GI physiology 4: ruminants & hindgut fermenters

What are the 2 ways to break down food?

digestive and fermentative

digestive breakdown

digestive enzymes

fermentative breakdown

microbial symbiosis

What microbes are included in the rumen ecosystem?

• protozoa

• virus

• bacteria

• fungi archaea

What does the rumen act as?

complex microbial ecosystem facilitating fermentation of plant material

What does microbial fermentation is the rumen unlock?

crucial nutrients and energy sources for the ruminant

What does VFA stand for?

volatile fatty acids

What is the main process of fermentation?

anaerobic bacteria ferment carbohydrates in plant material into short chain fatty acids

What carbohydrates do anaerobic bacteria ferment?

• cellulose

• hemicellulose

• starch

What are products of fermentation?

• short chain fatty acids

• methane gas

• ammonia

• B vitamins

Where are short chain fatty acids from fermentation absorbed?

through rumen wall

What provide the main energy source for ruminants?

short chain fatty acids

What do ruminal microbes utilise to synthesise their own protein?

ammonia produced by rumen bacteria

What do ruminal microbes utilise ammonia for?

synthesise own protein

Where do ruminants get proteins from?

microbes when they’re flushed through

Rumen

largest and most important chamber, houses the microbial ecosystem and performs majority of fermentation

Reticulum

has muscular walls that contract and relax, mixing rumen contents and aiding regurgitation for chewing

Omasum

• absorbs water and electrolytes

• further breaks down feed particles

• sorts material for passage to abomasum

Abomasum

• true stomach

• glandular lining similar to monogastric animals

• secretes digestive enzymes acids to digest protein and prepare digesta for further absorption in the SI

What techniques are used to study the motor patterns in ruminants?

• endoscopy

• balloon manometry

• electro-myography

• cine-radiography

Why is the motor pattern in ruminants studied extensively?

commercial pressure to understand ruminant

What is the rumen critically dependent on?

ANS - especially vagus nerve

What is the shaded area in the dorsal sac and dorsal blind sac?

gas cap

What are the thin dotted lines?

pillars of the rumen

What does the heavy line in each tracing indicate?

actively contracting portion of wall

Why is the gas cap clinically significant?

risk of bloat if not removed

What are these images?

tracings from radiographs

What are the 2 types of contractions of the rumen?

primary and secondary

How frequent are primary contractions (of rumen)?

1-1.5/min in cattle (>in sheep)

What happens to primary contractions if the ruminant is fed more food?

stronger contraction

What is the primary purpose of primary contractions (of rumen)?

mixing

What does the strength of primary contractions (of rumen) correlate with?

rumen fill

Under what circumstances are primary contractions (of rumen) absent?

deep sleep and/or illness

Where do primary contractions begin?

reticulum and sweeps aborally (peristaltic)

What pattern of movement do primary contractions (of rumen) have?

figure of 8 (sweeps fibrous mat from front to back and sets up figure of 8 pattern of movement)

How frequent are secondary contractions (of rumen)?

about half primary contractions followed by secondary contraction

When are primary and secondary contractions (of rumen) 1:1?

high fermentation rate

What is the primary purpose of secondary contractions (of rumen)?

moves gas cap forwards to clear cardia and allow eructation of gas

Are secondary contractions (of rumen) strong or weak?

relatively weak

Where do secondary contractions (of rumen) begin?

caudal sac and moves forwards (anti-peristaltic)

What is motility reduced by?

stress and pain

What does cutting the vagus nerve in a ruminant do?

abolished coordinated reticuloruminal motility

What is rumination a key diagnostic indicator of?

well-being

In a ruminant, when does chewing occur?

during eating (mastication) and rumination

What dictates the ratio of eating to rumination?

diet

Why is mastication & rumination time consuming?

• ruminants consume large mass of plant material per day

• plant material hard/tough

Why does eating time decrease with increased crude fibre in diet?

• higher CF → slower fermentation

• longer retention → reduced drive to eat

What effect does feeding rate have on digestibility?

increased feeding rate reduces ‘apparent digestibility’

Why does increased feeding rate reduce ‘apparent digestibility’?

