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Journal Article

Perspectivas da avaliação genética multirracial em bovinos no brasil

TL;DR: Os procedimentos de avaliacao genetica multirracial produzem predicoes geneticas aditivas mais acuradas, permitem a comparacao direta de animais de diferente composicao racial e viabilizam o melhoramento genetico aditivo e nao-aditivo em populacoes multirraciais.
Abstract: A disponibilidade de grandes bases de dados em associacoes de diferentes racas e cruzamentos de bovinos,e a demanda crescente dos produtores por avaliacoes geneticas dos animais de racas puras e cruzados tem renovado o interesse na implementacao de procedimentos de avaliacao genetica multirracial. Na maioria das associacoes de criadores dos Estados Unidos esta sendo aplicada a avaliacao genetica de animais puros e cruzados.O Brasil, com sua enorme populacao bovina (167 milhoes),composta amplamente por Zebu e seus cruzamentos (80%),e muitas grandes e bem estruturadas empresas (varias com dez mil animais ou mais), e provavel que possua um expressivo numero de bases de dados apropriadas para ser analisado por meio de procedimentos de avaliacao genetica multirracial. Comumente, no entanto, neste pais sao usados procedimentos de avaliacao genetica intra-racial independentemente da composicao genetica das populacoes bovinas. Os procedimentos intra-raciais ignoram os efeitos geneticos nao-aditivos entre racas, e assumem que os parâmetros geneticos sao os mesmos em todos os grupos raciais. Os procedimentos de avaliacao genetica multirracial incluem ambos os aspectos, assim, eles sao preferiveis aos intra-raciais para avaliar geneticamente populacoes compostas por animais puros e cruzados. Os procedimentos de avaliacao genetica multirracial produzem predicoes geneticas aditivas mais acuradas, permitem a comparacao direta de animais de diferente composicao racial e viabilizam o melhoramento genetico aditivo e nao-aditivo em populacoes multirraciais. No entanto, esses procedimentos sao computacionalmente mais complexos, requerem maior numero de parâmetros geneticos e apresentam problemas de confundimento e multi colinearidade. Neste artigo, caracterizam-se as populacoes multirraciais, discutem-se modelos de avaliacao genetica, procedimentos e tarefas para sua implementacao, e, quando relevante, apresentam-se comentarios gerais sobre a situacao multirracial no Brasil. PALAVRAS-CHAVE: Bovinos, cruzamento, avaliacao genetica, multirracial, predicao.

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Citations
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Journal ArticleDOI
TL;DR: O trabalho foi realizado com o objetivo de avaliar alternativas para a modelagem do efeito da idade da vaca ao parto sobre o peso a desmama of bezerros mesticos Charoles-Zebu.
Abstract: The objective of this study was to evaluate alternatives for modeling the age of dam at calving (AOD) effect on the weaning weight of Charolais-Zebu crossbred calves. Data from 56,965 calves were analyzed, using statistical models considering the fixed effects of the contemporary groups, sire and dam genetic groups, and AOD. The AOD effect was fitted to models using annual age classes, and ordinary quadratic to quintic-ordered polynomials (OP) or segmented polynomials (SP) with two, three, four, six and twelve evenly spaced intervals. In the case of segmented polynomials, general linear and quadratic effects and only one quadratic additional term from each knot were considered. The AOD effects were nested within sex of calf in all cases. According to the fitting criteria, the F-test for the reduction of residual sum of squares, coefficient of determination, residual sum of squares and mean of squared residuals, the three interval segmented polynomial (two knots) fitted to the data as well as the more complex polynomials.

5 citations


Cites background from "Perspectivas da avaliação genética ..."

  • ...…matings of individuals with the same genetic composition and of some crosses, such as the F2, characterized an incomplete multiracial population (Elzo & Borjas, 2004), that can occur because, in this commercial population, the crossings are directed to produce animals with a predetermined…...

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Journal ArticleDOI
TL;DR: The influence of environmental parameters on the physiological responses of purebred and crossbred Nellore calves born in a subtropical region was studied and PT level was significantly higher in NR calves than in NI ones.
Abstract: Estudou-se a influencia de fatores climaticos sobre as respostas fisiologicas de bezerros, puros e cruzados, filhos de vacas da raca Nelore ou de alta mesticagem de Nelore acasaladas com touros das racas Aberdeen Angus (AN), Simental (SN), Canchim (CN) e Nelore (NI e NR). Os bezerros AN, SN, CN e NI foram mantidos em sistema rotacionado intensivo, enquanto o grupo NR foi mantido em sistema extensivo. Os bezerros foram observados de forma direta desde o nascimento ate a primeira mamada, medindo-se a latencia para a primeira mamada (LM). Aproximadamente 24 horas apos o parto, coletaram-se amostras de sangue do bezerro para as dosagens de proteina total (PT), glicose (Gli), triiodotironina (T3), tiroxina (T4), relacao T4:T3, cortisol (Cort) e imunoglobulina G (IgGb), alem das medidas de temperatura retal do bezerro (TR) e dos pesos de vacas e bezerros. Para analise dos efeitos de clima, foram tomadas no dia do nascimento as medidas de temperatura do ar (Temp), umidade do ar (UR) e precipitacao (PRE). Os parâmetros fisiologicos foram estudados pelo metodo dos quadrados minimos com modelos que incluiram os efeitos de ano e mes de nascimento, grupo e sexo do bezerro, categoria da vaca e hora do parto e das interacoes ano × grupo e ano × mes de nascimento, alem das covariaveis peso do bezerro, PRE, Temp, UR e LM. Temp mostrou efeito significativo para as concentracoes de T3, T4, T4:T3 e de Cort. Quanto maior Temp, menores as concentracoes de T3 e de Cort e maiores as de T4 e de T4:T3. LM influenciou os niveis de Cort, PT e IgGb, de modo que, quanto maior LM, maior a concentracao de Cort e menor as de IgGb e PT. Tambem houve efeito significativo de grupo do bezerro sobre PT, que foi maior nos bezerros NR que nos bezerros NI.

