Lecture 10 - Ruminant Physiology

Question 1

3 modes of motility of the reticulo-rumen

Answer 1

1. mixing
2. eructation = burping, getting rid of gas that is a product of fermentation
3. rumination = bringing up cud to rechew

Question 2

The rumen doesn’t have villi, what does it have?

Answer 2

• Papillae

Question 3

Rumen papillae

Answer 3

• have highly vascularized connective tissue, but lacks smooth muscle, therefore don’t move
• cells in contact with contents are keratinized and dead (stratified squamous epithelium)
• cell renewal takes place in stratum basale

Question 4

What is the rumen a large compartment for? (main fxn)

Answer 4

microbial fermentation

Question 5

Where are rumen papillae found?

Answer 5

• ventral part of rumen

Question 6

What are the 2 sensory receptors found in the rumen?

Answer 6

1. Tension receptors: excited by passive distention
2. Epithelial receptors: excited by physical and chemical stimuli

Question 7

What kind of the environment is the rumen?

Answer 7

moist and warm; suitable for fermentation

Question 8

What is the pH of the rumen?

Answer 8

• 5.5 to 7.1 (fairly neutral)
• buffered (able to keep this pH) due to saliva

Question 9

Why does eructation need to occur?

Answer 9

• when microbes ferment they produce gas (ex. methane, CO2)

Question 10

What happens to fermentation end products?

Answer 10

They are absorbed
- SCFA = acetate, propionate, butyrate
- papillae increase SA for absorption

Question 11

Reticulum (“tripe”)

Answer 11

• stratified squamous epithelium (layers similar to rumen)
• honeycombed appearance
• partially separated from the cranial sac of the rumen
• rumen and reticulum are anatomically different, but operate as a combined fxnl unit

Question 12

What does contraction of the reticulum facilitate?

Answer 12

1. regurgitation for rumination
2. mixing digesta in the reticuluo-rumen
3. passage of digesta to the omasum

Question 13

What is the purpose of the reticular groove?

Answer 13

• a conduit for milk from cardiac opening to the reticulo-omasal opening, then through the omasum to abomasum; closes over as the calf is suckling so milk is kept out of the rumen and isn’t fermented
• closure of groove is a reflex initiated when receptors in the mouth and pharynx are stimulated

Question 14

Omasum

Answer 14

• when particle size is small enough it will travel from the reticulum to the omasum
• reticulo-omasal orifice works as a bottleneck for the digesta outflow to the abomasum
• stratified squamous epithelium
• consists of many leaves (laminae)
• absorption of water and VFA

Question 15

Main fxn of omasum

Answer 15

absorption of water and VFA

Question 16

Abomasum

Answer 16

• true stomach secreting hydrochloric acid and enzymes
• mucosal epithelial cells

Question 17

Steps for mixing (via contractions) of the reticulo-rumen

Answer 17

1. starts with double (biphasic) contraction in reticulum
2. anterior dorsal sac of rumen
3. caudal region of rumen
4. main ventral rumen
5. caudoventral sac

Question 18

What does rumen contraction enhance? Why?

Answer 18

• VFA absorption
• after mixing digesta, VFA are redistributed evenly close to papillae absorptive surface

Question 19

4 rumen content layers

Answer 19

1. Gas Layer
2. Fiber Mat (intense fermentation)
3. Intermediate Zone (intense fermentation)
4. Liquid zone (moderate fermentation)

Question 20

Eructation of the reticulo-rumen

Answer 20

1. starts in caudoventral blind sac
   2-4. sweeps across the dorsum to reach vicinity of the cardia (pushing the gas bubble at the top to the front)
2. completed with contraction of the main ventral rumen

*distention of dorsal rumen by gas
* gas “bubble” is pressed against cardia and is forcibly ejected into esophagus by contraction of main ventral rumen

Question 21

What side do we puncture for bloat?

Answer 21

LEFT

Question 22

Rumination of reticulo-rumen

Answer 22

• coordinated series of events involves respiratory muscles, larynx, pharynx, esophagus, buccal apparatus, and reticulum

Question 23

What happens during the additional reticular contraction preceding biphasic contraction?

Answer 23

• Why? to remove newly swallowed content from opening of esophagus
• during extra contraction soft palate is elevated closing nasal passage
• at the same time the contraction of the inspiratory m. expands the thorax to draw contents into esophagus
• reverse peristalsis lifts bolus into buccal cavity
• tongue presses out liquid and re-swallowed
• re-mastication and re-insalivation
• full rumination sequence usually followed by another

Question 24

How many rumination periods occur within 24 hours?

Answer 24

• evenly distributed up to 14 periods/24h

Question 25

What influences time of rumination?

Answer 25

• Cattle on hay: 8hr/d
• Cattle on concentrates: 2.5/d
• Long vs chopped hay: short = less rumination = less buffering = risk of acidosis

Question 26

Rank the fermentability of sugar, starch and fiber

Answer 26

sugar > starch > fiber

Question 27

What does excess ruminal fermentation result in?

Answer 27

• greater fermentation acid production (VFA and lactate)

Question 28

Rumination stimulates saliva secretion which is good why?

Answer 28

saliva contains buffer and helps maintain stable ruminal environment

Question 29

What is ruminal pH determined by?

Answer 29

• the balance btw VFA production and buffering capacity of rumen (saliva secretion)

Question 30

What CHOs get fermented? What are the products?

Answer 30

Fermented: starch, fiber, sugar, pectin
Products: acetate, propionate, butyrate, CO2, CH4

Question 31

How is the composition and abundance of VFA affected by diet?

Answer 31

• High fiber diet vs high starch (concentrate) diet
• Lots of concentrate = increase in total SCFA production, more propionate (which is the most energetically efficient bc we are not losing CO2)

Question 32

Why is propionate the most energetically efficient SCFA?

Answer 32

• not losing CO2 in the process

Question 33

What happens if you change from a forage to concentrate diet?

Answer 33

• increase in propionate initially but it can start to drop off and you get a big increase in lactate
• low pH = risk of acidosis

Question 34

Metabolic fate of acetate

Answer 34

• energy source in most tissues
• substrate for FA synthesis in adipose tissues and mammary gland
• not used for glucose synthesis

Question 35

Metabolic fate of propionate

Answer 35

• primarily taken up by the liver to produce glucose

Question 36

Metabolic fate of butyrate

Answer 36

• utilized by ruminal wall as an energy source, and ketones produced from butyrate in ruminal wall serve as energy source and substrate for FA synthesis

Question 37

What does poor quality hay result in?

Answer 37

• slows down rumen emptying into the omasum
• affects overall digestibility