L44 - Non-ruminant Digestive Physiology

What’s the difference between foregut and hindgut fermentors? Why is this significant?

Foregut → ferment prior to gastric stomach and SI

• VFAs and microbial proteins can be absorbed better in SI

Hindgut → ferment after SI

• VFAs mostly absorbd, but microbial proteins are lost

Where fermentation occurs determines how efficiently nutrients are used

What needs to occur for microbial fermentation?

1. Retention of digesta and microbes

2. Suitable Environment → pH and anaerobic

• Volume for fermentation

• Rention Time → longer retained, more able to digest

• Microbial Population

What’s a key difference between ruminants and hind gut fermentors?

Rention time → less time in hindgut than in ruminants

• Faster in horses than cows

What are foregut formentors? Species?

Stomach compartments sort and retain fibrous materials → 2-4 pouches that are separate from gastric region for “pre-gastric” fermentation

• Expanded cardiac region → microbial fermentation

• Hippos → bulk roughage feeder

• Kangaroo and Sloth → browsers

What are cecal fermentors? Species?

Larger cecum

• Rabbit, guinea pig, rodents

What are colon fermentors? Species?

Large colon

• Horse, elephant, koala

What are the key advantages and limitations of foregut, cecal and colon fermentors?

What domestic species are foregut fermentors?

There are no domestic foregut fermentors (just sloth, kangaroos, wallabies, hippos)

What type of fermentation is useful for degrading plant toxins?

Foregut Fermentor

How many pouches does the stomach of sloth, kangaroos and colobus monkey have?

Sloth: 3 chambers

Kangaroos: Long and tubular with 3 sections (sacciform, tubiform for fiber digestion, and gastric section)

Colobus Monkey: 4 pouches

Why is the cecum considered a blind sac?

Digesta enters and exits through the same opening (approx. 1-2 times a day)

• Separates and excret indigestible fiber based on fiber density in the colon

• Less dense (larger fiber particles) → stay in colon lumen and moves through it

• Denser material (small protein and easily digestible fiber) → collects in colon perimeter → moves back to cecum with fluid for fermentation

• Digestible components are retained

What are the type of feces from a cecal fermenter?

• Hard

  • mostly indigestible fiber

• Soft → “cecotrophs/night feces”

  • mucus-coated by goblet cells

  • comprised of cecal contents

  • recovers B-vitamins and microbial proteins

How do cecal fermentors recovery nutrients?

Coprophagy → eat feces

Why is hindgut fermentation less efficient?

• Fermentation occurs after SI → Microbial protein is lost so can’t be absorbed

• Limited absorption time, but recover most VFAs

What are the functional roles of cecum, haustra and colon?

Cecum → mixes, transports ingesta between haustra

Haustra → sac-like invaginations in cecum and ventral colon

• Keeps digesta homogenous

Colon → fermentation, mixing, bicarbonate secretion, absorption of VFAs and water/electrolytes

What promotes fermentation in the cecum and colon?

Mixing

When do solids vs. soluable digest reach cecum?

Solids → more than 2 hours after ingestion (depends on particle size)

Soluble Digesta → around 2 hours after ingestion

What allows the movement of digesta from cecum to right ventral colon?

Cecocolic orifice

Is there retrograde flow from colon to cecum?

No! Once it leaves, it keeps going!

What are the ventral colon motility types?

1. Haustral Segmentation (mixing) → fermentation and VFA absorption, retention which allows microbes to digest and prevents microbe washout

2. Peristalsis (forward movement) → propels digesta from cecum to left ventral colon

3. Retropulsion → left ventral colon and resists it from moving forward, allows for retention and mixing

What are the dorsal colon motility types?

1. Segmentation

2. Peristaltic

BUT diameter decreases at large and small colon junction → impedes digesta flow → Retropulsion for further mixing

Where is the pelvic flexure?

Left ventral and left dorsal colon

Why is the pelvic flexure clinically relevant?

• Smaller diameter and where antiperistaltic contraction originate → large particles are retained for fermentation → can commonly cause impaction due to flow restriction

What contractions in the small colon allow for the formation of fecal balls?

Segmentation contractions

What is the function of the small colon? Why is this clinically significant?

• Make fecal balls

• Recovers water, electrolytes and VFAs

• Fluxations in water and electrolytes in large/small colon can increase susceptibility to colonic disease in horses

Why are VFAs important?

• Provide energy

• Ex. Acetate, Butyrate, Propionate

What are the typical substrates for fermentation and VFA production?

• Structural carbohydrates → lots of cell walls → high in cellulose and lignin → high amounts reaches hindgut

• Non-structural carbohydrates (starch, soluble sugars, ressistant starches, fructans) → load reaching hindgut varies

  • High NSC can contribute to GI upset (colic or laminitis)

What maintains pH in the colon?

Bicarbonate and phosphate buffers

What is secreted when there’s high VFA production in the colon?W

Water

How are VFAs absorbed? Why is this important?

Sodium co-transport → water follows → bicarb is generated

• Critical for maintaining a stable pH

What’s the transit time of hindgut fermentation?

2-3 days → faster than ruminants

How do foregut and hindgut fermentors compare in regards to efficiency, microbial protein use and transit time?