2 citations

01 Jun 2011
TL;DR: In this article, the influence of some non-genetic factors on birth (BW) and weaning weight corrected to 205 d (WWA) of Angus calves, 1,999 and 1,574 weights were analyzed.
Abstract: To determine the influence of some non-genetic factors on birth (BW) and weaning weight corrected to 205 d (WWA) of Angus calves, 1,999 and 1,574 weights were analyzed. All the animals were grazing and they were vaccinated against enzootic every six months. The data was analyzed using an analysis of variance under least squares methodology and the statistical model included: year of birth (YB = 1991-2007), season of birth (SB = Cold, Dry and Rainy), parity number (PN = 1, 2, 3,… ≥9 calving) and sex (SX = Males and Females) and the interactions YB*SB, YB*PN and YB*SX. All effects and the interactions affected BW and WWA (P<0,01). The means and standard deviation were 36.2 ± 2.6 and 186.8 ± 30.0 kg, respectively. The differences between the best years (2007) and worse year (1991) to BW was 1.1 kg. Cows of 1, 2 and ≥9 calving had calves less heavy. Male calves weighted more than female to birth and weaning. The interactions that involved YB indicate that the direction and magnitude of the effects are not constant within every year. The interaction YB*SB, YB*PN and YB*SX were important on WWA without being possible to define some tendency or magnitude. All the environmental effect studied was important.

2 citations

Journal Article
TL;DR: Multibreed genetic evaluation models allow the prediction of animal breeding values in a population of animals of various breed compositions to yield additive and nonadditive animal genetic values, which allow more precise selection decisions and mating plans.
Abstract: Multibreed genetic evaluation models allow the prediction of animal breeding values in a population of animals of various breed compositions. The structure of this type of model depends on the traits to be evaluated and the multibreed population to be analyzed, and they eventually yield additive and nonadditive animal genetic values, which allow more precise selection decisions and mating plans.

1 citations

01 Jun 2011
TL;DR: In this article, the influence of some non-genetic factors on birth and weaning weight corrected to 205 d (WWA) of Angus calves, 1,999 and 1,574 weights were analyzed.
Abstract: To determine the influence of some non-genetic factors on birth (BW) and weaning weight corrected to 205 d (WWA) of Angus calves, 1,999 and 1,574 weights were analyzed. All the animals were grazing and they were vaccinated against enzootic every six months. The data was analyzed using an analysis of variance under least squares methodology and the statistical model included: year of birth (YB = 1991-2007), season of birth (SB = Cold, Dry and Rainy), parity number (PN = 1, 2, 3,… ≤9 calving) and sex (SX = Males and Females) and the interactions YB x SB, YB x PN and YB x SX. All effects and the interactions affected BW and WWA (P <0,01). The means and standard deviation were 36.2 ± 2.6 and 186.8 ± 30.0 kg, respectively. The differences between the best years (2007) and worse year (1991) to BW was 1.1 kg. Cows of 1, 2 and ≤9 calving had calves less heavy. Male calves weighted more than female to birth and weaning. The interactions that involved YB indicate that the direction and magnitude of the effects are not constant within every year. The interaction YB x SB, YB x PN and YB x SX were important on WWA without being possible to define some tendency or magnitude. All the environmental effect studied was important.

1 citations

References
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Journal ArticleDOI
TL;DR: The theory presented here can be used to obtain genetic evaluations by best linear unbiased prediction and to estimate genetic parameters by maximum likelihood in a two-breed population under dominance inheritance.
Abstract: This paper presents theory and methods to compute genotypic means and covariances in a two breed population under dominance inheritance, assuming multiple unlinked loci. It is shown that the genotypic mean is a linear function of five location parameters and that the genotypic covariance between relatives is a linear function of 25 dispersion parameters. Recursive procedures are given to compute the necessary identity coefficients. In the absence of inbreeding, the number of parameters for the mean is reduced from five to three and the number for the covariance is reduced from 25 to 12. In a two-breed population, for traits exhibiting dominance, the theory presented here can be used to obtain genetic evaluations by best linear unbiased prediction and to estimate genetic parameters by maximum likelihood.

