Abstract The objective of this work was to propose a new stopping criterion to shorten the computing time of the PampaPlus genetic improvement software, while maximizing the genetic qualification index (GQI) of the progeny, controlling inbreeding, and avoiding unintended culling. Data from two beef-cattle herds integrating PampaPlus were used. Five mating scenarios were built using different numbers of sires (9 to 37) and dams (142 to 568). The analyzed algorithm inputs were: expected progeny differences, pedigree information, maximum inbreeding, maximum and minimum number of matches for each sire, and penalty weights for poor performance. The analyzed response variables were computing time and the GQI of the progenies. Three stopping criteria were used: original stopping criterion fixed at 1,000 iterations; saturation stopping criterion (SSC), based on GQI variance; and Bhandari’s stopping criterion (BSC), which includes the generation interval parameter. SSC and BSC reduced processing time in 24.43-53.64% and in 14.32-50.87%, respectively. BSC reaches solution in less time, without losses in GQI quality. BSC is generalizable and effective to reduce the processing time of mating recommendations.

Resumo O objetivo deste trabalho foi propor um novo critério de parada para diminuir o tempo de processamento do programa de melhoramento genético PampaPlus, além de maximizar o índice de qualificação genética (GQI) da progênie, controlar a endogamia e evitar o descarte não intencional. Foram utilizados dados de dois rebanhos integrantes do PampaPlus. Cinco cenários de acasalamento foram elaborados com diferentes números de touros (9 a 37) e vacas (142 a 568). Os dados analisados foram: diferenças esperadas na progênie, informações de pedigree, máxima endogamia, número máximo e mínimo de acasalamentos por touro, e penalidades para desempenho inferior. As variáveis analisadas foram tempo de processamento e o GQI das progênies. Foram utilizados três critérios de parada: critério de parada original, fixado em 1.000 iterações; critério de parada por saturação (SSC), baseado na variância do GQI; e critério de parada de Bhandari (BSC), que inclui o parâmetro de intervalo de gerações. O SSC e o BSC reduziram o tempo de processamento em 24,43-53,64% e em 14,32-50,87%, respectivamente. O BSC atinge solução em menos tempo, sem perda da qualidade do GQI. O BSC é generalizável e efetivo em reduzir o tempo de processamento das recomendações de acasalamento.

Abstract The objective of this study was to evaluate the genetic diversity of Moraxella bovis and Moraxella bovoculi bacteria isolated from infectious bovine keratoconjunctivitis (IBK) outbreaks in the state of Rio Grande do Sul, Brazil. The genetic diversity among Moraxella spp. was evaluated by RAPD-PCR, JWP1-JWOPA07-PCR, ERIC-PCR and by sequencing the 16S-23S intergenic regions. Based on the dendrogram, two genetically differentiated clades were observed; 14 isolates were classified as M. bovis and 17 as M. bovoculi. Genetic distances between the M. bovis samples ranged from 0.0379 to 0.4285, while for M. bovoculi the dissimilarities ranged from zero to 0.7297. Alternatively, based on sequencing analyses of the 16S-23S intergenic region, M. bovis and M. bovoculi isolates were grouped into the same two different clades, but it was not possible to differentiate between isolates within clades. PCR techniques were demonstrated to be a satisfactory tool to unravel the genetic variability among Moraxella spp., while sequencing of the 16S-23S intergenic region was only able to differentiate two species of the Moraxella genus. Despite sampling geographically close regions, we demonstrate considerable genetic diversity in M. bovis and M. bovoculi strains and genetically distinct M. bovis strains co-infecting the same animal.

