title: Random Regression Models Using Legendre Polynomials to Estimate Genetic Parameters for Test-day Milk Protein Yields in Iranian Holstein Dairy Cattle.
abstract: The objective of this study was to estimate the genetic parameters of milk protein yields in Iranian Holstein dairy cattle. A total of 1,112,082 test-day milk protein yield records of 167,269 first lactation Holstein cows, calved from 1990 to 2010, were analyzed. Estimates of the variance components, heritability, and genetic correlations for milk protein yields were obtained using a random regression test-day model. Milking times, herd, age of recording, year, and month of recording were included as fixed effects in the model. Additive genetic and permanent environmental random effects for the lactation curve were taken into account by applying orthogonal Legendre polynomials of the fourth order in the model. The lowest and highest additive genetic variances were estimated at the beginning and end of lactation, respectively. Permanent environmental variance was higher at both extremes. Residual variance was lowest at the middle of the lactation and contrarily, heritability increased during this period. Maximum heritability was found during the 12th lactation stage (0.213±0.007). Genetic, permanent, and phenotypic correlations among test-days decreased as the interval between consecutive test-days increased. A relatively large data set was used in this study; therefore, the estimated (co)variance components for random regression coefficients could be used for national genetic evaluation of dairy cattle in Iran.
authors.affiliation: Department of Animal Science, University College of Agriculture and Natural Resources, University of Tehran, Karaj 31587-11167, Iran
authors.forename: Masoumeh
authors.initials: M
authors.lastname: Naserkheil
authors.affiliation: Department of Animal Science, University College of Agriculture and Natural Resources, University of Tehran, Karaj 31587-11167, Iran
authors.forename: Seyed Reza
authors.initials: SR
authors.lastname: Miraie-Ashtiani
authors.affiliation: Department of Animal Science, University College of Agriculture and Natural Resources, University of Tehran, Karaj 31587-11167, Iran
authors.forename: Ardeshir
authors.initials: A
authors.lastname: Nejati-Javaremi
authors.affiliation: Department of Animal Life and Resources, Hankyong National University, Ansung 456-749, Korea
authors.forename: Jihyun
authors.initials: J
authors.lastname: Son
authors.affiliation: Department of Animal Life and Resources, Hankyong National University, Ansung 456-749, Korea
authors.forename: Deukhwan
authors.initials: D
authors.lastname: Lee
keywords: Holstein Dairy Cattle; Milk Protein Yields; Random Regression Model; Test-day Records