ABSTRACT. The objective of this study was to develop a bio-economic model for the estimation of economic values of economically important traits in a full-cycle beef cattle production system. The bio-economic model calculated economic values by simulating the impact of changes in the profit of the system consisting of a 1% increase in each trait of the breeding objective, while the other traits were kept constant. The bio-economic model was effective in estimating the sources of revenues and expenses of the production system. The estimated economic values were, in the order of importance for the full-cycle system, R$ 3.69 for male slaughter weight, R$ 3.63 for male weaning weight, R$ 3.58 for weaning rate, R$ 3.40 for female slaughter weight, R$ 2.30 for female weaning weight, and R$ 0.13 for mature cow weight. The results showed that all traits evaluated in the full-cycle system had positive economic impact, indicating that selection would increase profitability maximizing the expected response for the traits of the breeding goal.

ABSTRACT The objectives of this study were to estimate genetic parameters and genetic trends and perform principal component analysis for the following traits: body weight adjusted at 210 days of age (W210), one year (W365), and yearling or 450 days of age (W450); weight gain from birth to weaning or 210 days of age (WGBW), from weaning to 365 days of age (WGW365), and from one year to yearling (WGY); and scrotal circumference adjusted at 365 (SC365) and 450 (SC450) days of age of Guzera beef cattle. Variance components were estimated under a two-trait animal model using the restricted maximum likelihood method. The fixed effects included in the model were birth season, contemporary group, and covariable age of dam at calving as linear and quadratic effects. Heritability estimates ranged from 0.10 (WGY) to 0.41 (W450 and SC450). The studied traits could be used as selection criteria because of their sufficient additive genetic variability to respond to the selection process. However, lower selection efficiency is expected for WGBW and WGY. Genetic trends studied were significant for all traits, except WGY. The W365 and W450 traits belonged to the “Genetic Merit Total” index and responded to selection with favorable genetic gain per year. The traits that were not included in the selection index showed favorable positive genetic correlations attributed to the indirect selection processes. The principal component analysis identified two groups of traits. The first group related to body weight and weight gain and the second related to the scrotal circumference, indicating that selection could be applied to one group of traits within each observed group. The genetic gains were attributed in the same direction for the other traits belonging to the groups. Thus, we recommend selecting animals for W365 based on first group, and SC365 based on second.

A interação genótipo-ambiente (IGA) foi estudada por meio de dois procedimentos distintos, em características produtivas e reprodutivas de bovinos da raça Nelore. Dados de pesos padronizados aos 120 (P120); 210 (P210); 450 (P450) dias de idade, perímetro escrotal aos 450 dias de idade (PE450) e idade ao primeiro parto (IPP), de 211.744 registros de animais Nelore, criados na região da Amazônia Legal, foram utilizados na análise. O efeito da IGA foi estudado por meio de estimativas de herdabilidade e de correlações entre classificações, comparando os animais da Amazônia Legal com a base geral de animais do PMGRN - Nelore Brasil. As análises bi-característica consideraram o P120 como característica-âncora, com P210; P450 e PE450. A característica IPP foi analisada separadamente, em análise de característica única e considerando como efeito fixo o GCIPP e como aleatórios os efeitos aditivos genético e residual. As estimativas de herdabilidade para P120; P210; P450; PE450 e IPP nos dados da Amazônia Legal foram: 0,20 a 0,49; 0,21; 0,48; 0,45 e 0,21, respectivamente, e nos dados gerais do PMGRN - Nelore Brasil foram: 0,23; 0,25; 0,34; 0,43 e 0,11, respectivamente. As correlações entre classificações de rank para P120; P210; P450; PE450 e IPP foram iguais a 0,77; 0,79; 0,82; 0,78 e 0,38, respectivamente. As análises da IGA, por meio das estimativas de herdabilidade, evidenciaram maiores efeitos sobre os aspectos maternos, de peso aos 450 dias de idade e idade ao primeiro parto, enquanto que as correlações entre classificações mostraram fortes evidências em quase todas as características estudadas.