35 citations

Journal ArticleDOI
TL;DR: Theories de covariance entre apparentes dans les croisements entre 2 populations sont utilisees pour predire les valeurs genetiques par le BLUP-modele animal.
Abstract: Prediction des valeurs genetiques avec des modeles individuels additifs pour des croisements a partir de 2 populations. De recentes avancees de la theorie de la covariance entre apparentes dans les croisements entre 2 populations, en heredite additive, sont utilisees pour predire les valeurs genetiques (VG) par le BLUP-modele animal. Les consequences resultant d'une definition incorrecte de la matrice de covariance des VG sont discutees. La theorie de la covariance entre apparentes en croisement a partir de 2 populations est etendue a la prediction de VG pour plusieurs caracteres. Un exemple numerique illustre les procedures de prediction.

24 citations

Journal ArticleDOI
TL;DR: Number of iterations and computing times to achieve convergence when estimating 21 genetic and environmental covariances in five small simulated multibreed data sets suggest that these procedures are computationally feasible.
Abstract: Restricted maximum-likelihood procedures were developed to estimate additive and nonadditive genetic and environmental covariances for multiple traits in multibreed populations. The computational procedure follows the expectation-maximization (EM) algorithm, where the set of equations in the maximization step is solved by successive approximations. This computational procedure does not guarantee convergence to a symmetric positive-definite covariance matrix. Thus, computer programs will need to incorporate restrictions in the maximization step to ensure positive definiteness of each covariance matrix. Additive genetic and environmental covariances were modeled in subclass form (zeros and ones in the design matrices). Nonadditive genetic covariances were modeled in regression form (any value between and including zero and one in the design matrices). Computational requirements will be larger than for intrabreed analyses. Appropriate simplifying assumptions and numerical techniques (e.g., sparse and iterative numerical techniques) will be required for the implementation of these multibreed covariance estimation procedures. Number of iterations (5 to 12) and computing times (57 to 113 min) to achieve convergence when estimating 21 genetic and environmental covariances in five small simulated multibreed data sets (two breeds, 25,200 to 50,400 calves, 120 to 135 unrelated bulls) suggest that these procedures are computationally feasible.

23 citations

Journal ArticleDOI
TL;DR: The prediction of nonadditive genetic values for bulls, in addition to their additive genetic values, will help plan matings, make selection decisions more accurate and, possibly, make economic projections better.
Abstract: In multibreed populations, bulls need to be evaluated for additive and nonadditive genetic effects. When the nonadditive genetic effects associated with a bull are defined as sire x breed-group-of-dam interactions, they can be expressed as linear combinations of interactions between alleles of one or more breeds at one or more loci. If these specific allelic interactions are assumed to be independent, then variances and covariances between sire x breed-group-of-dam interaction subclasses can be shown to be linear combinations of variances and covariances of specific intra- and interlocus intra- and interbreed allelic interactions. Furthermore, covariances between sire x breed-group-of-dam interactions due to specific interactions at one, two, or more loci are zero. If dams are assumed to be unrelated to bulls and among themselves, except through their sires and maternal grandsires, efficient procedures to compute the inverse of the covariance matrices of nonadditive genetic effects can be devised, both in subclass and in regression models. Recursive procedures developed make possible the evaluation of large numbers of bulls for nonadditive genetic effects using mixed-model methodology. For completeness, recursive procedures to compute nonadditive covariance matrices in subclass and in regression models also were developed. The prediction of nonadditive genetic values for bulls, in addition to their additive genetic values, will help plan matings, make selection decisions more accurate and, possibly, make economic projections better.

22 citations

Journal ArticleDOI
TL;DR: Although the overall accuracy of both procedures was similar, the Cholesky Maximization procedure should be preferred because it converged faster and its covariance estimates were less affected by the values of the covariance priors than those computed using the Partial Scoring strategy.
Abstract: Two unconstrained procedures to ensure that intrabreed and interbreed genetic and environmental covariance estimates for multibreed populations are computed within the permissible ranges were developed. These procedures were called Partial Scoring and Cholesky Maximization. The Partial Scoring procedure uses partial steps to keep estimates of covariance matrices positive definite at each expectation-maximization (EM) iteration, and the Cholesky Maximization procedure achieves the same goal by computing the elements of the Cholesky Decomposition of each intrabreed and interbreed genetic and environmental covariance matrix. Groups of small simulated data sets containing either direct genetic effects of two traits (90 bulls, 13,500 calves) or direct and maternal genetic effects for a single trait (135 bulls, 32,400 calves) were used to test the computational feasibility of these two procedures. The overall means (and ranges) of the numbers of expectation-maximization iterations, times to convergence, and accuracy of estimation were 10 (2 to 184), 26.2 min (4.1 to 773.2 min), and 40.1% (12.7 to 81.9%) for the Partial Scoring procedure and 7 (3 to 37), 16.7 min (9.5 to 64.6 min), and 37.8% (3.1 to 67.8%) for the Cholesky Maximization procedure. Although the overall accuracy of both procedures was similar, the Cholesky Maximization procedure should be preferred because it converged faster and its covariance estimates were less affected by the values of the covariance priors than those computed using the Partial Scoring strategy. Application to large unbalanced multibreed data sets will require an iterative version of these procedures.

20 citations