title: Comparison of random  regression models to estimate genetic parameters for milk production in Guzerat  (Bos indicus) cows.
abstract: Random  regression models have been widely used to estimate genetic parameters that influence  milk production in Bos taurus breeds, and more recently in B. indicus breeds. With the aim of finding appropriate random regression model to  analyze milk yield, different parametric functions were compared, applied to  20,524 test-day milk yield records of 2816 first-lactation Guzerat (B.  indicus) cows in Brazilian herds. The records were analyzed by random  regression models whose random effects were additive genetic, permanent environmental  and residual, and whose fixed effects were contemporary group, the covariable  cow age at calving (linear and quadratic effects), and the herd lactation  curve. The additive genetic and permanent environmental effects were modeled by  the Wilmink function, a modified Wilmink function (with the second term divided  by 100), a function that combined third-order Legendre polynomials with the  last term of the Wilmink function, and the Ali and Schaeffer function. The  residual variances were modeled by means of 1, 4, 6, or 10 heterogeneous  classes, with the exception of the last term of the Wilmink function, for which  there were 1, 3, 6, or 10 classes. The models gave similar hereditability  estimates, ranging from 0.20 to 0.33. Genetic correlations between adjacent  records were high values (0.83-0.99), but they declined when the interval  between the test-day records increased, and were negative between the first and  last records. The model employing the Ali and Schaeffer function with six  residual variance classes was the most suitable for fitting the data.
authors: Departamento de Zootecnia, Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista Júlio de Mesquita Filho, Jaboticabal, SP, Brasil. daniel_jordan2008@hotmail.com
authors: D J A
authors: DJ
authors: Santos
authors: M G C D
authors: MG
authors: Peixoto
authors: R R Aspilcueta
authors: RR
authors: Borquis
authors: R S
authors: RS
authors: Verneque
authors: J C C
authors: JC
authors: Panetto
authors: H
authors: H
authors: Tonhati
mesh_terms: D000818:Animals; D002417:Cattle; D005260:Female; D007774:Lactation / Q000235:genetics*; D008892:Milk / Q000378:metabolism*; D008957:Models, Genetic; D010641:Phenotype; D012044:Regression Analysis