title: Reaction norm model to describe environmental sensitivity across first lactation in dairy cattle under tropical conditions.
abstract: Reaction norm models have been widely used to study genotype by environment interaction (G × E) in animal breeding. The objective of this study was to describe environmental sensitivity across first lactation in Brazilian Holstein cows using a reaction norm approach. A total of 50,168 individual monthly test day (TD) milk yields (10 test days) from 7476 complete first lactations of Holstein cattle were analyzed. The statistical models for all traits (10 TDs and for 305-day milk yield) included the fixed effects of contemporary group, age of cow (linear and quadratic effects), and days in milk (linear effect), except for 305-day milk yield. A hierarchical reaction norm model (HRNM) based on the unknown covariate was used. The present study showed the presence of G × E in milk yield across first lactation of Holstein cows. The variation in the heritability estimates implies differences in the response to selection depending on the environment where the animals of this population are evaluated. In the average environment, the heritabilities for all traits were rather similar, in range from 0.02 to 0.63. The scaling effect of G × E predominated throughout most of lactation. Particularly during the first 2 months of lactation, G × E caused reranking of breeding values. It is therefore important to include the environmental sensitivity of animals according to the phase of lactation in the genetic evaluations of Holstein cattle in tropical environments.
authors.affiliation: Grupo de Melhoramento Animal de Mato Grosso (GMAT), Instituto de Ciências Agrárias e Tecnológicas, Universidade Federal de Mato Grosso, Campus Universitário de Rondonópolis, 78735-901, Rondonópolis, MT, Brazil. annaizabb@hotmail.com.
authors.forename: Annaiza Braga
authors.initials: AB
authors.lastname: Bignardi
authors.affiliation: Centro de Pesquisas de Bovinos de Corte, Instituto de Zootecnia, Caixa Postal 63, Rodovia Carlos Tonanni, km 94, 14160-900, Sertãozinho, SP, Brazil.
authors.forename: Lenira
authors.initials: L
authors.lastname: El Faro
authors.affiliation: Grupo de Melhoramento Animal de Mato Grosso (GMAT), Instituto de Ciências Agrárias e Tecnológicas, Universidade Federal de Mato Grosso, Campus Universitário de Rondonópolis, 78735-901, Rondonópolis, MT, Brazil.
authors.forename: Rodrigo Junqueira
authors.initials: RJ
authors.lastname: Pereira
authors.affiliation: Grupo de Melhoramento Animal de Mato Grosso (GMAT), Instituto de Ciências Agrárias e Tecnológicas, Universidade Federal de Mato Grosso, Campus Universitário de Rondonópolis, 78735-901, Rondonópolis, MT, Brazil.
authors.forename: Denise Rocha
authors.initials: DR
authors.lastname: Ayres
authors.affiliation: Departmento de Zootecnia, Universidade de São Paulo, 13418-900, Piracicaba, SP, Brazil.
authors.forename: Paulo Fernando
authors.initials: PF
authors.lastname: Machado
authors.affiliation: Departamento de Zootecnia, Universidade Estadual Paulista (FCAV/UNESP), 14884-900, Jaboticabal, SP, Brazil.|Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), 71605-001, Brasília, DF, Brazil.
authors.forename: Lucia Galvão
authors.initials: LG
authors.lastname: de Albuquerque
authors.affiliation: Grupo de Melhoramento Animal de Mato Grosso (GMAT), Instituto de Ciências Agrárias e Tecnológicas, Universidade Federal de Mato Grosso, Campus Universitário de Rondonópolis, 78735-901, Rondonópolis, MT, Brazil.
authors.forename: Mário Luiz
authors.initials: ML
authors.lastname: Santana
mesh_terms: D000818:Animals; D001938:Brazil; D002417:Cattle / Q000235:genetics / Q000502:physiology*; D003612:Dairying; D004777:Environment; D005260:Female; D014644:Genetic Variation; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000737:chemistry*; D015233:Models, Statistical; D014329:Tropical Climate
keywords: Breeding; Environment interaction; Holstein; Milk; Selection; Test day