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Journal Article

Perspectivas da avaliação genética multirracial em bovinos no brasil

27 Oct 2006-Ciência Animal Brasileira-Vol. 5, Iss: 4, pp 171-185

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.

AbstractA 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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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
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
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
01 Nov 1981-Genetics
TL;DR: The minimum number of genes involved in producing a large difference between populations in a quantitative trait is typically estimated to be about 5 or 10, with occasional values up to 20, which strongly supports the neo-Darwinian theory that large evolutionary changes usually occur by the accumulation of multiple genetic factors with relatively small effects.
Abstract: A procedure is outlined for estimating the minimum number of freely segregating genetic factors, nE, contributing to the difference in a quantitative character between two populations that have diverged by artificial or natural selection. If certain simple criteria are satisfied approximately on an appropriate scale of measurement, nE can be estimated by comparing the phenotypic means and variances in the two parental populations and in their F1 and F2 hybrids (and backcrosses). This generalizes the method of Wright to genetically heterogeneous (or wild) parental populations, as well as inbred lines. Standard errors of the estimates are derived for large samples. The minimum number of genes involved in producing a large difference between populations in a quantitative trait is typically estimated to be about 5 or 10, with occasional values up to 20. This strongly supports the neo-Darwinian theory that large evolutionary changes usually occur by the accumulation of multiple genetic factors with relatively small effects.

588 citations



Journal ArticleDOI
TL;DR: The inverse of the genotypic covariance matrix given here can be used both to obtain genetic evaluations by best linear unbiased prediction and to estimate genetic parameters by maximum likelihood in multibreed populations.
Abstract: Covariance between relatives in a multibreed population was derived for an additive model with multiple unlinked loci. An efficient algorithm to compute the inverse of the additive genetic covariance matrix is given. For an additive model, the variance for a crossbred individual is a function of the additive variances for the pure breeds, the covariance between parents, and segregation variances. Provided that the variance of a crossbred individual is computed as presented here, the covariance between crossbred relatives can be computed using formulae for purebred populations. For additive traits the inverse of the genotypic covariance matrix given here can be used both to obtain genetic evaluations by best linear unbiased prediction and to estimate genetic parameters by maximum likelihood in multibreed populations. For nonadditive traits, the procedure currently used to analyze multibreed data can be improved using the theory presented here to compute additive covariances together with a suitable approximation for nonadditive covariances.

76 citations


Journal ArticleDOI
TL;DR: The results showed that it is feasible to evaluate sires for additive and nonadditive genetic effects in a structured multibreed population and data from purebred breeders and commercial producers will be needed to accomplish the same goal at a national level.
Abstract: Estimates of covariances and sire expected progeny differences of additive and nonadditive direct and maternal genetic effects for birth and weaning weights were obtained using records from 1,581 straightbred and crossbred calves from the Angus-Brahman multibreed herd at the University of Florida. Covariances were estimated by Restricted Maximum Likelihood, using a Generalized Expectation-Maximization algorithm applied to multibreed populations. Estimates of heritabilities and additive genetic correlations for straightbred and crossbred groups were within the ranges of values found in the literature for these traits. Maximum values of interactibilities (ratios of nonadditive genetic variances to phenotypic variances) and nonadditive correlations were somewhat smaller than heritabilities and additive genetic correlations. Sire additive and total direct and maternal genetic predictions for birth and weaning weight tended to increase with the fraction of Brahman alleles, whereas nonadditive direct and maternal genetic predictions were similar for sires of all Angus and Brahman fractions. These results showed that it is feasible to evaluate sires for additive and nonadditive genetic effects in a structured multibreed population. Data from purebred breeders and commercial producers will be needed to accomplish the same goal at a national level.

76 citations