title: Quantitative genetic study of age at subsequent rebreeding in Nellore cattle by using survival analysis.
abstract: The continuous trait age at subsequent rebreeding (ASR) was evaluated using survival analysis in Nellore breed cows that conceived for the first time at approximately 14 months of age. This methodology was chosen because the restricted breeding season produces censored data. The dataset contained 2885 records of ASR (in days). Records of females that did not produce calves in the following year after being exposed to a sire were considered censored (48.3% of the total). The statistical model used was a Weibull mixed survival model, which included fixed effects of contemporary groups (CG) and period and a random effect of individual animal. The effect of contemporary groups on ASR was significant (P < 0.01). Heritabilities obtained for ASR were 0.03 and 0.04 in logarithmic and original scales, respectively. These results indicate that the genetic selection response for subsequent reproduction of 2-year-old Nellore breed females is not expected to be effective based on survival analysis. Furthermore, these results suggest that environmental improvement is fundamental to this important trait. It should be highlighted that an increase in the average date of birth can produce an adverse effect in the future, since this cannot be compensated by genetic improvement.
authors.affiliation: Universidade Estadual Paulista, Botucatu, SP, Brasil.
authors.forename: M H
authors.initials: MH
authors.lastname: Van Melis
authors.affiliation: Universidade Estadual Paulista, Botucatu, SP, Brasil.
authors.forename: L G G
authors.initials: LG
authors.lastname: Figueiredo
authors.affiliation: Universidade Estadual Paulista, Jaboticabal, Brasil.
authors.forename: H N
authors.initials: HN
authors.lastname: Oliveira
authors.affiliation: Universidade de São Paulo, Pirassununga, SP, Brasil.
authors.forename: J P
authors.initials: JP
authors.lastname: Eler
authors.affiliation: University of Wisconsin, Madison, USA.
authors.forename: G J M
authors.initials: GJ
authors.lastname: Rosa
authors.affiliation: Universidade Federal de Mato Grosso, Campus de Rondonópolis, Rondonópolis, MT, Brasil.
authors.forename: M L
authors.initials: ML
authors.lastname: Santana
authors.affiliation: Instituto de Genética e Bioquimíca, Universidade Federal de Uberlândia, Campus de Patos de Minas, Patos de Minas, MG, Brasil.
authors.forename: F M
authors.initials: FM
authors.lastname: Rezende
authors.affiliation: Universidade de São Paulo, Pirassununga, SP, Brasil jbferraz@usp.br.
authors.forename: J B S
authors.initials: JB
authors.lastname: Ferraz
mesh_terms: D000367:Age Factors; D000818:Animals; D001947:Breeding; D002417:Cattle; D004777:Environment; D005260:Female; D010641:Phenotype; D012098:Reproduction / Q000235:genetics*; D012641:Selection, Genetic; D016019:Survival Analysis