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Modelling State Transitions Aur´ elien Madouasse Background Milk Recording Data Somatic Cell Count State Transition State Definition State Transitions Data A Simple Model Model WinBUGS code Results Adding Complexity SCC Variation Model WinBUGS code Results Discussion Modelling State Transitions Example of a Multinomial Logit Model Applied to Somatic Cell Count in Dairy Cows Aur´ elien Madouasse 19 th April 2010
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Page 1: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Modelling State TransitionsExample of a Multinomial Logit Model Applied to Somatic

Cell Count in Dairy Cows

Aurelien Madouasse

19th April 2010

Page 2: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Outline

1 BackgroundMilk RecordingDataSomatic Cell Count

2 State TransitionState DefinitionState TransitionsData

3 A Simple ModelModelWinBUGS codeResults

4 Adding ComplexitySCC VariationModelWinBUGS codeResults

5 Discussion

Page 3: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Outline

1 BackgroundMilk RecordingDataSomatic Cell Count

2 State TransitionState DefinitionState TransitionsData

3 A Simple ModelModelWinBUGS codeResults

4 Adding ComplexitySCC VariationModelWinBUGS codeResults

5 Discussion

Page 4: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

What is Milk Recording?

Milk recording is the regular collection of a milk samplefrom all lactating cows of a dairy herd

What is measured:

Milk yield% butterfat, % protein, % lactoseSomatic cell count

Information collected

Date of birthDate of calvingParity

Page 5: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

What is Milk Recording?

Farmers pay for milk recording, in order to:

Adapt managementIdentify cows likely to have mastitisIdentify the best producers

The information is also used for

Genetic evaluationEpidemiologic studies

Page 6: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

DataInitial Dataset

The National Milk Records: main provider of milkrecording in England and Wales

All the data collected by the NMR between January 2004and December 2006 were purchased:

19,893,093 recordings1,247,427 cows5,714 herds

⇒ Big!!!

Page 7: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

DataData Selection

Aim: Obtain a homogeneous dataset and discard unreliabledata

Herds recording:

For the 3 complete yearsOn a monthly basisAt least 80 % of Holstein-Friesian cows

Milk samples collected on 2 consecutive milkings

Final dataset

8,211,988 recordings483,747 cows2,128 herds

⇒ Reasonably big!!!

Page 8: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

DataData Selection

Aim: Obtain a homogeneous dataset and discard unreliabledata

Herds recording:

For the 3 complete yearsOn a monthly basisAt least 80 % of Holstein-Friesian cows

Milk samples collected on 2 consecutive milkings

Final dataset

8,211,988 recordings483,747 cows2,128 herds

⇒ Reasonably big!!!

Page 9: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Somatic Cell CountRelation to mastitis

Mastitis

One of the biggest health problems in dairy herdsCan be clinical or subclinicalCauses an increase in milk somatic cell count (SCC)

Page 10: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Somatic Cell CountRelation to mastitis

Individual Somatic Cell Count

Threshold of 200,000 cells/mL used to categorise cows asInfected/Uninfected

Bulk Milk Somatic Cell Count

Reflects herd mastitis prevalencePenalty on milk price when it is too high

Aims of the study

Can we model the transition between Low/High SCC fromindividual cow information?

Can we predict BMSCC from the predicted transitions?

Page 11: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Outline

1 BackgroundMilk RecordingDataSomatic Cell Count

2 State TransitionState DefinitionState TransitionsData

3 A Simple ModelModelWinBUGS codeResults

4 Adding ComplexitySCC VariationModelWinBUGS codeResults

5 Discussion

Page 12: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionDefinition of the States

First

Low/High

Low/High

Low/High

Low/High

Low/High

Last

Low/High

Low/High

Low/High

Low/High

Low/High

Low/High

Dry

Dry

Low/High

First

Low

High

Dry

Low

High

Last

Low

High

Page 13: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionTransition Matrix

CurrentLow High Dry Last

Pre

viou

s Low π11 π12 π13 π14

High π21 π22 π23 π24

Dry π31 π32 π33 π34

First π41 π42 π43 π44

Page 14: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionTransition Matrix

CurrentLow High Dry Last

Pre

viou

s Low π11 π12 π13 π14

High π21 π22 π23 π24

Dry π31 π32 π33 0First π41 π42 0 0

Page 15: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

DataData Used for the Study

Training data

100 randomly selected herdsDataset 1: 6 consecutive test-days used for parameterestimation (70,382 lines)Dataset 2: 7th test-day for validation (11,895 lines)

Validation data (Dataset 3: 14,669 lines)

