Ruminant GI Physiology

Question 1

ruminants

Answer 1

animals that regurgitate and remasticate their food

2 suborders: ruminantia and tylopoda

Question 2

fermentative digestion

Answer 2

occurs in specialized compartments localized before the stomach or after the stomach and small intestine

microbes responsible for fermentative digestion are bacteria, fungi, and protozoa

Question 3

ruminal ecosystem

Answer 3

protozoa ingest large numbers of bacteria and hold bacterial number in check

protozoa may also play a role in starch and protein digestion, they prolong the digestion of these substances and protect them from bacterial action

the waste products produced by one species serve as a substrate for another

Question 4

ruminal environment

Answer 4

substrate availability: food intake is regulated by volume, structure, energy, palatability

temperature: about 0.5-1 degree above the body temperature
fluids: water and saliva

pH: 5.5-7

osmolarity: 260 bis>400 mOsm/l

Question 5

plant cell walls

Answer 5

important substrates for fermentative digestion and significant nutrient source for many species

Question 6

carbohydrates

Answer 6

cellulose, hemicellulose, pectin, lignin

all but lignin are not available for absorption by the animal, they are further metabolized by the microbes

Question 7

ruminal layers

Answer 7

gas

fiber mat

intermediate zone

liquid zone

Question 8

products of fermentative digestion

Answer 8

volatile fatty acids

Question 9

major VFAs

Answer 9

acetate, propionate, butyrate

Question 10

what is the only VFA that can be used for gluconeogenesis?

Answer 10

propionate

Question 11

how are proteins broken down?

Answer 11

deamination

Question 12

why are proteins vulnerable to fermentation?

Answer 12

they are made of carbon compounds that can be further reduced to provide energy for anaerobic microbes

Question 13

what do amino acids contribute to?

Answer 13

synthesis of microbial protein

metabolized to VFA and ammonia

Question 14

deamination

Answer 14

amino acid—-> NH3 + carbon skeleton

Question 15

why do ruminants depend on microbial proteins to meet their own needs?

Answer 15

because almost all dietary protein is fermented in the rumen

Question 16

how can protein be produced in the rumen?

Answer 16

protein and nonprotein sources such as ammonia, nitrates, and urea

Question 17

urea recycling

Answer 17

urea is nitrogen waste product of protein catabolism

2 sources in the ruminant: urea coming from deamination of endogenous amino acids excreted in the liver and nitrogen absorbed as ammonia from the rumen

a portion of the urea which is excreted into the rumen can be resynthesized into protein that will contribute eventually to the amino acid needs of the host

Question 18

do microorganisms produce the necessary enzymes for lipid digestion? if so what are they

Answer 18

yes, lipases and phospholipases

Question 19

triglycerides

Answer 19

major lipid type found in cereal grains, oilseeds, animal fats, and byproduct feeds. also present in milk

Question 20

glycolipids

Answer 20

major lipid type found in forages

Question 21

phospholipids

Answer 21

minor component of most feeds. form the cell membrane of all animal cells, and the surface of milk fat globules. important in fat digestion in the small intestine of cows

Question 22

free fatty acids

Answer 22

minor component of dairy feeds, but major component of certain fat supplements

Question 23

how are fats hydrolyzed?

Answer 23

by microbial lipases

Question 24

what does fat hydrolysis result in?

Answer 24

glycerol and sugars and free fatty acids

Question 25

what vitamins do microbes synthesize?

Answer 25

Vitamin C, K, B, thymin, cobalamin

Question 26

absorption in the rumen

Answer 26

2 main mechanisms depending on the ionization state of the VFA ionized need a carrier, non-ionized can diffuse through the apical membrane

Question 27

implication in rumen acidosis

Answer 27

fast fermentable carbs lead to an increase in VFA production--> pH in the rumen drops ionization grade of VFA depends on the pH of the rumen under normal conditions rumen pH is 5.5-7 pK of VFA is 4.8 non-ionized VFA can just diffuse so they will rapidly enter into the rumen epithelium intracellularly, the pH is higher and the VFA can dissociate into Ac- and H+ which represents an additional risk for the cell the acidic pH in the rumen stimulates proliferation of lactate producing bacteria--> exacerbation of the acidosis

Question 28

absorption of sodium, potassium, and chloride in the rumen

Answer 28

sodium: electrogenic transport via sodium channels, electroneutral transport via sodium proton exchanger, basolateral sodium potassium ATPase Chloride: Cl-/HCO3- exchanger, maybe a basolateral exchanger potassium: apical and basolateral channels, high luminal potassium concentration so transepithelial potential difference

Question 29

absorption of calcium and magnesium in the rumen

Answer 29

magnesium: electrogenic transport via magnesium channel, affected in the presence of high potassium concentrations--> pastures grass tetany calcium: reabsorption not fully understood, but probably electroneutral exchange and basolateral sodium calcium exchanger and Ca ATPase

Question 30

what are the forestomachs lined with?

