ASAS/ADSA 2001 Conference (1) 2001 Variance of effects of lactation stage within herd by herd yield N. Gengler 1,2, B. Auvray *,1, and G.R. Wiggans 3 1 Gembloux Agricultural University, Belgium 2 National Fund for Scientific Research, Brussels, Belgium 3 Agricultural Research Service, USDA, Beltsville, MD

2001 ASAS/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

2001 ASAS/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

2001 ASAS/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

2001 ASAS/ADSA 2001 Conference (5) Mean yields in data sets

2001 ASAS/ADSA 2001 Conference (6) Phenotypic variances for milk (x100 kg 2 ) days in milk

2001 ASAS/ADSA 2001 Conference (7) days in milk Heritabilities for milk yield  Incomplete model:  Complete model: days in milk

2001 ASAS/ADSA 2001 Conference (8) Herd stage effect for milk yield days in milk

2001 ASAS/ADSA 2001 Conference (9) Herd stage effect for fat yield days in milk

2001 ASAS/ADSA 2001 Conference (10) Herd stage effect for protein yield days in milk

2001 ASAS/ADSA 2001 Conference (11) Herd stage effect for SCS days in milk

2001 ASAS/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

2001 ASAS/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