title: Estimation of  genetic parameters for partial egg production periods by means of random  regression models.
abstract: We  estimated genetic parameters for egg production in different periods by means  of random regression models, aiming at selection based on partial egg  production from a generation of layers. The production was evaluated for each  individual by recording the number of eggs produced from 20 to 70 weeks of age,  with partial records taken every three weeks for a total of 17 periods. The  covariance functions were estimated with a random regression model by the  restricted maximum likelihood method. A model composed of third-order  polynomials for the additive effect, ninth-order polynomials for the permanent  environment, and a residual variance structure with five distinct classes, was  found to be most suitable for adjusting the egg production data for laying  hens. The heritability estimates varied from 0.04 to 0.14. The genetic  correlations were all positive, varying from 0.10 to 0.99. Selection applied in  partial egg production periods will result in greater genetic profit for the  adjacent periods. However, as the distance in time between periods increases,  selection becomes less efficient. Selection based on the second period (23 to  25 weeks of age), where greater heritability was estimated, would note benefit  the final egg-laying cycle periods.
authors.affiliation: Departamento de Ciências Exatas, Universidade Estadual Paulista Júlio de Mesquita Filho, Jaboticabal, SP, Brazil.
authors.forename: G C
authors.initials: GC
authors.lastname: Venturini
authors.forename: D A
authors.initials: DA
authors.lastname: Grossi
authors.forename: S B
authors.initials: SB
authors.lastname: Ramos
authors.forename: V A R
authors.initials: VA
authors.lastname: Cruz
authors.forename: C G
authors.initials: CG
authors.lastname: Souza
authors.forename: M C
authors.initials: MC
authors.lastname: Ledur
authors.forename: L
authors.initials: L
authors.lastname: El Faro
authors.forename: G S
authors.initials: GS
authors.lastname: Schmidt
authors.forename: D P
authors.initials: DP
authors.lastname: Munari
mesh_terms: D000375:Aging / Q000235:genetics; D000818:Animals; D002645:Chickens / Q000235:genetics*; D040582:Inheritance Patterns / Q000235:genetics; D016013:Likelihood Functions; D008957:Models, Genetic; D010058:Oviposition / Q000235:genetics*; D010641:Phenotype; D012044:Regression Analysis