Heterogeneity of variance by sire breed, sex, and dam breed in 200- and 365-day weights of beef cattle from a top cross experiment.

Abstract

ABSTRACT:The nature of the heterogeneity of variance for 200-and 365-d weights by sex, sire breed, and dam breed subclasses was studied. Data consisted of records for weaning f n = 7,829) and yearling ( n = 7,367) weights of progeny from 673 and 672 sires, respectively, from 22 breeds that have been evaluated in the Germ Plasm Evaluation Program at the U.S. Meat Animal Research Center, Clay Center, NE. Sires were mated to Hereford and Angus cows. Each trait was analyzed separately. Three studies were undertaken separately to investigate heterogeneity due to the different factors (i.e, sire breed, sex, or dam breed). Only data from seven sire breeds were used to study the factor sire breed, but all data (22 sire breeds) were used to study the factors sex and dam breed. In each study, three sire and dam models with records of animals of the four sex x dam breed combinations considered different traits and with the same model equation, but covariance structures for random effects (sires, dams, and residuals) of increasing generality were fitted. First, (co)variances across subclasses were assumed equal. Second, correlations and fractions of phenotypic variance were assumed equal but phenotypic variance differed by sire breed, sex, or dam breed as appropriate. Third, variances and covariances were different for each subclass of the factor under study. Variance components were estimated by derivative-free REML. Models for each trait and each factor were compared through likelihood ratio tests. For both traits, variances differed ( P < .02) in scale, but not as fractions of phenotypic

Multiple-breed reaction norm animal model accounting for robustness and heteroskedastic in a Nelore–Angus crossed population

“…Finally, the residual variance was greater for bulls (τ S 1 ) than for steers (τ S 2 ) and heifers (τ S 3 ). Similar residual heteroscedasticity associated with the sex effect has been previously observed for growth traits in beef cattle (Garrick et al, 1989;Rodriguez-Almeida et al, 1995).…”

Avaliação de procedimentos na estimação de parâmetros genéticos em bovinos de corte

“…Uma abordagem interessante sobre o assunto pode ser vista em BROWNIE et al (1990). No melhoramento animal, quando a heterogeneidade de variância dos efeitos do modelo não é devidamente estudada, pode ocorrer predição viciada do valor genético e, conseqüentemente, das DEPs dos animais (RODRIGUEZ-ALMEIDA et al, 1995a, 1995b. Segundo MEUWISSEN et al (1996), apenas com a correção da heterogeneidade de variâncias dentro de rebanhos em dados de produção de leite o viés dos valores genéticos reduziu em cerca de 19%.…”

Relações entre as capacidades preditas de transmissão de touros Gir e a produção de leite de suas filhas puras e mestiças

“…O uso do modelo animal na avaliação de animais cruzados tem-se intensificado nos últimos anos (ARNOLD et al, 1992). Em inúmeros trabalhos, utilizaram-se os procedimentos do modelo animal sob a metodologia dos modelos mistos, sendo abundantes na literatura os trabalhos com bovinos de corte (GREGORY et al, 1994(GREGORY et al, , 1995aMEYER et al, 1994;RODRÍGUEZ-ALMEIDA et al, 1995;e VAN VLECK e CUNDIFF, 1994). Os raros trabalhos com gado de leite são de DIM (1974), que reportou ordenação similar de touros, quando as avaliações genéticas dos mesmos basearam-se nos desempenhos produtivos de filhas puras ou mestiças, e de RUVUNA e McDANIEL (1983), que estudaram a relação entre os valores genéticos de, respectivamente, 97 e 95 touros da raça Holandesa e Suíça Parda e o desempenho produtivo de suas 328 filhas mestiças.…”