At the same level of production cows with high persistency milk more at the end than the beginning of lactation. Best prediction of persistency is calculated as a function of trait-specific standard lactation curves and the linear regression of a cow’s test day deviations on days in milk.

1. 200420042005
J. B. Cole * and P. M. VanRaden
Animal Improvement Programs Laboratory
Agricutural Research Service, USDA, Beltsville, MD
jcole@aipl.arsusda.gov
Genetic evaluation and best
prediction of lactation
persistency

2. ADSA 2005: Persistency of lactation (2) Cole and VanRaden 20042005
Introduction
 At the same level of production cows
with high persistency milk more at the
end than the beginning of lactation.
 Best prediction of persistency is
calculated as a function of trait-
specific standard lactation curves and
the linear regression of a cow’s test
day deviations on days in milk.

3. ADSA 2005: Persistency of lactation (3) Cole and VanRaden 20042005
Best Prediction
 Selection IndexSelection Index
 Predict missing yields from measured yieldsPredict missing yields from measured yields
 Condense daily into lactation yield andCondense daily into lactation yield and
persistencypersistency
 Only phenotypic covariances are neededOnly phenotypic covariances are needed
 Mean and variance of herd assumed knownMean and variance of herd assumed known
 Reverse predictionReverse prediction
 Daily yield predicted from lactation yieldDaily yield predicted from lactation yield
and persistencyand persistency

4. ADSA 2005: Persistency of lactation (4) Cole and VanRaden 20042005
Reliabilities
 Definition
Squared correlation of estimated
with true persistency
Same as Rel (breeding value)
Single-trait or multi-trait (M, F, P,
SCS)

5. ADSA 2005: Persistency of lactation (5) Cole and VanRaden 20042005
Persistency
VanRaden 1998 6th
WCGALP XXIII:347-350
 DefinitionDefinition
305 daily yield deviations (DIM - DIM305 daily yield deviations (DIM - DIMoo))
Uncorrelated with yield by choosingUncorrelated with yield by choosing
DIMDIMoo
DIMDIMoo werewere 161161,, 159159,, 166166, and, and 155155 forfor
M, F, P, and SCSM, F, P, and SCS
• DIMDIM00 have increased over timehave increased over time
Standardized estimateStandardized estimate

6. ADSA 2005: Persistency of lactation (6) Cole and VanRaden 20042005
Statistical Properties
Available data Rel (Y) Rel (P) Corr (Y,P)
305-d Daily 100% 100% .00
305-d Monthly 97 91 .00
305-d Bimonthly 94 82 .00
100-d RIP 76 33 -.78
15-d test 40 27 -1.00

7. ADSA 2005: Persistency of lactation (7) Cole and VanRaden 20042005
Objective
 Calculate (co)variance components
and breeding values for persistency
of milk (PM), fat (PF), protein (PP),
and SCS (PSCS) in Holsteins
 Estimate genetic correlations among
persistency and yield traits

8. ADSA 2005: Persistency of lactation (8) Cole and VanRaden 20042005
Data
 8,682,138 lactation records from
4,375,938 Holstein cows calving
since January 1, 1997
 Best prediction of persistency
Milk (M), fat (F), protein (P), SCS
Floor and ceiling of ± 4.0
Phenotypic reliability ≥ 50%
 1st
- 5th
lactations (1st
required)

9. ADSA 2005: Persistency of lactation (9) Cole and VanRaden 20042005
Cow with Average Persistency
0
5
10
15
20
25
0 30 60 90 120 150 180 210 240 270 300
Days in Milk
Kilograms
Best Prediction
Standard Curve
Test Days

10. ADSA 2005: Persistency of lactation (10) Cole and VanRaden 20042005
Highest Cow Persistency
0
10
20
30
40
50
60
70
80
90
100
0 30 60 90 120 150 180 210 240 270 300
Days in Milk
Kilograms
Best Prediction
Standard Curve
Test Days

11. ADSA 2005: Persistency of lactation (11) Cole and VanRaden 20042005
Lowest Cow Persistency
0
10
20
30
40
50
60
70
80
90
100
0 30 60 90 120 150 180 210 240 270 300
Days in Milk
Kilograms
Best Prediction
Standard Curve
Test Days

12. ADSA 2005: Persistency of lactation (12) Cole and VanRaden 20042005
Model
Repeatability animal model:
yijkl = hysi + lacj + ak + pek + β(dojk) + eijkl
yijkl = persistency of milk,fat, protein, or SCS
hysi = fixed effect of herd-year-season of calving I
lacj = fixed effect of lactation j
ak = random additive genetic effect of animal k
pek = random permanent environmental effect of animal k
dojk = days open for lactation j of animal k
eijkl = random residual error
ijkljkkkjiijkl e)β(dopealachysy +++++= ijkljkkkjiijkl e)β(dopealachysy +++++=

13. ADSA 2005: Persistency of lactation (13) Cole and VanRaden 20042005
(Co)variance Components
σa
2
σpe
2
σe
2
h2
rept
PM 0.10 0.09 0.85 0.10 0.18
PF 0.07 0.08 0.79 0.07 0.15
PP 0.08 0.07 0.70 0.09 0.17
PSCS 0.02 0.03 0.64 0.03 0.07

14. ADSA 2005: Persistency of lactation (14) Cole and VanRaden 20042005
Correlations Among Persistency Traits
PM PF PP PSCS
PM 0.83 0.87 -0.48
PF 0.72 0.82 -0.41
PP 0.91 0.72 -0.58
PSCS -0.19 -0.11 -0.14
1
Genetic correlations above diagonal, residual correlations below diagonal.

15. ADSA 2005: Persistency of lactation (15) Cole and VanRaden 20042005
Phenotypic Correlations Among
Persistency and Yield
M F P SCS
PM 0.03 0.07 0.07 -0.03
PF 0.05 -0.02 0.08 -0.03
PP 0.04 0.08 0.05 -0.03
PSCS 0.05 0.02 0.04 -0.03

16. ADSA 2005: Persistency of lactation (16) Cole and VanRaden 20042005
Genetic Correlations Among
Persistency and Yield
M F P SCS
PM 0.05 0.10 0.03 -0.04
PF 0.12 0.12 0.00 0.00
PP -0.02 0.08 -0.09 -0.11
PSCS -0.23 -0.28 -0.20 0.41

17. ADSA 2005: Persistency of lactation (17) Cole and VanRaden 20042005
Distribution of Sire PTA
0
10
20
30
40
50
60
70
-0.93 -0.80 -0.66 -0.53 -0.39 -0.26 -0.12 0.01 0.15 0.29 0.42 0.56
PTA PM
Frequency
0
10
20
30
40
50
60
70
-0.73 -0.61 -0.50 -0.39 -0.28 -0.17 -0.06 0.05 0.16 0.28 0.39 0.50
PTA PF
Frequency
0
10
20
30
40
50
60
70
-0.70 -0.59 -0.48 -0.37 -0.27 -0.16 -0.05 0.05 0.16 0.27 0.38 0.48
PTA PP
Frequency
0
10
20
30
40
50
60
70
80
-0.35 -0.29 -0.24 -0.18 -0.13 -0.07 -0.01 0.04 0.10 0.16 0.21 0.27
PTA PSCS
Frequency

18. ADSA 2005: Persistency of lactation (18) Cole and VanRaden 20042005
Conclusions
 Heritabilities and repeatabilities are
low to moderate
 Routine genetic evaluations for
persistency are feasible
 The shape of the lactation curve
may be altered without affecting
production