Anatomy of the Ruminant
Stomach
• Extensive pre-gastric
microbial fermentation
• 4 compartments
Cow rumen
Cow reticulum
The interior surface of the
rumen
Reticular epithelium
The inside of the omasum
Lining or epethelia of
the reticulo-rumen
cattle (left), sheep (right)
• Papillae most dense in the
ventral sac
• where most absorption
occurs
Papillae development
Fermentation/absorption
driving factor
Reticular groove
(pinned in an open
position)
cardia
reticuloomasal
orifice
Reticular
groove (in a
closed position)
esophagus
reticular
groove
Omasum
tightly packed with digesta
(left)
leaves or folds
Cow omasum
Function of the
Omasum
• acts as a filter to sort out
liquid and particles for
passage to the abomasum
• selective retention of the
coarse particles
• absortive site for water, VFA,
Na, K, etc
• reduction of the net volume
entering the abomasum
Abomasum
duodenum
pylorus
fundic
fundic
folds
(unique)
Cow abomasum
Function of the
Abomasum
• digesta to abomasum
continuous
• thus, continuous secretion of
gastric juice (pepsin. HCl)
• stimulated by VFA and lactic
acid
• short retention time (< 3 h)
• digesta entering: pH 6.0
• digesta leaving: pH 2-3
Motility
• Mixing of digesta
• passage of digesta through
the reticular-omasal orifice
Rumen motility
• Contraction/relaxation of
reticulo-rumen
– moves and mixes digesta
– passage of digesta through the
reticular-omasal orifice
• initial contraction of the
reticulum
• 2nd powerful contraction of
reticulum
• wave of contractions passing
over rumen
• about 60 secs
Contraction
sequence of
RR
Movement of
Digesta
Rumination
- “cud-chewing”
- regurgitation of digesta
- re-swallowing of liquid and
fine particles
- mastication/ensalivation of
bolus (40 - 70 sec)
- pause (2 - 6 sec)
Eating and
ruminating
• increases saliva secretion
• helps reduce particle size of
feed
• promotes passage of digesta
from the RR which alleviates
gut fill
Eructation
c. Rumen contraction forces gas to
the back and then forward
d. Gas forced up esophagus to the
trachea
Esophageal Fistulae
Rumination boluses
(liquid)
up
down
Rumination boluses
(dry)
up
down
Role of rumination
• saliva
secretion
– 2-4 x
higher
than
during
resting
• particle
size
reduction
Chewing activity of dairy
cows
Eating
Ruminating
10
8
h/d
6
alfalfa hay
4
alfalfa hay
orchardgrass
corn silage
2
0
10
15
20
25
30
35
40 10
15
20
NDF-f (% DMI)
25
30
35
40
Rumination by feedlot cattle
Coarse
86
Medium
81
Medium
fine
75
Fine
69
8.1
13.6
6.8
13.3
Diets contained 10% silage
(DM basis)
Ruminating, h/d
9.4
Total chewing, h/d 16.1
9.3
15.8
Silage
Straw
Diets contained 5% forage (DM basis)
Ruminating, h/d
Total chewing, h/d
4.4
7.3
5.5
7.9
Salivation
• lubrication of feed for swallowing
• passage of feed through the GI
tract
• buffers (bicarbonate, phosphate)
acids produced during digestion
• enzymic activity
– no amylase in ruminants
– pregastric esterase or lipase
(preruminant)
• nutrients for microbes: mucin, P
Mg, Cl
• anti-frothing properties (bloat)
Salivary glands
Parotid saliva: ~ 50 % of total
saliva
Amount of Saliva
• parotid cannulation
– total collection of saliva
– only one duct
• re-entrant parotid
cannulation
• collection at the cardia using
a bag
– requires partial rumen
emptying
Sheep
Do animals that eat more
slowly produce more saliva ?
VFA
feed
digestion
VFA
product
ion
Rumen pH
saliva
chewing
particle
length
Effects of level of fiber in the diet
on ruminal pH of dairy cows