Transcript Slide 1

Variation in the Susceptibility
to Ruminal Acidosis
G.B. Penner
Department of Animal and Poultry Science
University of Saskatchewan
Email: [email protected]
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Prevalence rates of SARA in dairy cows
• 12-30% prevalence across lactation
– Diagnosed using ruminocentesis
35.0%
30.0%
n = 662
25.0%
20.0%
15.0%
10.0%
5.0%
0.0%
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Krause and Oetzel, 2006
Acute ruminal
acidosis
pH 5.0
pH 5.5
Epithelial damage
Decreased fibre digestibility
Changes in rumen bacteria
Increased VFA
pH 6.0
Increased lactic
acid
SARA
Healthy
rumen
conditions
Consequences of ruminal acidosis
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How much variation do we see?
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Variation in the Severity of Ruminal
Acidosis
Duration below pH 5.8, h/d
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Minimum
Average
Maximum
20
16
12
8
4
0
Day 0-5
Day 17-19
Day 37-39
Day relative to parturition
Day 58-60
Penner et al., 2007
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Variation in ruminal acidosis around
parturition
Fairfield et al., 20076
Is the Response to acidosis consistent?
Salivary
buffer
Absorption
Passage
7
20
18
16
14
12
10
8
6
4
2
0
10
9
8
7
6
5
4
3
2
1
0
DMI
Duration <5.8
-5
5
17
37
Day relative to parturition
Duration pH < 5.8, h/d
DMI, kg/d
Severity is not entirely related to DMI
58
8
Penner et al., 2007
Resistant vs. susceptible heifers
Control
Resistant
Susceptible
3.0
6.9
6.7
2.0
6.5
1.5
6.3
1.0
6.1
0.5
5.9
0.0
5.7
-0.5
100% Hay
60% Hay
40% Hay
25% Hay
Diet
15% Hay
8% Hay
Mean rumen pH
Starch intake, kg/d
2.5
5.5
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Penner et al., unpublished
Subacute Ruminal Acidosis
Acid
production
Acid
removal
•Neutralization
•Clearance
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Acid Production in the Rumen
Many glucose molecules
++
2 acetate+ 2H
2H
2 propionate
+ +
+ 2H
2H
ACID
1 Glucose
pH
2 Pyruvate
1 butyrate + 1H
1H++
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Acid Removal from the Rumen
bicarbonate
blood
Saliva
H-SCFA
SCFAAcid
pH
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Physiological
for variation
Variation in
in
Physiological Causes
causes for
the Susceptibility
susceptibility to
to Ruminal
ruminal acidosis
the
Acidosis
Acid removal from the rumen
blood
Passage
Salivary
15.5%
buffer
Bicarbonate
28.0%
Absorption
Other
3.6%
Passage
Absorption
52.9%
Allen, 1997
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Regulating ruminal pH
Acid
Production
•Salivary
buffer
Acid
•Absorption
Removal
•Passage
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Relationship between saliva production
and ruminal pH
Duration pH <5.8, h/d
25.00
Duration pH <5.8 = 0.07 × saliva production – 4.7
P < 0.001
20.00
15.00
10.00
5.00
0.00
150.00
200.00
250.00
300.00
350.00
400.00
Total saliva production, L/d
Bowman et al., 2003; Yang et al.,152003
Regulating ruminal pH
Acid
Production
•Salivary
buffer
Acid
•Absorption
Removal
•Passage
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Rumen pH
~5.0 to 7.0
Intracellular pH
~7.4
% in dissociated state
Mechanisms: passive diffusion
100
90
80
70
60
50
40
30
20
10
0
1
2
3
4
5
6
7
8
9 10
pH
H-SCFA
H+
SCFAHCO3H2O + CO2
Carbonic anhydrase
Ruminal contents
Blood
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SCFA absorption and H+ removal
