Carbohydrate digestion and metabolism in Ruminants Carbohydrate Digestion & Metabolism in Ruminants

Topic:-Carbohydrate Digestion &
Metabolism in Ruminants
Animal Nutrition Research Station,
College of Veterinary Science &A.H. Anand
Dr. Rahul Kumar Dangi

OVERVIEW OF DIGESTIVE TRACT OF RUMINANT 2
Dr. Rahul Dangi

Ruminant carbohydrate digestion
• • Mouth
• Salivary amylase
a. Breaks starches down to maltose
b. Plays only a small role in breakdown because of the short
time food is in the mouth
c. Ruminants do not have this enzyme
d. Not all monogastrics secrete it in saliva
3
Dr. Rahul Dangi

COMPARTMENTS OF STOMACH IN RUMINANTS
RUMEN RETICULUM OMASUM ABOMASUM
4
Dr. Rahul Dangi

Rumen
• The rumen is the largest stomach compartment and consists
of several sacs.
• In ruminants major part of microbial fermentation takes place
in the rumen.
• Rumen containing number of papillae which are of different
size and shapes which are the main organ of absorption.
• In all ruminants the papillae are most numerous and longest in
cranial sac followed by the caudo-dorsal blind sac.
• Papillaes provides more absorptive surface.
5
Dr. Rahul Dangi

Ruminant carbohydrate digestion
• Dietary carbohydrates are primarily from the plants and are fiber,
sugars and starches.
• Plant fibers are not digested by hydrolytic digestion but by
microbial digestion, while sugars and starches are digested by
hydrolytic digestion with the help of mammalian enzymes.
• Ingested carbohydrates are exposed to extensive pregastric
fermentation
• Most carbohydrates fermented by microbes
• Rumen fermentation is highly efficient considering the feedstuffs
ingested
6
Dr. Rahul Dangi

Reticulorumen
• • Almost all carbohydrate is fermented in the rumen
I. Some 'bypass' starch may escape to the small
intestine
II. No salivary amylase, but have plenty of pancreatic
amylase to digest starch.
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Dr. Rahul Dangi

FUNGI 103 /ML OF RUMEN
LIQUOR
---
BACTERIA 1010 /ML OF
RUMEN LIQUOR
----
PROTOZOA 106 /ML OF
RUMEN LIQUOR
Ruminal contents

Microbial Populations
• Amylolytic bacteria (starch, sugar
digesters)easyFreshworks
• Digest starches and sugars
• Prefer pH 5-6
• Produce propionate, butyrate and sometimes lactate
• Predominate in animals fed grain diets
• Rapid change to grain diet causes lactic acidosis (rapidly
decreases pH)
1) Streptococcus bovis
9
Dr. Rahul Dangi

Microbial metabolism
• ..
cata
boli
sm
bios
yant
hesi
s
sugar
s
VFAS
CO2
CH4
HEAT
11
Dr. Rahul Dangi

Metabolic
pathways of
major CHO
of plants to
3C
(pyruvate)
units in
rumen
12
Dr. Rahul Dangi

Metabolic
pathways
of
degradatio
n of 3C
units
(pyruvate)
to diferrent
VFAs

.
• In young ruminants, rumen and the reticulum are not fully developed
and are relatively small.
• The reticular/esophageal groove reflex, a tube-like fold of tissue,
channels milk or water that is sucked from a nipple directly through
the omasum to the abomasum.
• This is a reflex, stimulated by sucking. When the animal is weaned, it
normally loses this reflex.
• Solid food, such as creep feed, passes into the small rumen and
fermentation starts.
• The neonatal ruminant animal has no ruminal bacterial population
but from birth, it starts to pick up bacteria from the mother and
environment, particularly through contact.
• Solid food is then fermented forming VFAs, which stimulate the
growth and development of the rumen, particularly the growth of the
papillae for absorption.
14
Dr. Rahul Dangi

Carbohydrate Digestion in
Ruminants
• Carbohydrate digestion in ruminant animals is through
microbial fermentation in the rumen.
• Dietary carbohydrates are degraded (fermented) by rumen
microbes (bacteria, fungi, protozoa).
• The purpose of rumen fermentation is to produce energy as
ATP for the bacteria to use for protein synthesis and their
own growth.
• VFAs, also known as short-chain fatty acids, are produced as
a product of rumen fermentation and are absorbed through
the rumen wall and are utilized by the animal as an energy
source.
15
Dr. Rahul Dangi

The three major VFAs are acetic (C2), propionic (C3), and
butyric acid (C4)
16
Dr. Rahul Dangi

