title: Genetic parameters for growth characteristics of free-range chickens under univariate random regression models.
abstract: Repeated measures from the same individual have been analyzed by using repeatability and finite dimension models under univariate or multivariate analyses. However, in the last decade, the use of random regression models for genetic studies with longitudinal data have become more common. Thus, the aim of this research was to estimate genetic parameters for body weight of four experimental chicken lines by using univariate random regression models. Body weight data from hatching to 84 days of age (n = 34,730) from four experimental free-range chicken lines (7P, Caipirão da ESALQ, Caipirinha da ESALQ and Carijó Barbado) were used. The analysis model included the fixed effects of contemporary group (gender and rearing system), fixed regression coefficients for age at measurement, and random regression coefficients for permanent environmental effects and additive genetic effects. Heterogeneous variances for residual effects were considered, and one residual variance was assigned for each of six subclasses of age at measurement. Random regression curves were modeled by using Legendre polynomials of the second and third orders, with the best model chosen based on the Akaike Information Criterion, Bayesian Information Criterion, and restricted maximum likelihood. Multivariate analyses under the same animal mixed model were also performed for the validation of the random regression models. The Legendre polynomials of second order were better for describing the growth curves of the lines studied. Moderate to high heritabilities (h(2) = 0.15 to 0.98) were estimated for body weight between one and 84 days of age, suggesting that selection for body weight at all ages can be used as a selection criteria. Genetic correlations among body weight records obtained through multivariate analyses ranged from 0.18 to 0.96, 0.12 to 0.89, 0.06 to 0.96, and 0.28 to 0.96 in 7P, Caipirão da ESALQ, Caipirinha da ESALQ, and Carijó Barbado chicken lines, respectively. Results indicate that genetic gain for body weight can be achieved by selection. Also, selection for body weight at 42 days of age can be maintained as a selection criterion.
authors.affiliation: Department of Animal Science, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil.
authors.forename: Gregori A
authors.initials: GA
authors.lastname: Rovadoscki
authors.affiliation: Department of Animal Science, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil.
authors.forename: Juliana
authors.initials: J
authors.lastname: Petrini
authors.affiliation: Department of Animal Science, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil.
authors.forename: Johanna
authors.initials: J
authors.lastname: Ramirez-Diaz
authors.affiliation: Department of Animal Science, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil.
authors.forename: Simone F N
authors.initials: SF
authors.lastname: Pertile
authors.affiliation: Department of Animal Science, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil.
authors.forename: Fábio
authors.initials: F
authors.lastname: Pertille
authors.affiliation: Department of Animal Science, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil.
authors.forename: Mayara
authors.initials: M
authors.lastname: Salvian
authors.affiliation: Department of Animal Science, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil.
authors.forename: Laiza H S
authors.initials: LH
authors.lastname: Iung
authors.affiliation: Department of Animal Science, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil.
authors.forename: Mary Ana P
authors.initials: MA
authors.lastname: Rodriguez
authors.affiliation: Department of Animal Science, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil.
authors.forename: Aline
authors.initials: A
authors.lastname: Zampar
authors.affiliation: Department of Basic Sciences, University of São Paulo, Pirassununga, SP, 13.635-900, Brazil.
authors.forename: Leila G
authors.initials: LG
authors.lastname: Gaya
authors.affiliation: Department of Basic Sciences, University of São Paulo, Pirassununga, SP, 13.635-900, Brazil.
authors.forename: Rachel S B
authors.initials: RS
authors.lastname: Carvalho
authors.affiliation: Department of Genetics, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil.
authors.forename: Antonio A D
authors.initials: AA
authors.lastname: Coelho
authors.affiliation: Department of Genetics, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil.
authors.forename: Vicente J M
authors.initials: VJ
authors.lastname: Savino
authors.affiliation: Department of Animal Science, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil.
authors.forename: Luiz L
authors.initials: LL
authors.lastname: Coutinho
authors.affiliation: Department of Animal Science, University of São Paulo, Piracicaba, SP, 13.418-900, Brazil gbmourao@usp.br.
authors.forename: Gerson B
authors.initials: GB
authors.lastname: Mourão
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D001835:Body Weight / Q000235:genetics*; D002645:Chickens / Q000235:genetics / Q000502:physiology*; D005260:Female; D008297:Male; D008957:Models, Genetic; D058871:Organic Agriculture; D012044:Regression Analysis
keywords: Legendre polynomials; broiler; growth; heterogenous variance; variance components