100 randomly selected herds1 test-day per herd

Page 16: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Outline

1 BackgroundMilk RecordingDataSomatic Cell Count

2 State TransitionState DefinitionState TransitionsData

3 A Simple ModelModelWinBUGS codeResults

4 Adding ComplexitySCC VariationModelWinBUGS codeResults

5 Discussion

Page 17: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionModel

Stateij ∼ Multinomial(πij)

ln(πij

π1j) =

4∑i ′=1

I [State i ′

i(j−1)]αi ′i

State i

Cow-recording j

Previous State i ′

Page 18: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionModel

Stateij ∼ Multinomial(πij)

ln(πij

π1j) =

4∑i ′=1

I [State i ′

i(j−1)]αi ′i

State i

Cow-recording j

Previous State i ′

Page 19: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionWinBUGS code

model {

for(i in 1:N) {

resp[i,1:4] ~ dmulti(pi[i,1:4],1)

for(m in 1:4){pi[i,m] <- p[i,m]/sum(p[i,])

}

Page 20: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionWinBUGS code

model {

for(i in 1:N) {

resp[i,1:4] ~ dmulti(pi[i,1:4],1)

for(m in 1:4){pi[i,m] <- p[i,m]/sum(p[i,])

}

Page 21: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionWinBUGS code

model {

for(i in 1:N) {

resp[i,1:4] ~ dmulti(pi[i,1:4],1)

for(m in 1:4){pi[i,m] <- p[i,m]/sum(p[i,])

}

Page 22: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionWinBUGS code

model {

for(i in 1:N) {

resp[i,1:4] ~ dmulti(pi[i,1:4],1)

for(m in 1:4){pi[i,m] <- p[i,m]/sum(p[i,])

}

Page 23: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionWinBUGS code

p[i,1] <- 1

# Code for 2

log(p[i,2]) <- beta[1, i] + beta[2, i] + beta[3, i] + beta[4, i]

beta[1, i] <- pstate[i, 1] * theta[1]

beta[2, i] <- pstate[i, 2] * theta[2]

beta[3, i] <- pstate[i, 3] * theta[3]

beta[4, i] <- pstate[i, 4] * theta[4]

# Code for 3

log(p[i,3]) <- beta[5, i]+beta[6, i]+ beta[7, i] + beta[8, i]

beta[5, i] <- pstate[i, 1] * theta[5]

beta[6, i] <- pstate[i, 2] * theta[6]

beta[7, i] <- pstate[i, 3] * theta[7]

beta[8, i] <- pstate[i, 4] * gamma

Page 24: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionWinBUGS code

# Code for 4

log(p[i,4]) <- beta[9, i]+ beta[10, i] + beta[11, i] +

beta[12, i]

beta[9, i] <- pstate[i, 1] * theta[8]

beta[10, i] <- pstate[i, 2] * theta[9]

beta[11, i] <- pstate[i, 3] * gamma

beta[12, i] <- pstate[i, 4] * gamma

}

# Priors for fixed effects

for(k in 1:9) {

theta[k] ~ dnorm(0, .001)

}

gamma <- -2000

}

Page 25: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

Page 26: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

p1 = 1log(p2) = Ipst1 ∗ θ1 + Ipst2 ∗ θ2 + Ipst3 ∗ θ3 + Ipst4 ∗ θ4

log(p3) = Ipst1 ∗ θ5 + Ipst2 ∗ θ6 + Ipst3 ∗ θ7 + Ipst4 ∗ γlog(p4) = Ipst1 ∗ θ8 + Ipst2 ∗ θ9 + Ipste3 ∗ γ + Ipst4 ∗ γ

Page 27: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

Median Ci2.5 Ci97.5

theta[1] -2.04 -2.06 -2.00theta[2] 0.80 0.76 0.83theta[3] -1.27 -1.35 -1.19theta[4] -1.52 -1.68 -1.36theta[5] -2.71 -2.75 -2.67theta[6] -0.79 -0.84 -0.73theta[7] 0.81 0.77 0.86theta[8] -3.95 -4.02 -3.88theta[9] -1.55 -1.63 -1.48

