Lecture 10 - Ruminant Physiology Flashcards
3 modes of motility of the reticulo-rumen
- mixing
- eructation = burping, getting rid of gas that is a product of fermentation
- rumination = bringing up cud to rechew
The rumen doesn’t have villi, what does it have?
- Papillae
Rumen papillae
- 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
What is the rumen a large compartment for? (main fxn)
microbial fermentation
Where are rumen papillae found?
- ventral part of rumen
What are the 2 sensory receptors found in the rumen?
- Tension receptors: excited by passive distention
- Epithelial receptors: excited by physical and chemical stimuli
What kind of the environment is the rumen?
moist and warm; suitable for fermentation
What is the pH of the rumen?
- 5.5 to 7.1 (fairly neutral)
- buffered (able to keep this pH) due to saliva
Why does eructation need to occur?
- when microbes ferment they produce gas (ex. methane, CO2)
What happens to fermentation end products?
They are absorbed
- SCFA = acetate, propionate, butyrate
- papillae increase SA for absorption
Reticulum (“tripe”)
- 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
What does contraction of the reticulum facilitate?
- regurgitation for rumination
- mixing digesta in the reticuluo-rumen
- passage of digesta to the omasum
What is the purpose of the reticular groove?
- 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
Omasum
- 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
Main fxn of omasum
absorption of water and VFA
Abomasum
- true stomach secreting hydrochloric acid and enzymes
- mucosal epithelial cells
Steps for mixing (via contractions) of the reticulo-rumen
- starts with double (biphasic) contraction in reticulum
- anterior dorsal sac of rumen
- caudal region of rumen
- main ventral rumen
- caudoventral sac
What does rumen contraction enhance? Why?
- VFA absorption
- after mixing digesta, VFA are redistributed evenly close to papillae absorptive surface
4 rumen content layers
- Gas Layer
- Fiber Mat (intense fermentation)
- Intermediate Zone (intense fermentation)
- Liquid zone (moderate fermentation)
Eructation of the reticulo-rumen
- 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) - 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
What side do we puncture for bloat?
LEFT
Rumination of reticulo-rumen
- coordinated series of events involves respiratory muscles, larynx, pharynx, esophagus, buccal apparatus, and reticulum
What happens during the additional reticular contraction preceding biphasic contraction?
- 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
How many rumination periods occur within 24 hours?
- evenly distributed up to 14 periods/24h
What influences time of rumination?
- Cattle on hay: 8hr/d
- Cattle on concentrates: 2.5/d
- Long vs chopped hay: short = less rumination = less buffering = risk of acidosis
Rank the fermentability of sugar, starch and fiber
sugar > starch > fiber
What does excess ruminal fermentation result in?
- greater fermentation acid production (VFA and lactate)
Rumination stimulates saliva secretion which is good why?
saliva contains buffer and helps maintain stable ruminal environment
What is ruminal pH determined by?
- the balance btw VFA production and buffering capacity of rumen (saliva secretion)
What CHOs get fermented? What are the products?
Fermented: starch, fiber, sugar, pectin
Products: acetate, propionate, butyrate, CO2, CH4
How is the composition and abundance of VFA affected by diet?
- 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)
Why is propionate the most energetically efficient SCFA?
- not losing CO2 in the process
What happens if you change from a forage to concentrate diet?
- increase in propionate initially but it can start to drop off and you get a big increase in lactate
- low pH = risk of acidosis
Metabolic fate of acetate
- energy source in most tissues
- substrate for FA synthesis in adipose tissues and mammary gland
- not used for glucose synthesis
Metabolic fate of propionate
- primarily taken up by the liver to produce glucose
Metabolic fate of butyrate
- 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
What does poor quality hay result in?
- slows down rumen emptying into the omasum
- affects overall digestibility
