11 research outputs found
Genetic control of residual variance of yearling weight in nellore beef cattle
There is evidence for genetic variability in residual variance of livestock traits, which offers the potential for selection for increased uniformity of production. Different statistical approaches have been employed to study this topic; however, little is known about the concordance between them. The aim of our study was to investigate the genetic heterogeneity of residual variance on yearling weight (YW; 291.15 ± 46.67) in a Nellore beef cattle population; to compare the results of the statistical approaches, the two-step approach and the double hierarchical generalized linear model (DHGLM); and to evaluate the effectiveness of power transformation to accommodate scale differences. The comparison was based on genetic parameters, accuracy of EBV for residual variance, and cross-validation to assess predictive performance of both approaches. A total of 194,628 yearling weight records from 625 sires were used in the analysis. The results supported the hypothesis of genetic heterogeneity of residual variance on YW in Nellore beef cattle and the opportunity of selection, measured through the genetic coefficient of variation of residual variance (0.10 to 0.12 for the two-step approach and 0.17 for DHGLM, using an untransformed data set). However, low estimates of genetic variance associated with positive genetic correlations between mean and residual variance (about 0.20 for two-step and 0.76 for DHGLM for an untransformed data set) limit the genetic response to selection for uniformity of production while simultaneously increasing YW itself. Moreover, large sire families are needed to obtain accurate estimates of genetic merit for residual variance, as indicated by the low heritability estimates (<0.007). Box-Cox transformation was able to decrease the dependence of the variance on the mean and decreased the estimates of genetic parameters for residual variance. The transformation reduced but did not eliminate all the genetic heterogeneity of residual variance, highlighting its presence beyond the scale effect. The DHGLM showed higher predictive ability of EBV for residual variance and therefore should be preferred over the two-step approach
Índice de seleção bioeconômico para fêmeas de corte da raça nelore
The reproductive efficiency of Nellore females
was described on the basis of sexual precocity,
staying productive in the herd (NP), maternal
productivity (PM) and estimated cost for
maintenance (CM). The combination of these traits
resulted in the bioeconomic maternal revenue
index (RMat) ensures reproductive efficiency.
The index estimates the return in kilograms of live
weight produced per cow per year. In addition, the
composition of calf weight produced was
considered, adding to the PM the information on the
scores of conformation, muscling and early
finishing at weaning, in order to input the calf
biotype. The females considered precocious had
their age at first calving before 30 months. The NP
was expressed by the number of calving till 53
months of age. The CM was calculated according
to the estimated feed intake of dry matter. The
estimated average RMat was 62.02±24.12 kg/
cow/year. Estimates of additive genetic and resi-
dual variances for RMat, using restricted maximum
likelihood under a single trait animal model was
equal to 195.35 and 242.96, respectively. The
heritability estimated was 0.45±0.02, indicating
that RMat is inheritable and can be applied in the
breeding program to improve reproductive
efficiency. The NP was the main component of
variation for RMat. Sires selected based on RMat
tended to have more efficient daughters.A eficiência reprodutiva da fêmea Nelore foi
descrita com base na precocidade sexual,
permanência produtiva no rebanho (NP),
produtividade materna (PM) e custo de mantença
estimado (CM). A combinação dessas caracterís-
ticas deu origem ao índice bioeconômico retorno
maternal (RMat), que estima o retorno em quilos de
peso vivo produzidos por uma vaca em um ano. Em
adição, incluiu-se a composição do peso produzido,
adicionando à PM os escores de conformação,
precocidade e musculatura a desmama, compondo
o biótipo do bezerro. Foram consideradas preco-
ces as fêmeas cuja idade ao primeiro parto foi
inferior a 30 meses. A NP foi expressa pelo número
de partos até 53 meses de idade. O CM foi calcu-
lado em função do consumo estimado de matéria
seca da vaca. O RMat médio estimado foi
62,02±24,12 kg/vaca/ano. As estimativas da
variância genética aditiva e residual do RMat,
usando a metodologia da máxima verossimilhança
restrita, sob um modelo animal unicaracterística,
foram 195,35 e 242,96, respectivamente. A
herdabilidade estimada para Rmat foi 0,45±0,02,
indicando que o índice é herdável e pode ser
aplicado na seleção para eficiência reprodutiva. A
NP foi o componente de principal variação do RMat.
Touros selecionados com base no RMat
apresentaram filhas mais eficientes