ABSTRACT Two hundred seventeen grass-finished Braford steers were assessed by ultrasonic scanning and subsequently harvested with their pistol hindquarters fabricated into boneless wholesale cuts. The Longissimus thoracis muscle area and subcutaneous fat depths were measured. The objectives of this study were: 1) to develop prediction equations for weights of the pistol hindquarter and high-value commercial cuts, and 2) to estimate sample size needed for experiments comparing pistol hindquarter retail product weight using either physically or ultrasonically measured carcass traits. Carcass measurements explained 44 % to 94 % of the variation in weights of individual cuts, whereas, measurements that were made using ultrasound explained 42 % to 90 % of the variation in the weights. Models used to predict the weight of pistol hindquarter retail product with carcass measures and ultrasound measures showed high coefficient of determination (R 2 = 0.92 and 0.97, respectively). Whether based on carcass or ultrasound measures, models used to estimate weight percentage of fat trimmed from the pistol hindquarter had lack of fit. In general, models for individual cuts weights that used traits measured with ultrasound as independent variables approached the accuracy of models using carcass traits. Thus, only slightly greater samples sizes were required to have equivalent power to detect differences in retail product weights using ultrasound measures. For experiments of equivalent power, differences in the number of animals required may be offset by avoiding costs for slaughter and fabrication.

ABSTRACT We aimed to evaluate the impact of using embryo transfer (ET) information on weaning weight estimated breeding values (EBV) and its accuracy. Data from Hereford and Braford cattle, raised under extensive conditions in Southern Brazil, were used. A model that included ET information in addition to maternal (genetic and permanent environmental) effects as a function of foster dams was compared to a model without ET information. Accuracy of both bulls and calves increased due to inclusion of ET records in 0.04 and 0.12 points, respectively. In general, the inclusion of ET records provided a greater amount of phenotypic variance and most accurate EBV for sires and progeny. The results obtained in this study encourage the use of ET phenotypic records in large-scale genetic evaluation programs, especially for bulls that have most of their progeny coming from ET. Most of the Brazilian genetic evaluation programs do not use phenotypic records of ET animals. Therefore, breeding values are predicted based only on parentage average, which implies in underestimated accuracies. Considering that ET has been widely used in Brazil and that such information improves genetic predictions, we suggest modifying the traditional adopted models by considering ET information in the Brazilian genetic evaluations.

The objective of this study was to evaluate the genotype-environment interaction (GEI) in the body weight adjusted to 550 days of age (W550) of Polled Nellore cattle raised in Northeastern Brazil using reaction norms (RN) models. Hierarchical RN models included fixed effects for age of cow (linear and quadratic) and random effects for contemporary groups (CG) and additive genetic RN level and slope. Four RN hierarchical models (RNHM) were used. The RNHM2S uses the solutions of contemporary groups estimated by the standard animal model (AM) and considers them as environmental level for predicting the reaction norms and the RNHM1S, which jointly estimate these two sets of unknowns. Two versions were considered for both models, one with a homogeneous (Hm) and another with a heterogeneous (He) residual variance. The one-step homogeneous residual variance model (RNHM1SHm) offered better adjustment to the data when compared with other models. For the RNHM1SHm model, estimates of additive genetic variance and heritability increased with environment improvement (260.75±75.80 kg2 to 4298.39±356.56 kg2 and 0.22±0.05 to 0.82±0.01, for low- and high-performance environments, respectively). High correlation (0.97±0.01) between the intercept and the slope of RN shows that animals with higher genetic values respond better to environment improvement. In the evaluation of breeding sires with higher genetic values in the various environments using Spearman's correlation, values between 0 and 0.98 were observed, pointing to high reclassification, especially among genetic values obtained by the animal model in comparison with those obtained via RNHM1SHm. The existence of GEI is confirmed, and so is the need for specific evaluations for low, medium and high level production environments.

