Rumen Motility

Question 1

Rumen turnover

Answer 1

-time required to replace the rumen contents with an equivalent volume
*mostly influenced by salivation and drinking

Question 2

Fluid input

Answer 2

-saliva
-drinking
-H2O movement across rumen wall

Question 3

Fluid output

Answer 3

-H2O absorption (across rumen wall)
-Passage to omasum

Question 4

Rumen fluid turnover speed

Answer 4

-High forage: faster (3-7 times per day)
-high concentrate: slower (2-3 times/day)

Question 5

Solid turnover

Answer 5

-rate of loss of solid material

Question 6

Factors affecting solid turnover

Answer 6

1.feed digestibility (grain 90%, forage 50%)
2.feed intake
>increased intake=increased rumen distension and increased motility
>increased motility=decreased time for fermentation
3.Particle size (smaller=less retention)

Question 7

Turnover effects on efficiency

Answer 7

-more turnover results in more substrate for bacteria and therefore an increase in VFA production. Overall increase in feed efficiency

Question 8

Why does turnover increase efficiency?

Answer 8

-favours faster growing bacteria (more protein produced)
-more bacteria in exponential growth phase making the bacteria more efficient and produce more VFAs
-increased dilution rate results in a decrease in protozoa which eat the bacteria (washed away with rumen contents)

Question 9

Rumen motility

Answer 9

-rhythmic contractions of the reticulorumen

Question 10

Functions of rumen motility

Answer 10

1.continuous mixing of contents
2.inoculation of feed particles with microbes
3. particle sorting (size)
4. rumination (chewing cud=more mechanical digestion)
5. Eructation (elimination of gas from fermentation)

Question 11

Importance of continuous mixing of contents

Answer 11

-mixes with saliva resulting in buffering
-prevents pockets of high concentration
-contact with epithelium results in absorption

Question 12

Primary contraction cycle

Answer 12

-major mixing cycle
-occurs ~1 per min and lasts 20secs
-loud

Question 13

Primary contraction cycle steps

Answer 13

1.Biphasic (double) contraction of reticulum
2. Contraction of cranial sac and cranial pillar
3. contraction of dorsal sac (cranial to caudal)
4. Contraction of ventral sac (cranial to caudal, then caudal to cranial)
5.Relaxation of cranial pillar (digesta can move into reticulum)

Question 14

Primary contraction cycle frequency

Answer 14

-Eating: 35-45 secs
-Ruminating: 45-60secs
-Resting: 60-90secs

Question 15

Secondary contraction cycle

Answer 15

-occurs once every two primary cycles
-not as loud
-release of the gas produced from fermentation (30-50L/hour in cattle) through the contractions that tilt the gas pocket forward to cardia and into esophagus

Question 16

Secondary contraction cycle steps

Answer 16

1.Primary contraction steps
2.Contraction of caudoventral blind sac
3.Cranial-moving contraction of the caudodorsal blind sac
4.Contraction of ventral sac

Question 17

Gas stimulation at cardia

Answer 17

-Triggers the relaxation of cardia and lower esophageal sphincter. Will not relax if fluid/digesta is present.
>Reason that frothy bloat occurs and bovine cannot get rid of

Question 18

Inhalation pressure change

Answer 18

-Results in negative pressure in the esophagus
>Gas travels up into esophagus
>Some gas expired directly
>Majority inspired into trachea/lungs first. Expired on next breath and some gas can be absorbed into blood

Question 19

Rumination

Answer 19

-regurgitation of digest from reticulum
>large particle size, low density is moved up and out. Allows for mechanical breakdown through chewing cud

Question 20

Rumination contraction

Answer 20

-occurs just before primary or secondary contraction cycle
-triphasic

Question 21

Rumination steps

Answer 21

1.relaxation of cardia and esophageal sphincter allowing bolus to enter esophagus
2.Reverse peristalsis of esophagus moves the bolus to the mouth
3.Tongue squeezes out liquid and mastication and salivation occurs
4. Swallowed again

Question 22

Rumination time length

Answer 22

-Cud (bolus) is chewed for 10-60secs which increased salivation and therefore buffering
-up to 10hours per day

Question 23

Rumination stimulation

Answer 23

-stimulated by long-stem fibers rubbing rumen epithelium
*more fiber=more rumination

Question 24

Control of motility

Answer 24

-no autonomous smooth muscle contractions
-no cells of cajal and no pacemakers

Question 25

Intrinsic nerve plexi and ruminant contractions

Answer 25

-Do not produce organized contractions for ruminant motility
- has low amplitude variations in smooth muscle tone
-may excite tension receptors which stimulates extrinsic motility

Question 26

Vagus nerve role in rumen motility

Answer 26

-Most important for ruminant motility
-Vagus is a parasympathetic NS with multiple branches into areas of reticulum and rumen
>responsible for both primary and secondary contraction

Question 27

Splanchnic nerve

Answer 27

-sympathetic NS
-inhibits motility
-much smaller role in vagus nerve

Question 28

What controls the vagus nerve and its impact on rumen motility?

Answer 28

-controlled by gastric centers of the medulla (bilateral)

Question 29

Vagus nerve effects

Answer 29

-affects frequency, duration, and amplitude of motility

Question 30

Vagus nerve activation

Answer 30

-dependent on balance of excitatory and inhibitory signals from receptors

Question 31

Stimulatory control of gastric centers

Answer 31

1.Buccal mechanoreceptors- eating and chewing
2.Rumen tension receptors- mild to moderate stretch
3. Rumen epithelial (mucosa) receptors- touch (rubbing or large particles against rumen epithelium)

Question 32

Inhibitory control of gastric centers

Answer 32

1.High threshold tension receptors in reticulum and cranial sac (severe stretch, eg. Bloat)
2.Tension receptors in abomasum (reduce throughout of material into omasum)
3. Rumen epithelial receptors detecting acid (will result in reduced motility, fermentation and acid production)
4.Pain (abdominal/visceral pain)
5. Medications (sedatives, tranquilizers, eg. Xylazine alpha-2 agonists)

Question 33

Rumen tension receptor location

Answer 33

-located in smooth muscle of rumen

Question 34

Rumen tension receptors during low to moderate distension

Answer 34

-excites tension receptors
-stimulates gastric centers
-increased motility

Question 35

Rumen tension receptors during severe distension

Answer 35

-inhibits gastric centers= reduced motility
-mechanism is not known
>separate high tension receptors?
>gastric centers respond differently to high rates of tension receptor firing

Question 36

Rumen epithelial receptor location

Answer 36

-located in epithelial lining of the rumen

Question 37

Rumen epithelial receptors and mechanical stimulation

Answer 37

-light touch
>rubbing of long fibers against epithelium
>stimulates salivation and rumination

Question 38

Rumen epithelial receptors and chemical stimulation

Answer 38

-low pH in rumen
>inhibitory signals to gastric centers
>decreases rumen motility
-low pH in abomasum (eg. When empty)
>stimulatory signals to gastric centers
>increased rumen motility