Genotype-environment interaction was studied by two different procedures in productive and reproductive traits of Nellore cattle. Data from adjusted weights at 120 (P120), 210 (P210), 450 (P450) days of age, scrotal circumference at 450 days of age (PE450) and age at first calving (IPP) for 211,744 records from Nellore herds located in the Legal Amazon region were used in the analysis. The effect of genotype-environment interaction was studied through heritability estimates and rank correlation, comparing the Legal Amazon animals with the general basis of animals - PMGRN Nellore Brazil. Bi-trait analyses considered P120 as anchor-trait with P210, P450 and PE450 as another one. IPP has been analyzed separately in single-trait analysis and considering GCIPP as fixed and additive and residual effects as random. Estimates of heritability for P120, P210, P450, PE450 and IPP on the data of the Legal Amazon were: 0.20 to 0.49; 0.21; 0.48; 0.45; and 0.21, respectively, and in general data of PMGRN - Nellore Brazil were: 0.23; 0.25; 0.34; 0.43 and 0.11, respectively. Correlations between rank for P120, P210, P450, PE450 and IPP were equal to 0.77; 0.79; 0.82; 0.78 and 0.38, respectively. The analysis of the genotype-environment interaction, through the heritability estimates, showed larger effects on maternal, weight at 450 days of age and age at first calving, whereas the rank correlations showed strong evidence in almost all traits studied.

A total of 204,912 records of birth weights up to 550 days of age, of 24,890 Nellore cattle, offspring of 375 sires and 16,917 dams from five herds in the state of Mato Grosso, Brazil, were used in order to describe the variability of the weight development by random regression models. The model evaluated as the most suitable used the covariance function of fourth order to describe the variability of the effects of additive genetic, animal permanent environmental and maternal effects of third order to describe the maternal genetic effect, with four classes of residual variance. Heritability estimates ranged from 0.18 to 0.46 from the beginning of trajectory to 210 days of age, from 0.45 to 0.48 post-weaning to 365 days of age and from 0.47 to 0.57 at later ages. The values of additive genetic correlations for different ages showed higher estimates between the closest ages, while birth weight was not very related to the weights at older ages. The body weight performance of the animals has additive genetic variation to respond to selection.

Verificou-se a influência da heterogeneidade de variâncias na avaliação genética de bovinos de corte da raça Nelore. Dados de pesos padronizados aos 365, 450 e 550 dias de idade foram estratificados com base no desvio-padrão fenotípico dos rebanhos para cada peso. Nas análises de múltiplas características, em que o mesmo peso foi considerado característica distinta em cada classe de desvio-padrão, as variâncias genéticas e residuais aumentaram com o desvio-padrão da classe. As estimativas de herdabilidade foram iguais a 0,34 e 0,36; 0,41 e 0,41, 38 e 49 nas classes de alto e baixo desvio-padrão fenotípico para os pesos aos 365, 450 e 550 dias, respectivamente. As correlações genéticas entre o mesmo peso nas classes de baixo e alto desvio-padrão foram iguais a 0,71; 0,80; e 0,84 para os pesos aos 365, 450 e 550 dias, respectivamente. As correlações de Spearman entre os valores genéticos, obtidos de análises múltiplas e de análise geral (sem as classes), e entre o mesmo peso nas classes de desvios-padrão, reduziram à medida que aumentou a intensidade de seleção sobre os reprodutores. A presença de heterogeneidade de variâncias causa maior impacto sobre a avaliação genética dos reprodutores sob intensidade de seleção elevada, sendo interessante sua consideração no processo de avaliação genética.

Data from Nellore beef cattle breed were used to study the influence of variance heterogeneity on genetic evaluation. Adjusted weights at 365, 450 and 550 days of age were classified as high and low classes of standard deviation, based on phenotypic standard deviation of herds in each weight. At multiple trait analyses, where the same weight was considered a distinct characteristic regarding each class of standard deviation, genetic and residual variances increased as the standard deviation of the class increased. Genetic correlations between the same weight, in high and low phenotypic standard deviation classes were 0.71, 0.80 and 0.84 for weights at 365, 450 and 550 days, respectively. Spearman correlations between breeding values obtained from multiple trait analyses and general analysis (without classes), and between classes of standard deviations, lowered as the intensity of selection on sires increased. The presence of heterogeneity of variances has greater impact on the genetic evaluation of breeding under high intensity of selection, it is interesting your consideration in the process of genetic evaluation.

