digestive physiology of the ruminant

Question 1

concentrate selectors

Answer 1

very selective
limited fibre digestion
high feeding rhythm

Question 2

intermediate feeders

Answer 2

adaptive mixed feeders

Question 3

roughage grazers

Answer 3

nonselective grazers
good ability to digest fibre
low feeding rhythm

Question 4

chewing

Answer 4

chew in the lateral (grinding) motion on one side of mouth at a time
needed to increase surface area of feeding particles
feeding chewed primarily during rumination in grazing species

Question 5

mouth- teeth

Answer 5

function: reduce particle size
anatomy: upper dental pad
lower incisors
premolars
molars

Question 6

saliva

Answer 6

from at least three paired glands:
submaxillary, sublingual, parotid
7 litres/d sheep
150 litres/d cow
aids in mastication, swallowing, forming bolus:
no digestive enzymes in the saliva of mature ruminants, provides N, P, S and Na for rumen microorganisms, contains HCO3 and (PO4)-3: buffering compounds to maintain rumen pH

Question 7

oesophagus

Answer 7

involved in rumination
different from mono gastric oesophagus: striated muscle along the entire length, provides greater strength, allows some voluntary control.
funnel shaped at the bottom.

Question 8

ruminant stomach

Answer 8

anatomy:
reticulum
rumen
omasum 
abomasum

Question 9

reticuloruminal motility

Answer 9

occurs early life- persists for the lifetime of the animal
one to two cycles per minute
function:
mixes the ingesta
aid in eructation go gas
force fluid and fermented foodstuffs into the omasum

Question 10

rumen contractions

Answer 10

inoculate incoming feed with microbes
mix contents: minimise effects of stratification, move fermentation products to rumen wall
particle sorting and passage of small particles to omasum
rumination
eructation of fermentation gases

Question 11

belching bovine

Answer 11

eructation: burping
fermentation= gas production
CO2 (65%), CH4 (25%), N2 (7%), O2, NH3, H2, H2S
expelled by upper sacs of rumen

Question 12

reticulum

Answer 12

honeycomb lining: no secretions
formation of food bolus
regurgitation initiated here
collects hardware (nails, wire)

Question 13

four steps of rumination

Answer 13

regurgitation: reverse peristalsis carries food to mouth
remastication: liquid squeezed from bolus and swallowed, bolus chewed
reinsalivation: adding more saliva
redeglutition: swallowing bolus and liquids

Question 14

rumination

Answer 14

allows animal to forage and eat food rapidly, and then store for later digestion.
reduces particle size: only small particles leave reticulo-rumen.
increase surface area for microbial attachment and digestion/fermentation
additional saliva- further buffering in the rumen.

Question 15

rumen

Answer 15

digestion and fermentation chamber: cow 80-125 litres, no secretions.
contains anaerobic microbes (25-50 billion bacteria/ml fluid): also protozoa, fungi.
microbial fermentation produces volatile fatty acids (VFA).
papillae lining: increase surface area, absorption of VFA.

Question 16

volatile fatty acids

Answer 16

acetic acid: is utilised minimally in the liver, and is oxidised throughout most of the body to generate ATP.
propionic acid: is almost completely removed from the portal blood by the liver, within the liver, propionate is major substrate for gluconeogenesis- glucose generation.
butyric acid: is oxidised in many tissues for energy production.

Question 17

omasum

Answer 17

laminae lining: muscular folds, no secretions.
reduces particle size.
absorption of water: -60% removed.
absorption of VFAs.
absorption of bicarbonate ions: prevents buffering of the abomasum.

Question 18

young animals

Answer 18

the reticulum, rumen and omasum in young animals are relatively under-developed.
depends on the esophageal groove- reticulorumen muscular fold stimulated by sucking, anticipation and milk proteins.

Question 19

abomasum, small intestine and large intestine

Answer 19

similar in structure and function in monogastric.

limited ability to digest starch.

Question 20

abomasum

Answer 20

true gastric stomach- 18 litres in a cow: three regions (cardiac, fundic and pyloric), digestive secretions.
pH decreases from 6 to 2.5: denatures proteins; kills rumen micro-organisms, dissolves minerals.

Question 21

small intestine

Answer 21

duodenum: 2.7-4; receive pancreatic juices, enzymes, flow rate regulation.
jejunum: 4-7; enzymes, absorption.
ileum: 7-8; absorption.

Question 22

large intestine

Answer 22

second site of fermentation: bacteria similar to rumen, but little protozoa.
digestion in the caecum and colon may account for as much as: 27% of cellulose digestion, 40% of hemicellulose digestion, 10% of starch digestion.
absorption of ammonia-N.
mineral absorption.
water absorption: 90% of water entering the LI is absorbed.