Page 28: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

p1 = 1log(p2) = Ipst1∗−2.04+Ipst2∗0.80+Ipst3∗−1.27+Ipst4∗−1.52log(p3) = Ipst1∗−2.71+Ipst2∗−0.79+Ipst3∗0.81+Ipst4∗−2000log(p4) = Ipst1∗−3.95+ Ipst2∗−1.55+ Ipst3∗γ+ Ipst4∗−2000

p1 = 1log(p2) = −2.04log(p3) = −2.71log(p4) = −3.95

Σp = 1.22

π1 = 0.82 π2 = 0.11 π3 = 0.05 π4 = 0.02

Page 29: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

p1 = 1log(p2) = −2.04log(p3) = −2.71log(p4) = −3.95

Σp = 1.22

π1 = 0.82 π2 = 0.11 π3 = 0.05 π4 = 0.02

Page 30: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

p1 = 1log(p2) = −2.04log(p3) = −2.71log(p4) = −3.95

Σp = p1 + p2 + p3 + p4

Σp = 1.22

π1 = 0.82 π2 = 0.11 π3 = 0.05 π4 = 0.02

Page 31: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

p1 = 1log(p2) = −2.04log(p3) = −2.71log(p4) = −3.95

Σp = 1 + e−2.04 + e−2.71 + e−3.95

Σp = 1.22

π1 = 0.82 π2 = 0.11 π3 = 0.05 π4 = 0.02

Page 32: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

p1 = 1log(p2) = −2.04log(p3) = −2.71log(p4) = −3.95

Σp = 1 + 0.13 + 0.07 + 0.02

Σp = 1.22

π1 = 0.82 π2 = 0.11 π3 = 0.05 π4 = 0.02

Page 33: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

p1 = 1log(p2) = −2.04log(p3) = −2.71log(p4) = −3.95

Σp = 1.22

π1 = 0.82 π2 = 0.11 π3 = 0.05 π4 = 0.02

Page 34: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

p1 = 1log(p2) = −2.04log(p3) = −2.71log(p4) = −3.95

Σp = 1.22

π1 = p1Σp

π2 = p2Σp

π3 = p3Σp

π4 = p4Σp

π1 = 0.82π2 = 0.11 π3 = 0.05 π4 = 0.02

Page 35: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

p1 = 1log(p2) = −2.04log(p3) = −2.71log(p4) = −3.95

Σp = 1.22

π1 = 11.22 π2 = e−2.04

1.22 π3 = e−2.71

1.22 π4 = e−3.95

1.22

π1 = 0.82π2 = 0.11 π3 = 0.05 π4 = 0.02

Page 36: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

p1 = 1log(p2) = −2.04log(p3) = −2.71log(p4) = −3.95

Σp = 1.22

π1 = 0.82 π2 = 0.11 π3 = 0.05 π4 = 0.02

Page 37: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionResults

State Probability of transition

Pre

vio

us

Cu

rren

t CredibilityInterval

n Observed Median 2.5 % 97.5 %Low Low 37,259 0.822 0.822 0.819 0.825Low High 4,870 0.107 0.107 0.105 0.110Low dry 2,487 0.055 0.055 0.053 0.057Low culled 720 0.016 0.016 0.015 0.017High Low 3,770 0.258 0.257 0.251 0.264High High 8,349 0.570 0.570 0.563 0.579High dry 1,718 0.117 0.117 0.113 0.123High culled 798 0.055 0.054 0.051 0.058dry Low 2,647 0.283 0.283 0.274 0.292dry High 745 0.080 0.079 0.075 0.085dry dry 5,967 0.638 0.638 0.627 0.646first Low 863 0.820 0.821 0.797 0.842first High 189 0.180 0.179 0.158 0.203

Page 38: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Outline

1 BackgroundMilk RecordingDataSomatic Cell Count

2 State TransitionState DefinitionState TransitionsData

3 A Simple ModelModelWinBUGS codeResults

4 Adding ComplexitySCC VariationModelWinBUGS codeResults

5 Discussion

Page 39: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Somatic Cell CountFactors of variation

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0 100 200 300 400

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150

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250

300

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atic

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l Cou

nt SCC varies with:

Stage of lactationParity

Parity 1 vs. > 1

Page 40: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Somatic Cell CountFactors of variation

●●●

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0 100 200 300 400

050

100

150

200

250

300

Days in Milk

Som

atic

Cel

l Cou

nt

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0 100 200 300 400

050

100

150

200

250

300

Days in Milk

Som

atic

Cel

l Cou

nt

SCC varies with:

Stage of lactationParity

Parity 1 vs. > 1

Page 41: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionModel

Stateijk ∼ Multinomial(πijk)

ln(πijk

π1jk) =

4∑i ′=1

I [State i ′

i(j−1)k ](αi ′i +

∑Xijkβ

i ′i + ui ′

ik)

ui ′ik ∼ MVN(0,Σu)

State i

Cow-recording j

Herd k

Previous State i ′

Page 42: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionModel

Stateijk ∼ Multinomial(πijk)

ln(πijk

π1jk) =

4∑i ′=1

I [State i ′

i(j−1)k ](αi ′i +

∑Xijkβ

i ′i + ui ′

ik)

ui ′ik ∼ MVN(0,Σu)