Objetivou-se com este trabalho utilizar regras de associação para identificar forças de mercado que regem a comercialização de touros com avaliação genética pelo programa Nelore Brasil. Essas regras permitem evidenciar padrões implícitos nas transações de grandes bases de dados, indicando causas e efeitos determinantes da oferta e comercialização de touros. Na análise foram considerados 19.736 registros de touros comercializados, 17 fazendas e 15 atributos referentes às diferenças esperadas nas progênies dos reprodutores, local e época da venda. Utilizou-se um sistema com interface gráfica usuário-dirigido que permite geração e seleção interativa de regras de associação. Análise de Pareto foi aplicada para as três medidas objetivas (suporte, confiança e lift) que acompanham cada uma das regras de associação, para validação das mesmas. Foram geradas 2.667 regras de associação, 164 consideradas úteis pelo usuário e 107 válidas para lift ≥ 1,0505. As fazendas participantes do programa Nelore Brasil apresentam especializações na oferta de touros, segundo características para habilidade materna, ganho de peso, fertilidade, precocidade sexual, longevidade, rendimento e terminação de carcaça. Os perfis genéticos dos touros são diferentes para as variedades padrão e mocho. Algumas regiões brasileiras são nichos de mercado para touros sem registro genealógico. A análise de evolução de mercado sugere que o mérito genético total, índice oficial do programa Nelore Brasil, tornou-se um importante índice para comercialização dos touros. Com o uso das regras de associação, foi possível descobrir forças do mercado e identificar combinações de atributos genéticos, geográficos e temporais que determinam a comercialização de touros no programa Nelore Brasil.

The aim of this work was to use association rules to identify forces that govern bull trade with genetic evaluation by Programa Nelore Brasil. Those rules permit to highlight patterns implicit in the transactions of large databases, which indicate determining causes and effects of supply and trade of bulls. In the analysis, it was considered 19,736 records of traded bulls, 17 farms and 15 attributes related to expected differences on the progenies of sires, place and time of sale. A system with user-driven graphical interface that allows generation and interactive selection of association rules was used. Pareto analysis was applied for the three objective measures (support, trust and lift) that follow each one of the association rules to validate them. It was generated 2,667 association rules, 164 considered to be useful by the user and 107 valid for lift ≥ 1.0505. The farms participating in the Nelore Brasil program present expertise in bull offering according to maternal ability characteristics, weight gain, fertility, sexual precocity, longevity, yield and termination of carcass. The genetic profiles of the bulls are different for standard and Mocho Nellore varieties. Some Brazilian regions are market niche for sires without registered herd. The analysis of evolution of the market suggests that Mérito Genético Total (MGT), the official index of the Program Nelore Brasil has become an important index for commercialization of bulls. By using association rules, it was possible to discover market forces and to identify combinations of genetic, geographical and temporal attributes that determine commercialization of bulls in Nelore Brasil program.

O objetivo neste estudo foi estimar as correlações genéticas entre escores visuais e características de carcaça medidas por ultrassonografia em bovinos da raça Nelore utilizando a estatística bayesiana por meio da Amostragem de Gibbs, sob modelo animal linear-limiar. Foram estudadas as características categóricas morfológicas de musculosidade, estrutura física, conformação e sacro, avaliadas aos 15 e 22 meses de idade. Para as características de carcaça, foram avaliadas as características área de olho-de-lombo, espessura de gordura subcutânea, espessura de gordura subcutânea na garupa e altura na garupa. Os escores visuais devem ser empregados como critérios de seleção para aumentar o progresso genético para a característica área de olhode-lombo e, consequentemente, melhorar o rendimento de carcaça. As estimativas de correlação genética obtidas para musculosidade com espessura de gordura subcutânea e espessura de gordura subcutânea na garupa indicaram que a seleção para musculosidade pode levar a animais com melhor acabamento de carcaça. A seleção para a estrutura física e conformação aos 15 e 22 meses de idade pode promover resposta correlacionada para o aumento da altura na garupa.

