asas/adsa 2001 conference (1) 2001 variance of effects of lactation stage within herd by herd yield...
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ASAS/ADSA 2001 Conference (1) 2001
Variance of effects of lactation stage within herd by herd yield
N. Gengler1,2, B. Auvray*,1, and G.R. Wiggans3 1 Gembloux Agricultural University, Belgium2 National Fund for Scientific Research, Brussels, Belgium3 Agricultural Research Service, USDA, Beltsville, MD
2001ASAS/ADSA 2001 Conference (2)
Heterogeneity of (co)variances
Important issue in test-day models More important than in 305 d models:
– not only overall variance– also (co)variances– among all days in milk
Important factor: stage x herd yield Equivalent to
– herd specific lactation curves
2001ASAS/ADSA 2001 Conference (3)
Data
Test-day yields from first-lactation Holsteins Milk, fat, protein and SCS From New York, Wisconsin, and California Herds with different annual milk yields:
– low (< 7257 kg)– medium (9072 to 9525 kg)– high (> 11,340 kg)
Adjusted additively for age and lactation stage
2001ASAS/ADSA 2001 Conference (4)
Test-day models
EM-REML (co)variance component estimation Two random regression models Constant, linear and quadratic Legendre’s
polynomials First model (“incomplete model”):
– animal genetic regressions– animal permanent environment regressions
Second model (“complete model”):– herd x 2 years of calving random regressions
added
2001ASAS/ADSA 2001 Conference (5)
Mean yields in data setsMean yields in data sets
High Medium Low
Records 75838 74845 71996
Milk 35.4 kg 28.8 kg 25.6 kg
Fat 1282.2 g 1055.2 g 922.6 g
Protein 1034.0 g 861.2 g 762.9 g
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Phenotypic variances for milkPhenotypic variances for milk(x100 kg(x100 kg22))
01000
20003000
40005000
60007000
8000
5 35 65 95 125 155 185 215 245 275 305 335 365
High complete Medium complete Low complete
High Medium Low
days in milkdays in milk
2001ASAS/ADSA 2001 Conference (7)
days in milkdays in milk
0.000.100.200.300.40
5 65 125 185 245 305 365
High Medium Low
Heritabilities for milk yieldHeritabilities for milk yield
Incompletemodel:
Completemodel:
0.000.100.200.300.40
5 65 125 185 245 305 365
days in milkdays in milk
2001ASAS/ADSA 2001 Conference (8)
Herd stage effect for milk yieldHerd stage effect for milk yield
0.00
0.10
0.20
5 65 125 185 245 305 365
High Medium Low
days in milkdays in milk
2001ASAS/ADSA 2001 Conference (9)
Herd stage effect for fat yield Herd stage effect for fat yield
0.00
0.10
0.20
5 65 125 185 245 305 365
High Medium Low
days in milkdays in milk
2001ASAS/ADSA 2001 Conference (10)
Herd stage effect for protein yield Herd stage effect for protein yield
0.00
0.10
0.20
5 65 125 185 245 305 365
High Medium Low
days in milkdays in milk
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Herd stage effect for SCS Herd stage effect for SCS
0.00
0.10
0.20
5 65 125 185 245 305 365
High Medium Low
days in milkdays in milk
2001ASAS/ADSA 2001 Conference (12)
Conclusions
Herd yield level influences (co)variances Not only variance level, also effect of days in
milk on variances Environmental lactation stage within herd not
negligible for milk, fat and protein especially:– at the beginning of the lactation– to a smaller extend at the end
Cleans heritabilities, no longer unlikely values of h2 in early days in milk
2001ASAS/ADSA 2001 Conference (13)
Implications for test-day models
Heterogeneity of (co)variances an issue needs to be considered
Herd yield and herd lactation stage effects need to be considered
If unlikely heritability shapes herd lactation stage effects to be included