2K+
Na+
Na+/K+ ATPase
3Na+
H+
H+
KetonesLactate-
H-SCFA
H+
Metabolism
SCFAHCO3-
SCFA-
Apical surface pH > 7.4
H2O + CO2
Ruminal contents
Leonhard-Marek et al., 2006
Blood
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SCFA absorption and H+ removal
Na+
H+
Na+
H+
H+
2K+
3Na+
KetonesLactate-
H-SCFA
H+
Metabolism
SCFAHCO3-
SCFA-
H2O + CO2
Ruminal contents
Blood
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Mechanisms of SCFA absorption
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Acetate uptake, nmol/(mg protein × min)
Mechanisms: protein mediated
5.0
4.5
4.0
P < 0.001
a
3.5
3.0
2.5
b
2.0
1.5
b
1.0
0.5
0.0
Bicarbonate buffer
Bicarbonate-free
buffer
Bicarbonate free
buffer + nitrate
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Penner et al., 2009
Acetate vs. butyrate
Protein mediated
40-72%
Uptake, nmol/(mg protein × min)
4.5
12.0
Passive diffusion
31-72%
4.0
10.0
3.5
3.0
2.5
Passive diffusion
28 – 60%
8.0
6.0
2.0
1.5
Protein mediated
28-69%
4.0
1.0
2.0
0.5
0.0
0.0
Bicarbonate Bicarbonate Bicarbonate
dependent independent independent
nitrate
nitrate
sensitve
insensitive
Bicarbonate
dependent
Bicarbonate
independent
nitrate
sensitve
Bicarbonate
independent
nitrate
insensitive
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Penner et al., 2009
SCFA absorption and H+ removal
Na+
Aschenbach et al., 2010
H+
Na+
H+
H+
2K+
3Na+
H+
KetonesLactate-
H-SCFA
H+
Metabolism
SCFAHCO3-
HCO3-
SCFAHCO3-
H2O + CO2
Ruminal contents
Blood
Na+
HCO3-
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SCFA absorption and ruminal pH
• Appearance of bicarbonate in luminal buffer
Buffer pH
(Ash and Dobson, 1963; Gäbel et al., 1991)
9
8
7
6
5
4
3
2
1
0
Initial
1
Final
2
3
Buffer
4
Dijkstra et al., 1993
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Variation in ruminal pH
7.0
Duration pH < 5.8, h/180 min
180
6.2
5.8
5.4
a
P < 0.05
160
140
120
100
b
80
Control
60
40
Resistant
c
20
Susceptible
0
Control
Resistant
Susceptible
0
-360
-720
-1080
-1440
-1800
-2160
-2520
5.0
-2880
Ruminal pH
6.6
Time relative to the challenge, min
Penner et al., 2009
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Uptake, nmol/cm2/h
SCFA absorption explains variation in
ruminal pH
16
Control
14
Resistant
12
Susceptible
P <0.05
10
b
b
a
8
6
a
b
b
4
2
0
Acetate
Butyrate
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Mechanism of acetate uptake and
ruminal pH
Penner et al., 2009
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Mechanism of butyrate uptake and
ruminal pH
•Non-responders
also had higher
serum butyrate
Penner et al., 2009
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SCFA absorption and ruminal pH
Resende Júnior et al., 2006
r2 = 0.43
P <0.001
r2 = 0.45
P <0.001
Gene
Acyl-CoA synthetase
HMGCL
LDHb
PC
r2 = 0.17
P <0.001
Pathway
R
P value
Activation of SCFA
-0.92
0.01
Ketogenesis
-0.75
0.08
Lactate metabolism
-0.84
0.03
Pyruvate metabolism
0.88
0.02
Penner et al., 2009
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Take home messages
• Considerable variation among cows for the
susceptibility to ruminal acidosis
• Variation in susceptibility is related to
differences in the total absorption and
pathway of absorption for SCFA
• Future research is required to determine the
molecular regulation for acidosis susceptibility
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Thank You!
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