title: Random regression models using different functions to model milk flow in dairy cows.
abstract: We analyzed 75,555 test-day milk flow records from 2175 primiparous Holstein cows that calved between 1997 and 2005. Milk flow was obtained by dividing the mean milk yield (kg) of the 3 daily milking by the total milking time (min) and was expressed as kg/min. Milk flow was grouped into 43 weekly classes. The analyses were performed using a single-trait Random Regression Models that included direct additive genetic, permanent environmental, and residual random effects. In addition, the contemporary group and linear and quadratic effects of cow age at calving were included as fixed effects. Fourth-order orthogonal Legendre polynomial of days in milk was used to model the mean trend in milk flow. The additive genetic and permanent environmental covariance functions were estimated using random regression Legendre polynomials and B-spline functions of days in milk. The model using a third-order Legendre polynomial for additive genetic effects and a sixth-order polynomial for permanent environmental effects, which contained 7 residual classes, proved to be the most adequate to describe variations in milk flow, and was also the most parsimonious. The heritability in milk flow estimated by the most parsimonious model was of moderate to high magnitude.
authors.affiliation: Departamento de Zootecnia, Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista, Jaboticabal, SP, Brasil monyka.laureano@gmail.com.
authors.forename: M M M
authors.initials: MM
authors.lastname: Laureano
authors.affiliation: Agência Paulista de Tecnologia dos Agronegócios, Pólo Regional Centro Leste, Ribeirão Preto, SP, Brasil.
authors.forename: A B
authors.initials: AB
authors.lastname: Bignardi
authors.affiliation: Agência Paulista de Tecnologia dos Agronegócios, Pólo Regional Centro Leste, Ribeirão Preto, SP, Brasil.
authors.forename: L
authors.initials: L
authors.lastname: El Faro
authors.affiliation: Agência Paulista de Tecnologia dos Agronegócios, Pólo Regional Centro Leste, Ribeirão Preto, SP, Brasil.
authors.forename: V L
authors.initials: VL
authors.lastname: Cardoso
authors.affiliation: Departamento de Zootecnia, Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista, Jaboticabal, SP, Brasil.
authors.forename: H
authors.initials: H
authors.lastname: Tonhati
authors.affiliation: Departamento de Zootecnia, Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista, Jaboticabal, SP, Brasil.
authors.forename: L G
authors.initials: LG
authors.lastname: Albuquerque
mesh_terms: D000818:Animals; D002417:Cattle; D003611:Dairy Products; D056726:Genetic Association Studies; D008892:Milk; D010641:Phenotype; D019655:Quantitative Trait, Heritable; D012044:Regression Analysis