The objective of this study was to estimate the genetic correlations between visual scores and the carcass traits measured by ultrasound, in Nellore breed cattle, using the bayesian statistics by Gibbs Sampling, in the linear-threshold model. The morphological categorical traits of musculature, physical structure, conformation and sacrum were studied, evaluated at 15 and 22 months. The carcass traits of the longissimus muscle area, backfat thickness, rump fat thickness and hip height were evaluated. Visual scores should be used as selection criterion to increase genetic progress for the longissumus muscle area. The estimates of genetic correlations obtained between musculature and backfat thickness and rump fat thickness indicated that the selection for musculature may lead to animals with better carcass finishing. Selection for physical structure and conformation, at 15 and 22 months, should promote response correlated with the hip height.

Os objetivos neste estudo foram estimar parâmetros genéticos das características categóricas musculosidade, estrutura física, aspectos raciais, conformação, ônfalo, pigmentação e sacro e predizer os valores genéticos utilizando-se a estatística bayesiana sob modelo animal de limiar, considerando diferentes idades de bovinos da raça Nelore. As informações de escores visuais foram obtidas nos anos de 2000 a 2005 de bovinos provenientes de 13 fazendas participantes do Programa Nelore Brasil. Nas análises bicaracterísticas, foram utilizados 500.000 até 1.100.000 ciclos para alcançar a convergência da cadeia de Gibbs. O descarte inicial e o intervalo amostral foram de 100.000 e 1.000 ciclos, respectivamente. As características de escores visuais avaliadas aos 8 e 22 meses de idade apresentaram estimativas de herdabilidades moderadas, indicando resposta rápida à seleção direta. Os escores visuais indicaram possibilidade de resposta rápida à seleção direta e, portanto, devem ser incorporados em programas de melhoramento genético como critérios de seleção. As estimativas de correlações genéticas entre musculosidade, estrutura física e conformação também indicam que a seleção direta para uma destas características trará progresso genético às outras. Recomenda-se utilizar os escores visuais como critérios de seleção em pelo menos duas fases de vida do animal, na desmama e ao sobreano.

The objectives of this study were to estimate the genetic parameters of the following categorical traits: musculature, physical structure, racial breed aspects, conformation, navel, pigmentation and sacrum, and predict breeding values, using bayesian statistics under threshold animal models, considering different ages of cattle of the Nelore breed. The information concerning visual scores were obtained from 2000 to 2005 from cattle of the Nelore breed from thirteen participant farms of the Brazilian Nelore Program. In the two-trait analyses, 500,000 rounds up to 1,100,000 cycles were used to reach the convergence of the Gibbs chain. The burn-in and thinning interval were 100,000 and 1,000 cycles, respectively. The evaluated visual scores at the age of 8 and 22 months presented moderate heritability estimates, suggesting that these traits can be used to promote genetic gain by direct selection. The genetic correlations between the morphological traits of musculature, physical structure and conformation were moderate, indicating correlated responses between the traits. The use of the visual scores is recommended, as selection criteria, in at least two phases of the animal life, at weaning and yearling time.

The aim of this study was to estimate the components of variance and genetic parameters for the visual scores which constitute the Morphological Evaluation System (MES), such as body structure (S), precocity (P) and musculature (M) in Nellore beef-cattle at the weaning and yearling stages, by using threshold Bayesian models. The information used for this was gleaned from visual scores of 5,407 animals evaluated at the weaning and 2,649 at the yearling stages. The genetic parameters for visual score traits were estimated through two-trait analysis, using the threshold animal model, with Bayesian statistics methodology and MTGSAM (Multiple Trait Gibbs Sampler for Animal Models) threshold software. Heritability estimates for S, P and M were 0.68, 0.65 and 0.62 (at weaning) and 0.44, 0.38 and 0.32 (at the yearling stage), respectively. Heritability estimates for S, P and M were found to be high, and so it is expected that these traits should respond favorably to direct selection. The visual scores evaluated at the weaning and yearling stages might be used in the composition of new selection indexes, as they presented sufficient genetic variability to promote genetic progress in such morphological traits.

