Anatomy of the Anatomy of the Ruminant StomachRuminant Stomach

• Extensive pre-gastric Extensive pre-gastric microbial fermentationmicrobial fermentation

• 4 compartments 4 compartments

Cow rumen

Cow reticulum

The inside of the omasum

Reticular epithelium

The interior surface of the rumen

Lining or epethelia Lining or epethelia of the reticulo-of the reticulo-

rumenrumen

cattle (left), sheep cattle (left), sheep (right)(right)

• Papillae most dense in Papillae most dense in the ventral sacthe ventral sac

• where most absorption where most absorption occursoccurs

Papillae Papillae developmentdevelopment

Fermentation/absorption driving factor

Reticular Reticular groove groove (pinned (pinned

in an open in an open position)position)

cardiacardia

reticuloreticulo-omasal -omasal orificeorifice

Reticular Reticular groove groove (in a (in a

closed closed position)position)

esophaguesophaguss

reticularreticular

groovegroove

OmasumOmasum

tightly packed with tightly packed with digesta (left)digesta (left)leaves or foldsleaves or folds

Cow omasum

Function of the Function of the OmasumOmasum

• acts as a filter to sort out acts as a filter to sort out liquid and particles for liquid and particles for passage to the abomasumpassage to the abomasum

• selective retention of the selective retention of the coarse particlescoarse particles

• absortive site for water, absortive site for water, VFA, Na, K, etcVFA, Na, K, etc

• reduction of the net reduction of the net volume entering the volume entering the abomasumabomasum

AbomasumAbomasum

fundic fundic folds folds (unique)(unique)

duodenumduodenum

pylorupyloruss

fundifundicc

Cow abomasum

Function of the Function of the AbomasumAbomasum

• digesta to abomasum digesta to abomasum continuouscontinuous

• thus, continuous secretion thus, continuous secretion of gastric juice (pepsin. of gastric juice (pepsin. HCl)HCl)

• stimulated by VFA and stimulated by VFA and lactic acidlactic acid

• short retention time (< 3 short retention time (< 3 h)h)

• digesta entering: pH 6.0digesta entering: pH 6.0• digesta leaving: pH 2-3digesta leaving: pH 2-3

MotilityMotility

• Mixing of digestaMixing of digesta• passage of digesta passage of digesta

through the reticular-through the reticular-omasal orificeomasal orifice

Rumen motilityRumen motility

• Contraction/relaxation of Contraction/relaxation of reticulo-rumenreticulo-rumen– moves and mixes digestamoves and mixes digesta– passage of digesta through the passage of digesta through the

reticular-omasal orificereticular-omasal orifice

• initial contraction of the initial contraction of the reticulumreticulum

• 2nd powerful contraction of 2nd powerful contraction of reticulumreticulum

• wave of contractions passing wave of contractions passing over rumenover rumen

• about 60 secsabout 60 secs

Contraction Contraction sequence sequence of RRof RR

Movement of Movement of DigestaDigesta

RuminationRumination

- “cud-chewing”- “cud-chewing”

- regurgitation of digesta- regurgitation of digesta

- re-swallowing of liquid - re-swallowing of liquid and fine particlesand fine particles

- mastication/ensalivation - mastication/ensalivation of bolus (40 - 70 sec)of bolus (40 - 70 sec)

- pause (2 - 6 sec)- pause (2 - 6 sec)

Eating and Eating and ruminatingruminating

• increases saliva secretionincreases saliva secretion• helps reduce particle size helps reduce particle size

of feedof feed• promotes passage of promotes passage of

digesta from the RR digesta from the RR which alleviates gut fillwhich alleviates gut fill

EructationEructationc.c. Rumen contraction forces gas Rumen contraction forces gas

to the back and then forwardto the back and then forward

d.d. Gas forced up esophagus to Gas forced up esophagus to the tracheathe trachea

GAS GAS

GAS

Esophageal Esophageal FistulaeFistulae

Rumination Rumination boluses (liquid)boluses (liquid)

upup downdown

Rumination Rumination boluses (dry)boluses (dry)

upup downdown

Role of Role of ruminationrumination

• saliva saliva secretion secretion – 2-4 x higher 2-4 x higher

than during than during restingresting

• particle size particle size reductionreduction

Chewing activity of dairy Chewing activity of dairy cowscows

00

22

44

66

88

1010

1010 1515 2020 2525 3030 3535 4040

NDF-f (% DMI)NDF-f (% DMI)

EatingEating RuminatingRuminating

alfalfa hayalfalfa hay

alfalfa hayalfalfa hay

orchardgrassorchardgrass

corn silagecorn silage

1010 1515 2020 2525 3030 3535 4040

h/d

h/d

Ruminating, h/dRuminating, h/d

Total chewing, h/dTotal chewing, h/d

Diets contained 5% forage (DM basis)Diets contained 5% forage (DM basis)Ruminating, h/dRuminating, h/d 4.4 4.4 5.55.5

Total chewing, h/dTotal chewing, h/d 7.3 7.3 7.97.9

9.49.4

16.116.1

CoarseCoarse 8686

MediumMedium 8181

MediumMediumfine fine 7575

FineFine 6969

Rumination by feedlot cattleRumination by feedlot cattle

Diets contained 10% silage Diets contained 10% silage (DM basis)(DM basis)

9.39.3

15.815.8

8.18.1

13.613.6

6.86.8

13.313.3

SilageSilage StrawStraw

SalivationSalivation

• lubrication of feed for lubrication of feed for swallowingswallowing

• passage of feed through the passage of feed through the GI tractGI tract

• buffers (bicarbonate, buffers (bicarbonate, phosphate) acids produced phosphate) acids produced during digestionduring digestion

• enzymic activityenzymic activity– no amylase in ruminantsno amylase in ruminants– pregastric esterase or lipase pregastric esterase or lipase

(preruminant)(preruminant)• nutrients for microbes: mucin, nutrients for microbes: mucin,

P Mg, ClP Mg, Cl

• anti-frothing propertiesanti-frothing properties (bloat)(bloat)

Salivary glands

Parotid saliva: ~ 50 % of total saliva

Amount of SalivaAmount of Saliva

• parotid cannulationparotid cannulation– total collection of salivatotal collection of saliva– only one ductonly one duct

• re-entrant parotid re-entrant parotid cannulationcannulation

• collection at the cardia collection at the cardia using a bagusing a bag– requires partial rumen requires partial rumen

emptyingemptying

SheepSheep

Do animals that eat more Do animals that eat more slowly produce more saliva slowly produce more saliva ??

VFAVFA

Rumen pHRumen pH

particle particle lengthlength

feed digestion

VFA product

ion

saliva

chewingchewing

Effects of level of fiber in the diet Effects of level of fiber in the diet on ruminal pH of dairy cowson ruminal pH of dairy cows