• as feeding rate increases, time spent in gut reduces

• less rumination

• less fermentation

• less of the energy in food is released

In what food is it more pronounced that increased feeding rate reduces ‘apparent digestibility’?

food that’s harder to digest (e.g. late cut ‘coarse’ grass)

Eructation

voiding of gas from stomach

What gases does fermentation liberate?

CO₂ and methane

How many litres/min of CO₂ and methane does fermentation liberate in cattle?

1-2 litres per minute

What is the stimulus of the eructation reflex?

distension rumen

What reflex arc is involved in the eructation reflex?

vago-vagal reflex arc

What effect does the eructation reflex have?

stimulation of secondary ruminal wave

What does failure of the eructation reflex mechanism cause?

bloat or ‘ruminal tympony’

What are causes of bloat?

• oesophageal block

• foamy gas

• liquid covering cardia

• inhibition of secondary contraction of rumen

What is the composition of the gas that is voided from the stomach during eructation?

• CO₂ = 60%

• CH₄ = 40%

What are the steps of eructation?

• secondary ruminal wave

• oesophagus fills

• rapid antiperistalsis

• voided through nares

What percentage of eructated gas is inhaled by cows?

50%

What can cows inhaling 50% of eructated gas lead to?

milk taint

What are the 2 types of carbohydrates digested?

• alpha-bonded - starch

• beta-bonded - cellulose

What type of carbohydrate makes up the bulk of plant carbohydrate?

beta-bonded ‘structural carbohydrate’

Name examples of beta-bonded ‘structural carbohydrates’ found in plants?

• cellulose

• hemicellulose

• pectin

What do anaerobic microbes hydrolyse beta-bonds by?

fermentation

Can mammalian enzymes hydrolyse beta-bonds?

NO

What is glucose found as in tissues?

• CO₂

• glycogen

• fatty acids

• triacylglycerol

What tissues is CO₂ found in?

muscles, etc

What tissues is glycogen found in?

liver, muscle

What tissues are triacylglycerols found in?

liver, fat

What are examples of short chain fatty acids (VFA) in blood?

• acetate

• propionate

• butyrate

• ketone bodies

What is acetate converted into in tissues?

• triacylglycerol

• CO₂

What process is propionate converted into glucose and glycogen via?

gluconeogenesis

What is propionate converted into to be found as in tissues?

• glucose

• glycogen

What are butyrate and ketone bodies found as in tissues?

• triacylglycerol

• CO₂

How many carbons does acetate have?

2

How many carbons does propionate have?

3

How many carbons does butyrate have?

4

What 3 factors influence fermentation?

• substrates

• microbes

• conditions

What substrates influence fermentation?

• carbohydrates

• lipids

• proteins

What microbes (bacteria, protozoa & fungi) influence fermentation?

• substrate preferences

• tolerance to conditions

What are the conditions that influence fermentation?

• pH

• substrate concentrations

Are beta-linked carbohydrates soluble or insoluble in rumen fluid?

insoluble

Are starches soluble or insoluble in rumen fluid?

soluble

What are starches found highly in?

cereals

What are starches found low in?

grasses

What is the pH of the rumen?

5.5-7

How can changes in diet alter conditions for fermentation?

• alters substrates

• change in balance of microbes

• alters end products, substrates, pH, etc

What does relative abundance of bacteria reflect? (conditions for fermentation)

rate of growth/division

What can change the stability of the complex network of inter-dependency with & ratios of bacteria and protozoa?

food type

What does this equation show?

methanogenesis

In the USA, what are antibiotics against methogenic bacteria used for?

reduce loss via methane in beef production

What does the blue represent?

butyrate

What does the green represent?

propionate

What does the orange represent?

acetate

What kind of diet is 1?

high fibre diet

What kind of diet is 2?

high starch diet

What is ammonia produced during?

breakdown of amino acids (from dietary protein and fermentation of urea)

What is ammonia produced by?

rumen bacteria