Answer 30

stratified squamous epithelium

Question 31

absorption in the omasum

Answer 31

concentration of the ingesta SCFA absorption Na+ and Cl- absorption HCO3- reabsorption

Question 32

the fate of VFAs in the ruminant

Answer 32

propionate--> liver--> glucose acetate and butyrate--> all tissues--> energy acetate--> adipose tissue--> fatty acids

Question 33

requirements for proper fermentation

Answer 33

substrate for fermentation temperature near 37 osmolality of 300mOsm negative oxidative reduction potential indigestible waste must be removed regeneration of microbes buffer substances

Question 34

primary contractions

Answer 34

the bolus enters the rumen and remains suspended in the area near the cardia biphasic contraction of the reticulum first contraction is weak second is forceful, nearly obliterating the lumen of the reticulum--> bigger particles will be pushed into the dorsal sac caudal moving contraction of the dorsal sac moves ingesta further back into the dorsal sac cranial moving contraction of the dorsal sac mized the ingesta. this ingesta is now under bacterial fermentation which produces a gas. this gas accumulates in the dorsal sac the smaller particles decant into the ventral sac contraction of the ventral sac separates big and small material; small material goes over the cranial pillar into the cranial sac contraction of the cranial sac which further separates material into big and small a new cycle starts, the reticulum contracts, the reticulo-omasal orifice relaxes and small particles are forced through the opening into the omasum

Question 35

function of primary contractions

Answer 35

reduce particle size

Question 36

secondary contractions

Answer 36

function is to force gas toward the cranial portion of the rumen

Question 37

how many contractions per minute

Answer 37

1-3, more frequent during eating and disappear during sleep rate and strength depend on character of the diet

Question 38

what are the main gases produced during rumination?

Answer 38

carbon dioxide and methane

Question 39

eructation frequency

Answer 39

1/min

Question 40

eructation center

Answer 40

localized in the medulla and receives afferent fibers form mechanoreceptors placed in the dorsal sac of the rumen

Question 41

tympanism

Answer 41

bloating occurs when the eructation mechanism fails

Question 42

legume bloat

Answer 42

when cattle feed on lush, rapidly growing alfalfa or clover pastures gas becomes trapped in tiny bubbles and the normal free gas bubble cannot accumulate on top of the dorsal sac of the rumen to the presence of gas is not detectable by the mechanoreceptors

Question 43

ruminant ketosis

Answer 43

occur most frequently in high producing dairy cows, usually within 6 weeks of calving or in late gestation acetate and butyrate enter the TCA cycle as acetyl CoA if there is not enough oxaloacetate or if there is an excess of acetyl CoA, it accumulates and gets degraded to ketone bodies

Question 44

control of reticulorumen motility

Answer 44

ENS and vagus nerve control center is in the brain stem as the dorsal vagal nucleus stretch receptors and chemoreceptors monitor distention, consistency of the ingesta, pH, VFA concentration, ionic strength

Question 45

esophageal groove

Answer 45

gutter like invagination traversing the wall of the reticulum from the cardia to the reticulo-omasal orifice diverts milk away from the developing rumen and passes it directly to the abomasum closure is a relfex action

Question 46

hindgut fermentation

Answer 46

horses rely on fermentation in the colon to cover their energy needs

Question 47

substrates for hindgut fermentation

Answer 47

structural and nonstructural carbohydrates as well as proteins fermentation products are VFA and absorption mechanisms are similar to that observed in ruminants

Question 48

conditions for maintaining fermentation

Answer 48

substrate supply control of pH osmolality anaerobiosis retention of fermenting material removal of waste product and residue

Question 49

predominant motility patterns in ventral colon

Answer 49

haustral segmentations, propulsive peristalsis, retropulsive peristalsis

Question 50

the principal end products of dietary carbohydrates in ruminants are? A. triglycerides B. glucose C. amino acids D. VFAs

Answer 50

D

Question 51

which of the following is a component of rumination? A. vomiting B. eructation C. flatulence D. regurgitation

Answer 51

D

Question 52

the 2 major motility patterns observed in the rumen are A. peristaltic and antiperistaltic waves B. segmentation and propulsive contractions C. mixing and eructation contractions

Answer 52

C

Question 53

deglutition, eructation, and regurgitation can be observed on the left side of a cow A. true B. false

Answer 53

A

Question 54

comparing forestomach versus hindgut fermentation which is true? A. the microbial populations are different but the products are the same B. microbial populations are the same but the products are different C. both microbial populations and products are similar

Answer 54

C

Question 55

How do ruminants get glucose needed for energy?

Answer 55

all glucose available to ruminants originates from gluconeogenesis, the most important precursor being propionate

Question 56

succinate

Answer 56

4 carbon intermediate that can lead to the formation of oxaloacetate which is the entry metabolite from gluconeogenesis

Question 57

special considerations for glucose homeostasis in ruminants

Answer 57

ruminants exist in a constant state of potential glucose deficiency gluconeogenesis covers most of the glucose needs insulin levels are regulated by the concentration of SCFAs all the glucose available to ruminants originates from gluconeogenesis. the most important precursor of glucose in ruminants is the VFA propionate almost all propionate absorbed from the rumen is extracted from the portal blood by the liver and never enters the systemic circulation ruminants also efficiently conserve glucose. in ruminants, fatty acids are synthesized only in adipose tissues using acetate as a precursor molecule and never glucose in high producing dairy cows, nearly all the glucose they produce goes to lactose; the remaining tissues function on alternative fuels

Question 58

concerning protein fermentation in the rumen, which of the following is correct? A. endopeptidases are of host's origin B. peptides and amino acids can be used by microbes to synthesize microbial protein C. both are right

Answer 58

B

Question 59

which of the following vitamins is not synthesized by ruminal microbes? A. vitamin B12 B. vitamin K C. vitamin D D. vitamin C

Answer 59

C

Question 60

which of the following concerning ruminal motility is true? A. biphasic contractions of the reticulum occur in the beginning of the cycle B. the function of primary contractions is to reduce particle size C. the function of secondary contractions is to force has toward the cranial portion of the rumen D. all of the above is correct

Answer 60

D

Question 61

eructation is activated by mechanoreceptors located in the ventral sac of the rumen A. true B. false

Answer 61

B

Question 62

bloat in cattle is caused by A. an increase in the volume of gas produced B. a failure of the eructation mechanism

Answer 62

B

Question 63

regurgitation occurs before the regular biphasic contraction of the reticulum A. true B. false

Answer 63

A