O objetivo deste trabalho foi avaliar a interação genótipo × ambiente (IGA) quanto ao peso ajustado aos 365 dias de idade, em bovinos da raça Nelore Mocha do Nordeste do Brasil, por meio de modelos de norma de reação, via regressão aleatória com abordagem bayesiana. Os modelos analisados incluíram o efeito fixo de idade da vaca (linear e quadrático) e os efeitos aleatórios genético aditivo e de grupo de contemporâneos. O modelo de norma de reação com variância residual homogênea e um passo (MHNRHO1P) proporcionou melhor ajuste aos dados do que os modelos com variância residual heterogênea e o modelo animal padrão (MA). As estimativas de variância genética (64,41±13,24 kg² a 842,31±58,29 kg²) e herdabilidade (0,11±0,01 a 0,63±0,02) aumentaram com a melhoria do gradiente ambiental. As correlações de Spearman variaram de 0,69 a 0,99, entre as classificações dos reprodutores com maiores valores genéticos nos MA e MHNRHO1P, nos diferentes ambientes, o que indica alteração na classificação, especialmente dos valores genéticos obtidos pelo MA nos ambientes superiores. A identificação desse nível de IGA torna necessárias as avaliações específicas dos indivíduos e rebanhos para os ambientes de baixo, médio e alto nível de produção.

The objective of this work was to evaluate the genotype × environment interaction (GEI), for the adjusted weight at 365 days of age, in Polled Nellore cattle from Northeastern Brazil, by using reaction norm models through random regression in a Bayesian approach. The analyzed models included the fixed effect of cow's age (linear and quadratic), and the genetic additive and contemporary group random effects. The one-step reaction norm models with homogeneous residual variance (RNHM1sHm) yielded better data adjustments than the models with heterogeneous residual variance, and the standard animal model (AM). The estimates of genetic variance (64.41±13.24 kg² to 842.31±58.29 kg²) and heritability (0.11±0.01 to 0.63±0.02) increased as the environmental gradient improved. Spearman correlation values ranged from 0.69 to 0.99, among the classification of breeders with the highest breeding genetic values in AM and RNHM1sHm, in distinct environments, indicating changes in classification, particularly in the genetic values obtained by AM in high-quality environments. The identification of such degree of GEI requires that specific evaluation of individuals and herds are performed for environments of low, medium and high production.

The objective of the present study was to analyze models with genetic and/or residual heteroskedasticity for genetic evaluation of the weaning weight of Charolais-Zebu crossbred calves. Weaning weight data from 56,965 crossbred calves were analyzed using animal models with different combinations of genetic and residual heteroskedasticity and/or homoskedasticity. The inference on a posteriori distributions of genetic parameters were by the Monte Carlo method via Markov chains. The model with genetic and residual heteroskedasticity was the best fit on the data. Groups of animals with different genetic compositions, expressed as percentages of Charolais-Zebu breed alleles and individual and maternal heterozygosis, had different genetic variances. These genetic variances could be modeled by linear functions of the Charolais and Zebu genetic variances and the variance attributed to segregation. The breed compositions, the individual and maternal heterozygosis, the sex and age of dam at calving were significant sources of residual heteroskedasticity. The a posteriori means for heritabilities and sire and dam classifications were altered due to genetic and residual heteroskedasticity.

The present study was conducted to assess carcass features, physicochemical and sensory parameters of meat from steers finished on three types of pastures: natural pasture; natural pasture improved, fertilized and oversown with winter species; and annual summer grassland. The experiment was conducted from December 14, 2009 to November 30, 2010, with treatments distributed in a completely randomized design with a different number of replicates. Animals were used as experimental units. Experimental animals were Aberdeen Angus steers with twenty months of initial age and 354±27.4 kg of live weight, on average. The highest average daily gains were obtained for the annual summer grassland. There was no effect of treatments on carcass conformation. The highest carcass yield was obtained on the improved natural pasture. Forequarter yield, side cut yield and longissimus muscle area were similar between the pastures. Moisture and total lipids were not affected by the pasture. Thawing and cooking losses were higher in improved natural pasture and lower in sorghum pasture. Regardless of the treatment, the meat had luminosity ranging from intermediate to dark, high in red, high in yellow, and considered within the normal range for beef. Meat of higher shear force was found in natural pasture, and lower shear force was observed in meat from annual summer grassland. Average live weight daily gain explained 18% of the shear force. Sensory evaluation by duo-trio test showed differences between samples from distinct pastures in flavor. All the studied systems allow for desirable characteristics in carcass and meat.