Proportion of VFA
• On predominantly hay diet = A-65%, P-20%, B-9%,
Branched chain FA- 5%, and n-valeric acid 1%.
• Total VFA conc. In rumen liquor varies between 2-15
g/litre.
• Total weight of acids produced may 4 kg per day.
17
Dr. Rahul Dangi

.
• Propionic acid formed primary from the decarboxylation
of succinate when fibrous carbohydrates are fermented.
High starch and sugar diet produces lactic acid.
• Lactic acid is stronger acid than VFAs but absorb slowly
than VFAs
18
Dr. Rahul Dangi

.
• All the digested and absorbed monosaccharides and volatile fatty
acids enter into the liver.
• The end products of rumen fermentation are microbial cell masses,
or microbial protein-synthesized VFA, and gases such as carbon
dioxide, methane, hydrogen, and hydrogen sulfide.
• The products of fermentation will vary with the relative
composition of the rumen microflora.
• The microbial population also depends on the diet, since this
changes the substrates for fermentation and subsequently the
products of fermentation.
• For example, starch is the major dietary constituent in concentrate-
fed ruminants (e.g., feedlot cattle)..
20
Dr. Rahul Dangi

.
• The rumen of such animals will have higher amylolytic bacteria than
cellulolytic bacteria present in the rumen of roughage- and pasture-fed
animals.
• Factors such as the forage:concentrate ratio, the physical form of the diet
(ground vs. pelleted), feed additives, and animal species can affect the rumen
fermentation process and VFA production.
•
Molar ratios of VFAs are dependent on the forage:concentrate ratio of the
diet. Cellulolytic bacteria tend to produce more acetate, while amylolytic
bacteria produce more propionic acid.
• Typically three major VFA molar ratios are 65:25:10 with a roughage diet and
50:40:10 with a concentrate-rich diet.
• Changes in VFA concentration can lead to several disorders of carbohydrate
digestion in ruminants.
• Rumen acidosis occurs when animals are fed high-grain-rich diets or when
animals are suddenly changed from pasture- or range-fed to feedlot
conditions
21
Dr. Rahul Dangi

Summary
1.Very little digestion occurs in the mouth in farm animals.
2.The small intestine is the site of carbohydrate digestion in monogastrics.
3.Pancreatic amylase acts on alpha 1,4 links, and other disaccharidases and
remove disaccharide units.
4.The end product (mainly glucose) diffuses into the brush-border using
ATP-dependent glucose transporters.
5.Undigested (fiber, nonstarch polysaccharides [NSP]) in the hindgut can
serve as an energy source for hindgut microbes in monogastrics.
6.Ruminant carbohydrate digestion is very different from monogastrics. First,
there is no amylase secreted in the saliva and then most carbs are
fermented in the rumen by microbial enzymes.
22
Dr. Rahul Dangi

.
7. Carbohydrates are fermented to volatile fatty acids (VFAs) in
the rumen. These include acetic acid, propionic acid, and
butyric acid.
8. VFAs are absorbed through the rumen wall into the portal
vein and are carried to the liver.
9. Ratios of the VFAs change with the type of diet. Roughage
diets favor microbes that produce more acetic acid, whereas
concentrate diets favor microbes that produce more
propionic acid.
10. Carbohydrate fermentation disorders in ruminants include
rumen acidosis (grain overload), when cattle are fed high-
starch-based cereal or grain-rich diets or when there is a
sudden change from pasture to feedlot.
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Dr. Rahul Dangi

CARBOHYDRATE
METABOLISM IN DAIRY
COWS
Dangi Rahul

TYPES OF CARBOHYDRATES FIBROUS
CARBOHYDRATES
FIBROUS CARBOHYDRATES
• Cellulose and hemicellulose bound with lignin in plant cell walls or fiber.
Provide bulk in the rumen. Fermented slowly.
• The lignin content of fiber increases with plant maturity and the extent of
cellulose and hemicellulose fermentation in the rumen decreases.
• Fiber in the form of long particles essential to stimulate rumination. Which
enhances the breakdown and fermentation of fiber and stimulates ruminal
contraction, and increases the flow of saliva to the rumen.
• Saliva contains sodium bicarbonate (baking soda) and phosphate salts which
help to maintain pH of the rumen close to neutral.
• Rations lacking fiber generally result in a low percentage of fat in the milk and
contribute to digestive disturbances (e.g., displaced abomasum, rumen
acidosis).
26
Dr. Rahul Dangi

