Ruminant Digestion

Question 1

What are the four chambers of the ruminant stomach?

Answer 1

Fore-stomach: rumen, reticulum, omasum
True stomach: abomasum

Question 2

What comprises the rumen microbiota?

Answer 2

Bacteria, protozoa and fungi

Question 3

What is the rumen comprised of?

Answer 3

1. Cranial sac, ventral sac, and ventral blind sac.
2. Wall is covered with many finger-like projections known as papillae.

Question 4

Describe the role of the abomasum.

Answer 4

1. Analogous to the monogastric’s stomach.
2. Secretes gastric enzymes and HCl.

Question 5

What causes closure of the oesophageal/ventricular groove and describe its function.

Answer 5

Sucking and chemoreceptors in pharynx sensitive to milk compounds; allows milk to bypass rumen and enter the omasum.

Question 6

Name the 3 volatile fatty acids produced.

Answer 6

Acetate, butyrate and propionate

Question 7

How are the gases produced by fermentation expelled?

Answer 7

Eructation

Question 8

Describe the distribution of food/particles in the rumen/reticulum.

Answer 8

1. Heavy substances such as grains, rocks, or nails settle into the reticulum.
2. In rumen: gas (upper), lighter roughage pieces (middle), and grain and fluid saturated roughage (bottom).

Question 9

Why is remastication/reinsalivation important?

Answer 9

Saliva is a significant buffering agent –> vital for maintaining optimum rumen pH.

Question 10

What happens to the little amount of oxygen released into rumen?

Answer 10

Utilised by facultative anaerobes to maintain anaerobic conditions.

Question 11

Describe the primary contraction of the rumen.

Answer 11

1. Includes two contractions of the reticulum, which reaches the rumen.
2. Leads to the ingesta flow from reticulum to cranial ruminal sac and later to ventral sac.

Question 12

Describe the secondary contraction of the rumen.

Answer 12

1. Causes eructation
2. Leads to the ingesta flow from the caudo-ventral blind sac to the dorsal blind sac followed by dorsal sac (causes eructation) and ventral sac in sequence.

Question 13

What are rumen bacteria categorised into?

Answer 13

Cellulolytic and amylolytic

Question 14

Describe the rough percentage makeup of the rumen micro-organisms.

Answer 14

• Most bacteria (50-90%), then protozoa (10-50%), and remaining fungi.
• Protozoa much larger therefore contribute almost equally to microbial mass.

Question 15

What is the role of rumen fungi?

Answer 15

Able to degrade lignin to a certain extent.

Question 16

List the speed of fermentation of structural and non-structural carbohydrates.

Answer 16

1. Carbs in roughages are structural and include cellulose, semi-cellulose, lignin and pectin. Slowly fermented.
2. Starch in concentrates are non-structural and less rapidly fermented.
3. Soluble sugars are rapidly fermented.

Question 17

Why are matured forages less digestible?

Answer 17

Higher proportion of lignin.

Question 18

Describe the difference in end-products of a roughage vs concentrate diet.

Answer 18

Roughage rich –> production of acetate at higher proportion
Concentrate rich –> higher amount of propionate

Question 19

What do amylolytic bacteria primarily metabolize?

Answer 19

Starch and other soluble carbohydrates.

Question 20

What are the main products of glucose fermentation by amylolytic bacteria?

Answer 20

Volatile fatty acids (acetate, propionate, and butyrate), lactic acid, and gases (CO₂, H₂).

Question 20

Which VFA produced by amylolytic bacteria is a precursor for gluconeogenesis?

Answer 20

Propionate

Question 21

What condition can result from rapid starch fermentation by amylolytic bacteria?

Answer 21

Rumen acidosis due to lactic acid accumulation.

Question 22

What do cellulolytic bacteria primarily metabolize?

Answer 22

Cullulose, hemi-cellulose, fructosans, pectin (β-glycosidic bonds)  monosaccharides

Question 23

What happens to cellulolytic bacteria if the rumen pH drops too low?

Answer 23

Their activity decreases, impairing fiber digestion.

Question 24

What types of carbohydrates do protozoa metabolize?

Answer 24

Starch, soluble sugars, and partially degraded fiber.

Question 25

What are rumen degradable proteins (RDP)?

Answer 25

Proteins that are broken down by rumen microbes into ammonia, amino acids, and peptides.

Question 26

What are rumen undegradable proteins (RUP)?

Answer 26

Proteins that bypass rumen fermentation and are digested in the abomasum and small intestine.

Question 27

How do microbes in the rumen utilize protein?

Answer 27

Microbes break down RDP into ammonia and use it, along with energy, to synthesize microbial protein.

Question 28

What happens to microbial protein after it is synthesized in the rumen?

Answer 28

It passes to the abomasum and small intestine, where it is digested and absorbed as amino acids.

Question 29

What is the importance of urea in ruminants?

Answer 29

Urea can be recycled back to the rumen via saliva or blood and used as a nitrogen source for microbes.

Question 30

What happens to dietary lipids in the rumen?

Answer 30

Lipids undergo hydrolysis and biohydrogenation by rumen microbes.

Question 31

What is hydrolysis in the context of lipid digestion?

Answer 31

Microbial lipases break down triglycerides and glycolipids into free fatty acids, glycerol, and sugar moieties.

Question 32

What is biohydrogenation?

Answer 32

The process by which unsaturated fatty acids are hydrogenated to form saturated fatty acids by rumen microbes.

Question 33

What happens to glycerol and sugars released during lipid hydrolysis?

Answer 33

They are fermented by rumen microbes to produce volatile fatty acids.

Question 34

What is the fate of fatty acids after the rumen?

Answer 34

Fatty acids pass to the small intestine for absorption as micelles.

Question 35

Describe the motility of regurgitation.

Answer 35

1. Initiated with a reticular contraction distinct from the primary contraction.
2. This contraction, in conjunction with relaxation of the distal esophageal sphincter, allows a bolus of ingesta to enter the esophagus.
3. The bolus is carried into the mouth by reverse peristalsis.

Question 36

Define proteolytic bacteria.

Answer 36

These bacteria degrade proteins into peptides and amino acids.