Ruminant GI Physiology Flashcards
ruminants
animals that regurgitate and remasticate their food
2 suborders: ruminantia and tylopoda
fermentative digestion
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
ruminal ecosystem
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
ruminal environment
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
plant cell walls
important substrates for fermentative digestion and significant nutrient source for many species
carbohydrates
cellulose, hemicellulose, pectin, lignin
all but lignin are not available for absorption by the animal, they are further metabolized by the microbes
ruminal layers
gas
fiber mat
intermediate zone
liquid zone
products of fermentative digestion
volatile fatty acids
major VFAs
acetate, propionate, butyrate
what is the only VFA that can be used for gluconeogenesis?
propionate
how are proteins broken down?
deamination
why are proteins vulnerable to fermentation?
they are made of carbon compounds that can be further reduced to provide energy for anaerobic microbes
what do amino acids contribute to?
synthesis of microbial protein
metabolized to VFA and ammonia
deamination
amino acid—-> NH3 + carbon skeleton
why do ruminants depend on microbial proteins to meet their own needs?
because almost all dietary protein is fermented in the rumen
how can protein be produced in the rumen?
protein and nonprotein sources such as ammonia, nitrates, and urea
urea recycling
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
do microorganisms produce the necessary enzymes for lipid digestion? if so what are they
yes, lipases and phospholipases
triglycerides
major lipid type found in cereal grains, oilseeds, animal fats, and byproduct feeds. also present in milk
glycolipids
major lipid type found in forages
phospholipids
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
free fatty acids
minor component of dairy feeds, but major component of certain fat supplements
how are fats hydrolyzed?
by microbial lipases
what does fat hydrolysis result in?
glycerol and sugars and free fatty acids
what vitamins do microbes synthesize?
Vitamin C, K, B, thymin, cobalamin
absorption in the rumen
2 main mechanisms depending on the ionization state of the VFA
ionized need a carrier, non-ionized can diffuse through the apical membrane
implication in rumen acidosis
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
absorption of sodium, potassium, and chloride in the rumen
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
absorption of calcium and magnesium in the rumen
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
what are the forestomachs lined with?
stratified squamous epithelium
absorption in the omasum
concentration of the ingesta
SCFA absorption
Na+ and Cl- absorption
HCO3- reabsorption
the fate of VFAs in the ruminant
propionate–> liver–> glucose
acetate and butyrate–> all tissues–> energy
acetate–> adipose tissue–> fatty acids
requirements for proper fermentation
substrate for fermentation
temperature near 37
osmolality of 300mOsm
negative oxidative reduction potential
indigestible waste must be removed
regeneration of microbes
buffer substances
primary contractions
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
function of primary contractions
reduce particle size
secondary contractions
function is to force gas toward the cranial portion of the rumen
how many contractions per minute
1-3, more frequent during eating and disappear during sleep
rate and strength depend on character of the diet
what are the main gases produced during rumination?
carbon dioxide and methane
eructation frequency
1/min
eructation center
localized in the medulla and receives afferent fibers form mechanoreceptors placed in the dorsal sac of the rumen
tympanism
bloating
occurs when the eructation mechanism fails
legume bloat
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
ruminant ketosis
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
control of reticulorumen motility
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
esophageal groove
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
hindgut fermentation
horses rely on fermentation in the colon to cover their energy needs
substrates for hindgut fermentation
structural and nonstructural carbohydrates as well as proteins
fermentation products are VFA and absorption mechanisms are similar to that observed in ruminants
conditions for maintaining fermentation
substrate supply
control of pH
osmolality
anaerobiosis
retention of fermenting material
removal of waste product and residue
predominant motility patterns in ventral colon
haustral segmentations, propulsive peristalsis, retropulsive peristalsis
the principal end products of dietary carbohydrates in ruminants are?
A. triglycerides
B. glucose
C. amino acids
D. VFAs
D
which of the following is a component of rumination?
A. vomiting
B. eructation
C. flatulence
D. regurgitation
D
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
C
deglutition, eructation, and regurgitation can be observed on the left side of a cow
A. true
B. false
A
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
C
How do ruminants get glucose needed for energy?
all glucose available to ruminants originates from gluconeogenesis, the most important precursor being propionate
succinate
4 carbon intermediate that can lead to the formation of oxaloacetate which is the entry metabolite from gluconeogenesis
special considerations for glucose homeostasis in ruminants
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
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
B
which of the following vitamins is not synthesized by ruminal microbes?
A. vitamin B12
B. vitamin K
C. vitamin D
D. vitamin C
C
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
D
eructation is activated by mechanoreceptors located in the ventral sac of the rumen
A. true
B. false
B
bloat in cattle is caused by
A. an increase in the volume of gas produced
B. a failure of the eructation mechanism
B
regurgitation occurs before the regular biphasic contraction of the reticulum
A. true
B. false
A