NON-FIBROUS CARBOHYDRATES
• Non-fibrous carbohydrates (starches and simple sugars) fermented rapidly
almost completely in the rumen. Increase the energy density, improves the
energy supply and affect bacterial protein synthesis in the rumen.
• Non-fibrous carbohydrates do not stimulate rumination or saliva production
and, in excess, they may impede fiber fermentation.
• Balance between fibrous and non-fibrous carbohydrates is important in
feeding dairy cows for efficient milk production.
• In a lactating dairy cow, the rumen, the liver and the mammary gland are the
major organs involved in the metabolism of carbohydrates.
27
Dr. Rahul Dangi

CARBOHYDRATE METABOLISM
• VOLATILE FATTY ACID PRODUCTION IN THE RUMEN
During ruminal fermentation, the population of microorganisms (chiefly bacteria)
ferments the carbohydrates to produce energy, gases (methane - CH4 and carbon
dioxide - CO2), heat, and acids. Acetic acid (vinegar), propionic acid and butyric acid
are volatile fatty acids (VFA) and make up the majority (>95%) of the acids produced
in the rumen.
Also, the fermentation of amino acids produces some acids called iso-acids. The
energy and the iso-acids produced during fermentation are used by the bacteria to
grow (i.e., primarily to synthesize protein).
The CO2 and CH4 are eliminated through belching, and the energy of the CH4 is
lost. Unless heat is necessary to maintain body temperature, the heat produced during
fermentation is dissipated. The VFA, end products of microbial fermentation, are
absorbed through the rumen wall.
29
Dr. Rahul Dangi

.
 Volatile fatty acids produced by ruminal
fermentation Name Structure
Acetic CH3-COOH
Propionic CH3-CH2-COOH
Butyric CH3-CH2-CH2-COOH
30
Dr. Rahul Dangi

ABSORPTION OF VFAs
• Directly absorb from rumen, reticulum, omasum & large intestine
(from rumen is prompt)
• Elevated level of VAFs in portal blood is noted within 10 min.
after eating.
• In acidic pH absorption is fastest for butyrate than propionate &
acetic acid.
• absorption by simple diffusion.
32
Dr. Rahul Dangi

Acetic acid Metabolism
• The major volatile fatty acid present in blood and
absorbed as such.
• Utilized for energy and also a precursor of fatty acid
(Short chain fatty acid of milk fat).
• Never converted to glucose.
• 10 ATP are produced per mole of acetic acid.
33
Dr. Rahul Dangi

Propionic acid Metabolism
•Propionic acid, produced in rumen, Carried
out to the liver through blood Changed into
glucose in liver.
•17 ATP are produced per mole of propionic
acid.
35
Dr. Rahul Dangi

• Propionic acid AMP? 1 CoenzymeA Propionyl CoA
ADP/ATP Biotin Methyl ralonyl CoA Succinyl CoA
Mathyl oxaloacetate Phophoenol pyruvate Glu!ose
36
Dr. Rahul Dangi

.
• Most of the acetate and all the propionate are transported to
the liver, but the majority of butyrate is converted in the
rumen wall to a ketone body called β-hydroxybutyrate.
Ketones, are important sources of energy (fuel for
combustion) for most tissues in the body.
• Ketones come primarily from the butyrate produced in the
rumen, but in early lactation, they also come from the
mobilization of adipose tissue.
37
Dr. Rahul Dangi

GLUCOSE PRODUCTION IN THE LIVER
• Most of the propionate is converted to glucose by the liver. In addition, the liver can use
amino acids for glucose synthesis.
• This is an important process because there is normally no glucose absorbed from the
digestive tract and all the sugar found in the milk (about 900 g when a cow produce 20
kg of milk) must be produced by the liver.
• An exception arises when cows are fed large amounts of concentrates rich in starch or a
source of starch resistant to ruminal fermentation. Then, the starch that escaped
fermentation reaches the small intestine. The glucose formed during intestinal digestion
is absorbed, transported to the liver and contributes to the supply of glucose to the cow.
• Lactate is another possible source of glucose in the liver. Lactate is found in well
preserved silages, but lactate production in the rumen occurs when there is excess starch
in the diet. This is undesirable because the rumen environment become acidic, fiber
fermentation stops and in extreme cases the cow stops eating.
38
Dr. Rahul Dangi

