative digestive process in the _________ is not as efficient as in the ___________. However, the physiology is very similar.

Answer 2

Horse; ruminant

Question 3

List the conditions required for optimal hindgut fermentation.

Answer 3

1) Substrate supply

2) Control of pH and osmolality

3) Numerous and diverse types of anaerobic microbes

4) Retention of fermenting material

5) Continual removal of residue and waste products

Question 4

Name the substrate (CHO/cellulose, protein, or fat) required for hindgut fermentation.

Answer 4

CHO/cellulose

Question 5

_____________ and related molecules pass through the small intestinal tract. Plant material may be softened and swollen prior to entry into the cecum.

Answer 5

Cellulose

Question 6

A large quantity of __________ generated in the equine large colon is wasted because there is no opportunity for absorption of amino acids.

Answer 6

Microbial crude protein (MCP)

Question 7

Hindgut fermentation is aided by the effects of soaking and acid exposure on plant particles in the ___________. Increases susceptibility to microbial action which _________ rate of digestion in the hindgut.

Answer 7

Stomach

Increases

Question 8

How do the microbes acquire N for fermentation?

Answer 8

1) There is extensive N recycling into the colon and cecum (like in the rumen)

2) Urea plus protein escaping SI digestion supplies the N needs of the microbes

3) Horses DO NOT have an efficient means of recovering microbial protein synthesized in the hindgut
- so most is passed in feces

Question 9

Mixing action (segmentation) of the _________ maintains the cecal contents in a homogenous state.

Answer 9

Cecum

Question 10

Briefly describe the type of motility pattern located in the cecum (slide 5).

Answer 10

1) About once every 3-4 minutes there is a strong contraction of cecal muscles in a mass peristaltic movement type of action

2) Body and apex of the cecum shorten and constrict lifting ingesta into the base

3) Constriction of cecal base forces material through the ceco-colic oriface and into the RVC

4) Motility pattern functionally separates the cecum from the ventral colon

5) Horses DO NOT have retrograde flow of material from the colon back into the cecum

Question 11

Briefly describe the two types of motility patterns located in the right and left ventral colon.

Answer 11

1) Haustral Segmentation:
- Mixing with no net forward movement
- Serves a mixing function that aids in promoting fermentation and bringing VFAs in contact with mucosa
for absorption
- Mixing occurs throughout the ventral colon
- RVC and LVC segments are regarded as one functional unit with homogeneous ingesta

2) Peristalsis:
- Propulsive
- Aboral peristalsis
- Ventral colon originates near the cecum and appears to occur as a continuation of the cecal mass
movements

Question 12

Briefly describe the type of motility pattern located in the left ventral colon.

Answer 12

1) Retropulsive or anti peristaltic movements resist the flow of ingesta

2) Movement proceeds cranial (oral) or caudal (aboral) depending on pacemaker origin (ICCs)

3) Result in the retention and mixing of material in the ventral colon

4) Allows time for microbial digestion and preventing the washout of microbes

Question 13

What is the function of the pelvic flexure?

Answer 13

Impedes movement of ingesta, causing it to be retained in the ventral colon

Squeezing action selectively retains relatively large particulate matter
- allows liquid and small particles to pass

Question 14

As particle size __________, there is significant __________ of material in the colon and _________ passage to the feces. (Graph, slide 10).

Answer 14

Increases; retention; slow

Question 15

The equine hindgut requires an efficient means of buffering and VFA absorption. Large quantities of fluid, rich in _________ and _________ buffers are secreted by the ileum and transferred to the cecum.

Answer 15

HCO3- and PO4-

Question 16

Large fluxes of ____________ traverse the cecal and colonic mucosa during the course of digestion. When horses are meal-fed, feed starts to enter the cecum about 2 hours after eating, and _________ production begins rapidly.

Answer 16

Water

VFA

Question 17

During the period of active VFA production, large quantities of water enter the hindgut from the blood through the mucosa. Considerable ___________ and __________ movement of water occurs across the mucosa in each of the major fermentation compartments.

Answer 17

Inward; outward

Question 18

Inward (into the lumen) water movement results from mucosal secretion, whereas outward water movement occurs in association with absorption of ____________.

Answer 18

VFAs

Question 19

Molecular mechanisms of VFA absorption in the equine colon appear to be identical to those in the ____________. Large water and electrolyte fluxes in the colon make horses vulnerable to colonic diseases, resulting in fluid and electrolyte losses.

Answer 19

Rumen

Question 20

What is the function of the small colon?

Answer 20

Recover water, electrolytes, and VFAs that were not absorbed in the large colon

Question 21

Briefly describe rabbit cecal fermentation and the importance of cecotrophy.

Answer 21

1) Diet of course hay and pellet fiber are fermented by microbes into cecal pellets

2) Cecotrophy (consuming cecal pellets) important because they contain:
- Amino acids
- Essential fatty aicds
- Vitamins (especially B and K)
- These get absorbed in the small intestine