State i

Cow-recording j

Herd k

Previous State i ′

Page 43: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionModel

Stateijk ∼ Multinomial(πijk)

ln(πijk

π1jk) =

4∑i ′=1

I [State i ′

i(j−1)k ](αi ′i +

∑Xijkβ

i ′i + ui ′

ik)

ui ′ik ∼ MVN(0,Σu)

State i

Cow-recording j

Herd k

Previous State i ′

Page 44: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionWinBUGS code

model

{

for (i in 1:N) {

State[i, 1:4] ~ dmulti(pi[i, 1:4], 1)

for (j in 1:4) {

pi[i, j] <- p[i, j]/sum(p[i, ])

}

p[i, 1] <- 1

Page 45: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionWinBUGS code

# transition to High

log(p[i, 2]) <- beta[1, i] + beta[2, i] + beta[3, i] + beta[4, i]

## from Low

beta[1, i] <- pstate[i, 1] * (

theta[1] + u1[hd_id[i], 1] + par2[i] * theta[2] +

(1 - par2[i]) * (Dim[i] * theta[3] + pow(Dim[i], 2) * theta[4]) +

par2[i] * (Dim[i] * theta[5] + pow(Dim[i], 2) * theta[6]))

## from High

beta[2, i] <- pstate[i, 2] * (

theta[7] + u1[hd_id[i], 2] + par2[i] * theta[8] +

(1 - par2[i]) * (Dim[i] * theta[9] + pow(Dim[i], 2) * theta[10]) +

par2[i] * (Dim[i] * theta[11] + pow(Dim[i], 2) * theta[12]))

## from dry

beta[3, i] <- pstate[i, 3] * (

par2[i] * (1 - day100[i]) * (theta[13] + u1[hd_id[i], 3]) +

day100[i] * gamma)

## from first

beta[4, i] <- pstate[i, 4] * (

theta[14] + u1[hd_id[i], 4] + par2[i] * gamma)

Page 46: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionWinBUGS code

# transition to High

log(p[i, 2]) <- beta[1, i] + beta[2, i] + beta[3, i] + beta[4, i]

## from Low

beta[1, i] <- pstate[i, 1] * (

theta[1] + u1[hd_id[i], 1] + par2[i] * theta[2] +

(1 - par2[i]) * (Dim[i] * theta[3] + pow(Dim[i], 2) * theta[4]) +

par2[i] * (Dim[i] * theta[5] + pow(Dim[i], 2) * theta[6]))

## from High

beta[2, i] <- pstate[i, 2] * (

theta[7] + u1[hd_id[i], 2] + par2[i] * theta[8] +

(1 - par2[i]) * (Dim[i] * theta[9] + pow(Dim[i], 2) * theta[10]) +

par2[i] * (Dim[i] * theta[11] + pow(Dim[i], 2) * theta[12]))

## from dry

beta[3, i] <- pstate[i, 3] * (

par2[i] * (1 - day100[i]) * (theta[13] + u1[hd_id[i], 3]) +

day100[i] * gamma)

## from first

beta[4, i] <- pstate[i, 4] * (

theta[14] + u1[hd_id[i], 4] + par2[i] * gamma)

Page 47: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionWinBUGS code

# transition to High

log(p[i, 2]) <- beta[1, i] + beta[2, i] + beta[3, i] + beta[4, i]

## from Low

beta[1, i] <- pstate[i, 1] * (

theta[1] + u1[hd_id[i], 1] + par2[i] * theta[2] +

(1 - par2[i]) * (Dim[i] * theta[3] + pow(Dim[i], 2) * theta[4]) +

par2[i] * (Dim[i] * theta[5] + pow(Dim[i], 2) * theta[6]))

## from High

beta[2, i] <- pstate[i, 2] * (

theta[7] + u1[hd_id[i], 2] + par2[i] * theta[8] +

(1 - par2[i]) * (Dim[i] * theta[9] + pow(Dim[i], 2) * theta[10]) +

par2[i] * (Dim[i] * theta[11] + pow(Dim[i], 2) * theta[12]))

## from dry

beta[3, i] <- pstate[i, 3] * (

par2[i] * (1 - day100[i]) * (theta[13] + u1[hd_id[i], 3]) +

day100[i] * gamma)

## from first

beta[4, i] <- pstate[i, 4] * (

theta[14] + u1[hd_id[i], 4] + par2[i] * gamma)

Page 48: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionWinBUGS code

# transition to High

log(p[i, 2]) <- beta[1, i] + beta[2, i] + beta[3, i] + beta[4, i]