LACTOSE AND FAT SYNTHESIS IN THE UDDER
• During lactation, the mammary gland has a great need for glucose used primarily for the
formation of lactose .
• The lactose synthesized in the udder closely associated with the amount of milk produced
per day. The concentration of lactose in milk is relatively constant and water is added to
maintain lactose concentration about 4.5%. Glucose is converted to glycerol which is used
as the "backbone" of milk fat synthesis.
• Acetate and β-hydroxybutyrate are used for the formation of the fatty acids that are attached
to glycerol to form milk fat.
• The mammary gland synthesizes saturated fatty acids (4 to 16 carbons short chain fatty
acids).
• About half of milk fat is synthesized in the mammary gland. The other half comes from the
lipids in the diet, including a small amount of unsaturated fatty acids with more than 18
carbons (long chain fatty acids).
• The energy required for the synthesis of fat and lactose in the udder comes from the
combustion of ketones, but acetate and glucose may also be used as energy sources in the
cells of many tissues.
40
Dr. Rahul Dangi

THE EFFECT OF DIET ON RUMEN FERMENTATION AND MILK YIELD
• The amount and ratio of VFA produced depends on the source of
carbohydrates in the diet . (65% acetic, 20% propionic and 15%
butyric when ration contains enough forages.)
• The supply of acetate used to maximize milk fat production, but
propionate produced may limit the milk produced due to limited
supply of glucose.
• The non-fibrous carbohydrates more VFA . Concentrate feeding
results in faster / more complete fermentation, increased propionate
% at the cost of acetate. Acetic acid drops below 40%, Propionic acid
increases to 40%.
41
Dr. Rahul Dangi

Butyric acid Metabolism
•It is absorbed as aceto acetic acid and b hydroxy butyric
acid in its passage across the ruminal and omasal walls.
•It is ketogenic in nature and utilized for synthesis of long
chain fatty acid of milk fat.
•25 ATP are produced per mole of butyric acid.
42
Dr. Rahul Dangi

THE EFFECT OF DIET ON RUMEN
FERMENTATION AND MILK YIELD
• Milk production may be increased but less fat synthesis
due to short supply of acetate but fat production
reduced, Less fat % in the milk.
• Excess propionate used for fatty tissue deposition rather
than milk synthesis and may lead to fat cows.
• Continued feeding may result in difficult calving and to
develop fatty liver or ketosis.
• On the other hand, not enough concentrate in the
ration limits energy intake, milk production and milk
protein production.
44
Dr. Rahul Dangi

Forage: Concentrate Ration
• In summary, changes in the proportion of forage
and concentrate in the diet has a profound effect on
the amount and the percentage of each VFA
produced in the rumen. In turn, the VFA strongly
influence.
• Milk production.
• Milk fat percentage.
• The efficiency of conversion of feed to milk.
• The relative value of a ration for milk production as
opposed to fattening.
45
Dr. Rahul Dangi

CITRIC ACID CYCLE
• The citric acid cycle, also known as the Krebs cycle or
tricarboxylic acid (TCA) cycle, is the second stage of cellular
respiration.
• This cycle is catalyzed by several enzymes and is named in
honor of the British scientist Hans Krebs who identified the
series of steps involved in the citric acid cycle.
• The usable energy found in the carbohydrates, proteins,
and fats we eat is released mainly through the citric acid
cycle.
• Although the citric acid cycle does not use oxygen directly, it
works only when oxygen is present.
46
Dr. Rahul Dangi

.
Dangi
Rahul
47
Dr. Rahul Dangi

.
• The second stage of cellular respiration is called the citric acid cycle. It is
also known as the Krebs cycle after Sir Hans Adolf Krebs who discovered
its steps.
• Enzymes play an important role in the citric acid cycle. Each step is
catalyzed by a very specific enzyme.
• In eukaryotes, the Krebs cycle uses a molecule of acetyl CoA to generate
1 ATP, 3 NADH, 1 FADH2, 2 CO2, and 3 H+.
• Two molecules of acetyl CoA are produced in glycolysis so the total
number of molecules produced in the citric acid cycle is doubled (2 ATP, 6
NADH, 2 FADH2, 4 CO2, and 6 H+).
• Both the NADH and FADH2 molecules made in the Krebs cycle are sent
to the electron transport chain, the last stage of cellular respiration.
48
Dr. Rahul Dangi

What is the Electron Transport Chain
• The electron transport chain (ETC) is a group of proteins and
organic molecules found in the inner membrane of mitochondria.
Each chain member transfers electrons in a series of oxidation-
reduction (redox) reactions to form a proton gradient that drives
ATP synthesis. The importance of ETC is that it is the primary
source of ATP production in the body.
• In eukaryotes, multiple copies of electron transport chain
components are located in the inner membrane of mitochondria. In
bacteria (prokaryotes), they occur in the plasma membrane.
49
Dr. Rahul Dangi

