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1 Dept. of Animal Science, University of Tennessee, Knoxville 37996
2 Holstein Association USA Inc., Brattleboro, VT 05302
Corresponding author: C. Dehow; e-mail: cdechow{at}tennessee.edu.
The objectives of the current study were to investigate the relationship between body condition score (BCS) and dairy form and changes in genetic parameters for BCS and dairy form within and across lactations and age. Body condition score and dairy form were obtained from the Holstein Association USA, Inc. Records were edited to include those cows classified between 24 and 60 mo of age and between 0 and 335 d in milk (DIM). A minimum of 20 daughters per sire and 15 cows per herd-classification visit were required. The dataset consisted of 135,178 records from 119,215 cows. Repeatability, multiple trait, and random regression models were used to analyze the data. All models included fixed effects for herd-classification visit, age within lactations 1, 2, and 3 or higher, and 5th-order polynomials for DIM. Random effects included sire and permanent environment for all models. Random regression models included age at classification nested within sire or DIM and lactation number nested within sire. Genetic variance for both BCS and dairy form was lowest in early lactation and highest in midlactation. Genetic correlations within and across lactations were high. The genetic correlation between DIM 0 in lactation 1 and DIM 305 in lactation 3 was estimated to be 0.77 for BCS and 0.60 for dairy form. The genetic correlation estimate between 30 mo of age at classification and 50 mo of age at classification was 0.94 for both dairy form and BCS. The repeatability models appeared to generate accurate evaluations for BCS or dairy form at all ages and stages of lactation.
Key Words: body condition score • dairy form • random regression
Abbreviation key: BCS = body condition score, BCSx = BCS on DIM X, BCHX-Y = BCS on DIM X minus BCS on DIM Y, BCHDP = BCS on DIM 0 in lactation 2 - DIM 305 in lactation 1, DFX = dairy form on DIM X, DCHX-Y = dairy form on DIM X minus dairy form on DIM Y, HEV = heterogeneous residual variance, HOV = homogeneous residual variance, L = lactation number, LG = lactation group, LG1 = lactation group 1, LG2 = lactation group 2, LG3 = lactation group 3, LP = Legendre polynomial, LP0 = intercept, LP1 = linear Legendre polynomial, LP2 = quadratic Legendre polynomial, MDRR = multidimensional random regression, MT = multiple trait, PE = permanent environment, RPT = repeatability, RRA = random regression on age
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