O objetivo deste trabalho foi comparar as estimativas de parâmetros genéticos obtidas em análises bayesianas uni-característica e bi-característica, em modelo animal linear e de limiar, considerando-se as características categóricas morfológicas de bovinos da raça Nelore. Os dados de musculosidade, estrutura física e conformação foram obtidos entre 2000 e 2005, em 3.864 animais de 13 fazendas participantes do Programa Nelore Brasil. Foram realizadas análises bayesianas uni e bi-características, em modelos de limiar e linear. De modo geral, os modelos de limiar e linear foram eficientes na estimação dos parâmetros genéticos para escores visuais em análises bayesianas uni-características. Nas análises bi-características, observou-se que: com utilização de dados contínuos e categóricos, o modelo de limiar proporcionou estimativas de correlação genética de maior magnitude do que aquelas do modelo linear; e com o uso de dados categóricos, as estimativas de herdabilidade foram semelhantes. A vantagem do modelo linear foi o menor tempo gasto no processamento das análises. Na avaliação genética de animais para escores visuais, o uso do modelo de limiar ou linear não influenciou a classificação dos animais, quanto aos valores genéticos preditos, o que indica que ambos os modelos podem ser utilizados em programas de melhoramento genético.

The objective of this work was to compare the estimates of genetic parameters obtained in single-trait and two-trait bayesian analyses, under linear and threshold animal models, considering categorical morphological traits of bovines of the Nelore breed. Data of musculature, physical structure and conformation were obtained between years 2000 and 2005, from 3,864 bovines of the Nelore breed from 13 participant farms of the Nelore Brazil Program. Single-trait and two-trait bayesian analyses were performed under linear and threshold animal models. In general, the linear and threshold models were efficient in estimating genetic parameters for visual scores under single-trait bayesian analyses. In the two-trait analyses, it was observed that: using continuous and categorical data, the threshold model provided greater estimates of genetic correlation than those of the linear model; with categorical data, the heritability estimates were similar. One major advantage of the linear models was its smaller requirements in the analyses processing time. In the genetic evaluation of animals for visual scores, the use of the linear or threshold model did not influence the classification of the animals, based on their predicted breeding values, which suggests that both models can be used in genetic improvement programs.

Com objetivo de estimar parâmetros genéticos e estudar a utilização de diferentes efeitos em avaliações genéticas para idade ao primeiro parto (IPP) por diferentes modelos, foram utilizados registros de IPP de animais da raça Nelore, nascidos entre os anos de 1990 e 2005. Foram considerados os seguintes modelos (M): M1, incluindo o efeito fixo de GC1 (constituído pelos animais nascidos na mesma fazenda e ano), além da covariável, peso aos 365 dias de idade (efeito linear e quadrático), totalizando 24.263 registros de IPP; M2, considerando os efeitos fixos de GC1, ano e estação de parição, totalizando 59.792 registros de IPP e M3, incluindo os efeitos fixos de GC2 (agrupando os animais nascidos na mesma fazenda, ano e que conceberam no mesmo manejo reprodutivo), ano e estação de parição, totalizando 59.792 registros de IPP. As estimativas dos componentes de variância e herdabilidade e os valores genéticos (VG) foram obtidos pelo método da máxima verossimilhança restrita, com a inclusão da matriz de parentesco disponível. As diferenças esperadas na progênie (DEPs) foram obtidas dividindo os VG por dois. Após a obtenção desses resultados, foram realizadas correlações entre os VG e o ranqueamento das DEPs dos reprodutores para IPP, utilizando-se o procedimento PROC CORR (SAS, 2003). Ao se considerar o ano e a estação de parto nos modelos de análise (M2 e M3), esses produziram um maior R², indicando que tais modelos conseguiram explicar, em maior grau, as diferenças existentes entre os animais para IPP. As herdabilidades estimadas foram de baixa magnitude (0,14 e 0,15). As correlações entre os VG obtidas por diferentes modelos foram 0,73 (M1 x M2); 0,91 (M2 x M3) e 0,66 (M1 x M3).