• The electron transport chain has two essential functions in the
cell:
1.Regeneration of electron carriers: reduced electron carriers
NADH and FADH2 pass their electrons to the chain, turning
them back into NAD+ and FAD. This function is vital because
the oxidized forms are reused in glycolysis and the citric acid
cycle (krebs cycle) during cellular respiration.
2.Generating proton gradient: the transport of electron through
the chain results in a gradient of a proton across the inner
membrane of mitochondria, later used in ATP synthesis.
50
Dr. Rahul Dangi

Electron transport chain
• The electron transport chain is a series of four protein
complexes that couple redox reactions, creating an
electrochemical gradient that leads to the creation of ATP in a
complete system named oxidative phosphorylation.
• ETC consists of four complexes:
I. NADH dehydrogenase (Complex I),
II. Succinate dehydrogenase (Complex II),
III. Cytochrome b and c1 (Complex III), and
IV. Cytochrome c oxidase (Complex IV).
51
Dr. Rahul Dangi

.
NADH dehydrogenase (Complex I),Succinate dehydrogenase (Complex II),Cytochrome b and c1 (Complex III), and
Cytochrome c oxidase (Complex IV). 52
Dr. Rahul Dangi

.
• Complex I is the first enzyme of the respiratory chain.
It oxidizes NADH, which is generated through the Krebs
cycle in the mitochondrial matrix, and uses the two
electrons to reduce ubiquinone to ubiquinol.
•Succinate dehydrogenase (Complex II) plays a dual role in
respiration by catalyzing the oxidation of succinate to
fumarate in the mitochondrial Krebs cycle and transferring
electrons from succinate to ubiquinone in the mitochondrial
electron transport chain (ETC).
• Both complex I and complex II transfer electrons to
ubiquinone, which in turn transfers the electrons to complex
III.
53
Dr. Rahul Dangi

.
The flow of electrons in aerobic respiration comes to a halt when molecular
oxygen serves as the final electron acceptor.
In complex III, protons are carried across the membrane by coenzyme Q,
which accepts protons from the matrix at complexes I or II and releases
them into the intermembrane space at complex III. Complexes I and III
each transfer four protons across the membrane per pair of electrons.
What happen when complex 3rd inhibited: The consequences of inhibiting
complex III include an increase in the production of ROS reactive oxygen
species (Balaban et al., 2005; Panduri et al., 2004) and a reduction in the
cellular levels of ATP
Complex IV, also known as cytochrome c oxidase, catalyzes the final step in
the mitochondrial electron transport chain and is one of the key regulators
of oxidative phosphorylation. The name cytochrome c oxidase comes from the
fact that Complex IV absorbs electrons from cytochrome c.
54
Dr. Rahul Dangi

•1 FADH2 (x 2 ATP) = 2 ATP
•1 NADH (x 3 ATP) = 3 ATP
•1 acetyl-CoA (x 12 ATP) = 12 ATP
•Total = 2 + 3 + 12 = 17 ATP
ENERGY YIELD
55
Dr. Rahul Dangi

-
ATP YIELD FROM 1 MOLE OF ACETIC ACID
.
.
Attributes ATP (+) ATP (-)
1 mole of acetate to 1 mole of acetyl-Co A ------- 2
from cell cytoplasm to it reaches
mitochondrial matrix in a complex with
carnitine ; acetyl Co-A enters in TCA cycle
and is oxidized
10 -------
Net gain of ATP per mole of acetate 8 ---------
56
Dr. Rahul Dangi

areas of focus
ATP YIELD FROM 1 MOLE OF PROPIONATE ACID
.
.
2 moles of propionate to 2 mole of
succinyl-Co A
------- 6
2 mole of succinyl-Co A to 2 moles of
malate
5 -------
2 moles of malate to 2 moles
phosphoenolpyruvate
5 2
2 moles phosphoenolpyruvate to 1 mole of
glucose
-------- 5
1 mole of glucose to CO2 AND H2O 30 OR 32 -------
TOTAL 40 OR 42 13
Net gain of ATP per mole of acetate 27 OR 29 --
57
Dr. Rahul Dangi

areas of focus
ATP YIELD FROM 1 MOLE OF BUTYRATE ACID
.
.
1mole of BUTYRATE to 1 mole of D3-
hydroxybutyrate
4 4.5
1 mole of D3-hydroxybutyrate to 2 moles
acetyl Co A
2.5 2
2 mole Of acety-CoA to CO2 AND H2O 20 -------
TOTAL 26.5 6.5
Net gain of ATP per mole of butyrate 20 --
58
Dr. Rahul Dangi

Carbohydrate digestion and metabolism in Ruminants Carbohydrate Digestion & Metabolism in Ruminants

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