Basic ruminants
The reticulum vs rumen?
reticulum = No sphincter separating the reticulum from the rumen, allows small digesta particles to move to omasum, traps heavy objects, contraction form esophageal groove in neonates
Rumen = microbial fermentation, large volume, lined with papillae (for surface area and absorption)
What is stratification?
Layers form based on particle density and size
low density fiber raft - rumination and fermentation
Light large particles on top, Medium density small particles in middle, Very dense particles on bottom
What controls gastric secretions?
Stimulatory signals - buccal mechanoreceptors, rumen tension receptors, rumen epithelial mechanoreceptors, abomasal chemoreceptors
inhibitory signals - high threshold tension receptors in reticulum and rumen, tension receptors in abomasum, rumen epithelial chemoreceptors, pain, medications
What affects rumen pH?
Diet - high forage = neutral, high concentrate = 4.9-6
feed processing - Chopping & grinding reduces particle size which lowers rumen pH
feed intake - going from restriction to full intake - drops pH by ~1 full unit
Time - pH is lowest 3-4 hours after feeding - more frequent meals = less pH flucuation
What is the gas composition that the rumen produces?
CO2 - 65% (decarboxylation and carbonic anhydrase)
CH4 - 25% (methanogens, energy is lost when CH4 is produced, ionophores reduce CH4 production)
N2 - 7%
O2 - 0.5% (used up rapidly by facultative anaerobes
H2 - 0.2% (H mostly as H+ ions in solution
H2S - 0.01%
the Omasum vs abomasum?
O = Water absorption, volatile fatty acid absorption, electrolyte absorption, many leaves
A = Glandular "true" stomach, secretes HCl (pH 2.5-3.5), digestive enzymes (pepsin and lysozyme)
1 degree contraction cycle?
Major mixing cycle, loud, occurs ~1/min
Biphasic contraction of reticulum, contraction of cranial sac and cranial pillar, contraction of dorsal sac, contraction of ventral sac, relaxation of cranial pillar
Rumen tension receptors vs rumen epithelial receptors?
Tension = located in muscle wall, low to moderate distension (excites tension receptors, stimulates gastric centers, increased motility), Severe distension (inhibits gastric centers = reduced motility, mechanism is not known)
Epithelial = located in the epithelial lining of the rumen, mechanoreceptors (light touch), chemoreceptors (low pH in rumen, low pH is abomasum)
What does an abnormal pH do to the rumen?
Effects motility
effects microbes
Acute acidosis
sub-acute ruminal acidosis
Gas production within the rumen?
Product of microbial fermentation
Maximum occurred ~2-4 hours after a meal
cattle = 30-50L/hour or 400L/day
eliminated by eructation
bloat can occur very quickly
What are the benefits of ruminant fermentation?
More extensive and efficient fermentation - able to break down fibrous plant material
Rumination = more mastication
Microbial proteins = from plant protein and non-protein nitrogen
B vitamins can be absorbed in small intestine
Detoxification of plant compounds
2 degree contraction cycle
occurs once for every 1 degree cycles, release of gas produced from fermentation, contractions tilt gas pocket forward which allows gas to be released - begins with same steps as 1 degree
Biphasic contraction of reticulum, contraction of cranial sac and cranial pillar, contraction of dorsal sac, contraction of ventral sac, contraction of caudoventral blind sac, contraction move cranially through caudodorsal blind sac, contraction of ventral sac
How to evaluate motility?
Visual - chewing cud
Palpation - left paralumbar fossa = should be soft
listening - stethoscope in left paralumbar fossa, rumbling, splashing or tinkling, percussion
How to test rumen pH?
Through a stomach tube - this risks saliva contaminations and fluctuations
sensor bolus - given orally so it stays in the rumen, lasts 3-5 months, records daily patterns
What is rumen turnover?
Fluid vs solid
fluid turnover - inputs (saliva, drinking, H2O movement across rumen wall), outputs (H2O absorption, passage to omasum), high forage = faster, high concentrate = slower, mostly influences by salivation and drinking
What are the disadvantages of ruminant fermentation?
Takes a long time - slow transit of material through tract
Rumen capacity limits feed intake - large volume = heavy and takes up space
Only small particles can pass to omasum
Lower digestibility = slower passage rate
How does rumination occur?
Regurgitation of digesta from reticulum
Reticulum contraction just before 1 degree, or 2 degree contraction cycle
relaxation of esophageal sphincter
Reverse peristalsis of esophagus
tongue squeezes out liquid
mastication & salivation
What causes a decreased motility of the rumen?
Direct depression of gastric center - medications, acute phase proteins, pain
failure or neuromuscular transmission
increased sympathetic stimulation
What does buffering do to the rumen? how is it buffered?
Acids constantly being produced during fermentation - buffering keeps pH relatively close to neutral
saliva has large amounts of HCO3- and phosphate buffers
Carbonic anhydrase - enzyme in rumen epithelium, H+ absorbed into blood, HCO3- stays in rumen as a buffer
What is solid turnover?
Rate of loss of solid material
factors include - feed digestibility, feed intake, particle size
What are the 3 types of ruminants? aspects?
Browsers - high quality plant material, higher concentrate diet, more frequent meals = deer
Grazers - eat most plant material, higher fiber, less frequent meals = cattle and sheep
Intermediate
How is motility controlled?
No autonomous smooth muscle contractions
Intrinsic nerve plexi - does not produce motility contractions, small variations in smooth muscle tone
Extrinsic control - autonomic nervous system
Vagal never is required for rumen motility
splanchnic nerve - sympathetic
Controlled by the gastric centers of the medulla
What are rumen characteristics?
Temperature and pH
Aspects of saliva in ruminant digestion?
Modifies rumen pH through buffering
nutrients for microbes - nitrogen recycling
Anti-frothing properties - reduces surface tension
Enzymes - pre gastric esterase (fat digestion), and no salivary amylase
What is the turnover and efficiency of the rumen?
More turnover = more substrate for bacteria - increases VFA production
Increased microbial efficiency
Potential reasons - favours faster-growing bacteria, more bacteria in exponential growth phase, increase dilution rate = decrease protozoa to eat bacteria