With the objective of estimate genetic parameters and study the utilization of different effects on the genetic evolution for the age of the first calving (AFC) by different models, they were used AFC records from Nellore breed animals, born from 1990 to 2005. They were considered the following models (M): M1, including the fixed effect of the contemporary group (CG), CG1 (grouping the animals that were born at the same farm and year), besides the co variable, weight at 365 days of age (linear and quadratic effects), totalizing 24,263 records of AFC; M2, considering the effects of CG1, year and season of the calving, totalizing 59,792 records of AFC and M3, including effects CG2 (grouping the animals born at the same farm, year and submitted at the same reproductive management), year and season of calving totalizing 59,792 records of AFC. The components of variance and Genetic Value (GV) were obtained by Restricted Maximun Likelihood Method, with the inclusion for the relationship matrix. The Differences Expected on the Progeny (DEPs) were obtained by dividing the GV by two, after this they were estimated the correlations between GV and ranks of the reproductor's DEPs for AFC, utilizing the procedure CORR (SAS, 2003). While considering year and season of calving in the analysis models (M2 and M3), it was produced a bigger R², indicating that those models could explain, in a larger scale, the existing differences between the animals for AFC. The heritabilities estimated were of low magnitude (0,14 and 0,15). The correlations between the GV obtained by the different models were .73 (M1 x M2); .91 (M2 x M3) and .66 (M1 x M3).

Visando estimar parâmetros genéticos em bovinos, foram utilizados registros de pesos padronizados aos 120, 210, 365, 450 e 550 dias de idade (P120, P210, P365, P450 e P550), altura do posterior mensurada próxima ao sobreano (ALT) e circunferências escrotais (CE) padronizadas aos 365, 450 e 550 dias de idade (CE365, CE450 e CE550). Os dados foram provenientes de animais machos e fêmeas, nascidos entre 1998 e 2003 em dez fazendas de seis estados brasileiros. Os componentes de (co)variância foram estimados pela metodologia REML em análises uni, bi e trivariadas, utilizando-se modelos animal. As estimativas de herdabilidade do efeito direto com os respectivos erros-padrão foram: ALT 0,63 (0,09), P120 0,25 (0,03), P210 0,34 (0,03), P365 0,45 (0,04), P450 0,48 (0,04), P550 0,49 (0,04), CE365 0,48 (0,04), CE450 0,53 (0,04) e CE550 0,42 (0,09). As correlações genéticas entre a ALT e as variáveis P120, P210, P365, P450 e P550 foram de 0,68; 0,64; 0,53; 0,58 e 0,59, respectivamente. As associações genéticas do P120 com as CE ajustadas para peso e idade foram próximas de zero, entretanto, essas correlações foram positivas e moderadas, quando as CE foram ajustadas somente pela idade. As correlações genéticas da ALT com as CE, quando ajustadas para peso e idade, foram: -0,19 (CE365), -0,24 (CE450) e 0,00 (CE550). Utilizando um modelo que não incluiu o peso do animal como covariável, as correlações genéticas das CE com a ALT foram: 0,21 (CE365), 0,12 (CE450) e 0,39 (CE550). Essas estimativas indicam que as características de crescimento e CE apresentam variabilidade genética na raça Nelore, podendo ser incluídas em programas de melhoramento genético, e a seleção para peso em qualquer idade deve acarretar aumento na estatura dos animais. Desta forma, para obtenção de animais com tamanho e peso adequados ao sistema de produção, faz-se necessária a utilização de um índice de seleção aliando estas características.