## from Low

beta[1, i] <- pstate[i, 1] * (

theta[1] + u1[hd_id[i], 1] + par2[i] * theta[2] +

(1 - par2[i]) * (Dim[i] * theta[3] + pow(Dim[i], 2) * theta[4]) +

par2[i] * (Dim[i] * theta[5] + pow(Dim[i], 2) * theta[6]))

## from High

beta[2, i] <- pstate[i, 2] * (

theta[7] + u1[hd_id[i], 2] + par2[i] * theta[8] +

(1 - par2[i]) * (Dim[i] * theta[9] + pow(Dim[i], 2) * theta[10]) +

par2[i] * (Dim[i] * theta[11] + pow(Dim[i], 2) * theta[12]))

## from dry

beta[3, i] <- pstate[i, 3] * (

par2[i] * (1 - day100[i]) * (theta[13] + u1[hd_id[i], 3]) +

day100[i] * gamma)

## from first

beta[4, i] <- pstate[i, 4] * (

theta[14] + u1[hd_id[i], 4] + par2[i] * gamma)

Page 49: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionWinBUGS code

# transition to High

log(p[i, 2]) <- beta[1, i] + beta[2, i] + beta[3, i] + beta[4, i]

## from Low

beta[1, i] <- pstate[i, 1] * (

theta[1] + u1[hd_id[i], 1] + par2[i] * theta[2] +

(1 - par2[i]) * (Dim[i] * theta[3] + pow(Dim[i], 2) * theta[4]) +

par2[i] * (Dim[i] * theta[5] + pow(Dim[i], 2) * theta[6]))

## from High

beta[2, i] <- pstate[i, 2] * (

theta[7] + u1[hd_id[i], 2] + par2[i] * theta[8] +

(1 - par2[i]) * (Dim[i] * theta[9] + pow(Dim[i], 2) * theta[10]) +

par2[i] * (Dim[i] * theta[11] + pow(Dim[i], 2) * theta[12]))

## from dry

beta[3, i] <- pstate[i, 3] * (

par2[i] * (1 - day100[i]) * (theta[13] + u1[hd_id[i], 3]) +

day100[i] * gamma)

## from first

beta[4, i] <- pstate[i, 4] * (

theta[14] + u1[hd_id[i], 4] + par2[i] * gamma)

Page 50: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionTransition Matrix for Primiparous Cows

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Page 52: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

State transitionTransition Between Low and High SCC

0.0

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Previous State: SCC < 200,000 cells/mL

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lity

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lity

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Previous State: SCC < 200,000 cells/mL

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lity

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lity

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Previous State: SCC < 200,000 cells/mL

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ition

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lity

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ition

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Previous State: SCC < 200,000 cells/mL

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lity

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Previous State: SCC > 200,000 cells/mL

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lity

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lity

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rans

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Previous State: SCC > 200,000 cells/mL

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lity

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babi

lity

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rans

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Previous State: SCC > 200,000 cells/mL

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lity

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ition

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babi

lity

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rans

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Previous State: SCC > 200,000 cells/mL

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Current State − Parity > 1:

< 200,000 > 200,000 dry culled

< 200,000 > 200,000 dry culled

Page 53: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Prediction of BMSCCFrom Individual Cows to Bulk Milk

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Page 54: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Outline

1 BackgroundMilk RecordingDataSomatic Cell Count

2 State TransitionState DefinitionState TransitionsData

3 A Simple ModelModelWinBUGS codeResults

4 Adding ComplexitySCC VariationModelWinBUGS codeResults

5 Discussion

Page 55: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Discussion

The model described the data well

Takes a long time to run in WinBUGS (∼ 30seconds/iteration)

Coefficients can be interpreted as odds-ratios for simplemodels

Model results must be interpreted by generatingpredictions in more complex cases

Page 56: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Discussion

This type of model could be applied to a wide range ofsituations in Veterinary Epidemiology

e.g. locomotion scores, SIR models . . .

MCMC as implemented in WinBUGS converge slowly,even for simple models

Page 57: Multi state

ModellingState

Transitions

AurelienMadouasse

Background

Milk Recording

Data

Somatic CellCount

StateTransition

State Definition

StateTransitions

Data

A SimpleModel

Model

WinBUGS code

Results

AddingComplexity

SCC Variation

Model

WinBUGS code

Results

Discussion

Acknowledgments

Prof. Martin Green

Dr Jon HuxleyDr Andrew Bradley

School of Vetrinary Medicine and Science

University of Nottingham

Prof. William BrowneSchool of Clinical Veterinary Sciences

University of Bristol