Data consisting of standardized weights at 120, 210, 365, 450 and 550 days of age (W120, W210, W365, W450 and W550), hip height at 18 months of age (HH) and standardized scrotal circumferences (SC) at 365, 450 and 550 days of age (SC365, SC450 and SC550) of Nelore animals born between 1998 and 2003, from ten ranches in six Brazilian States were used to estimate (co)variance components. Analyses were done by Restricted Maximum Likelihood methodology using single trait, two and three traits animal models. Heritability estimates of the direct effect for each trait and respective standard errors were: HH 0.63 (0.09), W120 0.25 (0.03), W210 0.34 (0.03), W365 0.45 (0.04), W450 0.48 (0.04), W550 0.49 (0.04), SC365 0.48 (0.04), SC450 0.53 (0.04) and SC550 0.42 (0.09). Genetic correlation estimates between HH and W120, W210, W365, W450, W550 were respectively 0.68, 0.64, 0.53, 0.58 and 0.59. Genetic correlations between W120 and SC adjusted for weight and age were close to zero, but positive and moderate when SC was adjusted only for age. Estimates of genetic correlation between HH and SC adjusted for weight and age were -0.19 (SC365), -0.24 (SC450) and 0.00 (SC550). The same parameter estimates when SC was adjusted only for age were 0.21 (SC365), 0.12 (SC450) and 0.39 (SC550). These results indicate genetic variability for growth traits and SC. Selection for weight at any age will increase stature. In order to obtain Nelore cattle with stature and weight suitable to the production system, both traits should be included in a selection index.

We used Gibbs sampling in single and two-trait animal models to estimate genetic parameters for some reproductive and related traits of Nellore cattle (Bos indicus). Female traits were age at first calving (AFC), cumulative productivity (CP) and adult weight (AW). For males, scrotal circumferences at 365 and 450 days of age were analyzed. Gibbs sampling using the ‘Multiple Trait using Gibbs Sampling under Animal Model’ (MTGSAM) program of Van Tassel and Van Vleck was used to estimate the (co)variance components of the traits and conduct genetic analyses. Heritabilities were AFC = 0.26, AW = 0.36 and CP = 0.25 under the single-trait animal model. The mean, mode and median estimates for genetic parameters obtained from the marginal posterior distributions were similar for all traits except AW, which presented lower values for the mode than the mean and median. However, the marginal posterior distributions for the traits studied presented a tendency toward normality. Favorable, but low, negative genetic correlations were found between male scrotal circumference and female age at first calving. The reproductive traits showed medium-magnitude heritabilities, which indicates that these traits should respond to selection and therefore should be included in genetic improvement programs.

The objective of this study was to estimate (co)variance components and genetic parameters for weights (W) and scrotal circumferences (SC) at 365 and 450 days of age, of Nelore (Bos indicus) cattle, using Bayesian inference in single and multiple-trait animal models. The fitted linear models included, besides the animal and residual random effects, the contemporary group (herd-year-season-sex-management group) and age-of-dam as "fixed effects". The analyses were carried out using a Gibbs sampler implemented through the MTGSAM program. The heritabilities (in parentheses) obtained fitting single-trait models were W365 (0.49), W450 (0.52), SC365 (0.68) and SC450 (0.66). Estimates of means, modes and medians for genetic parameters obtained from marginal posterior distributions were similar for all traits. The W365 and SC365 can be considered as suitable traits to be included as selection criteria in genetic improvement programs, not only because of their relatively high heritabilities but also due to the fact that they can be measured when the animals are relatively young compared to the corresponding traits W450 and SC450. The Bayesian approach appears to be an appropriate alternative for estimating genetic parameters, and has the advantage over point estimation methods of allowing inferences on marginal posterior distributions.

Parameters based on the probability of gene origin were used to describe the genetic variability in strains of Nellore and polled Nellore (Bos indicus) cattle that participated in the Program for Genetic Improvement of the Nellore Breed (Programa de Melhoramento Genético da Raça Nelore). The effective number of founders was 87.2 for Nellore and 107.9 for polled Nellore, while the number of ancestors was 59.8 for Nellore and 61.5 for polled Nellore and the remaining genomes were 39.4 for Nellore and 34.5 for polled Nellore cattle. The results indicate an intense use (by artificial insemination) of some sires and the absence of subdivisions in the population. The family structure in the two breeds was mainly caused by the genetic contribution of the same sires and only mating preferences for descendants of some founders are recorded in either breed. The results suggest that genetic variability needs monitoring in order to avoid the compromise of genetic improvement in economically important traits in the breeding program.