The objectives of this study were to define breeding objectives and derive economic weights for production traits in family-based beef cattle systems, assess the sensitivity of these weights to changes in market and husbandry indicators and estimate the expected genetic changes in the selection criteria proposed. Based on data from the production systems, farms revenues and expenses, obtained from interviews and meetings with producers, a bioeconomic model was derived, relating biological traits of animals with the financial result of the production system based on calf-crop, selling male calves and culling cows for finishing. Traits considered in the model as breeding goals were weaning rate, weaning weight and cow weight. The economic weights, obtained by the partial derivative of the bioeconomic model with respect to the trait in question, assessed on the average value of the remaining traits, were R$ 73.21% for weaning rate, R$ 17.07/kg for weaning weight and R$ 4.75/kg for cow weight. An index for joint selection of these three criteria would allocate 89.5% of importance to weaning rate, 6.9% for weaning weight and 3.6% for cow weight. In this way, for every R$ 100.00 of genetic gain in this index, there would be an increase of 1.4% in weaning rate, but with reduction of 0.004 kg in weaning weight and 0.665 kg in cow weight due to negative genetic association between these traits. The proposed index and the relative importance identified for the economic traits can guide the selection decisions of smallholders, both in the choice of their animals and in the acquisition of bulls, cumulatively increasing the productivity of their herds.

Avaliaram-se modelos estatísticos com diferentes pressuposições para definir o que melhor descreva a presença de interação genótipo × ambiente no ganho de peso pós-desmama ajustado (GPD345) de bovinos Hereford, mediante o estudo de normas de reação ao ambiente, obtidas por regressão aleatória, usando uma abordagem bayesiana. Quatro modelos hierárquicos de normas de reação (MHNR) foram empregados por meio do programa INTERGEN. O MHNR K utiliza as soluções de grupos contemporâneos estimadas previamente pelo modelo animal padrão (MA) e as considera como nível ambiental para predizer as normas de reação e o MHNR S, que estima simultaneamente esses dois conjuntos de incógnitas. Para ambos os modelos, foram consideradas duas versões, uma com variância residual homogênea (hm) e outra heterogênea (ht). Pelo critério de informação da deviance e fator de Bayes, o MHRN Shm apresentou melhor ajuste aos dados e, pela deviance baseada na ordenada preditiva condicional, o melhor ajuste foi do MHNR Kht, enquanto, pelos três critérios, o pior ajuste foi obtido pelo modelo animal padrão. As herdabilidades estimadas nos MHNR foram crescentes nos gradientes ambientais em GPD345 de -60; 0 e +60 kg. As correlações genéticas estimadas entre o nível e inclinação das normas de reação foram de alta magnitude, entre 0,97 e 0,99, caracterizando efeito de escala em interação genótipo × ambiente. Os modelos hierárquicos de normas de reação são eficientes para descrever as alterações nos componentes de variância decorrentes do ambiente e para descrever a presença de interação genótipo × ambiente na característica GPD345 em bovinos Hereford.

It was evaluated statistical models with different assumptions to define the one that best describes the presence of genotype × environment interaction on adjusted post-weaning weight gain (PWG345) of Hereford cattle, through the study of reactions norms to the environment, obtained by random regression using a Bayesian approach. Four reaction norms hierarchical models (RNHM) were used through the INTERGEN program. The RNHM K uses the solutions of contemporary groups previously estimated by the standard animal model (AM) and considers them as environmental level for predicting the reaction norms and the RNHM S, which jointly estimate these two sets of unknowns. For both models, two versions were considered, one with a homogeneous (hm) and another with a heterogeneous (ht) residual variance. Based on the deviance information criterion and Bayes factor, RNHMs hm showed the best fit to the data, and by the deviance based on conditional predictive ordinate, the best fit was the RNHM Kht, whereas, by all the three criteria used, the worst fit was obtained by using the standard animal model. Heritabilities estimated on RNHM were increasing in the environmental gradients for PWG345, at -60 kg, 0 and +60 kg. The genetic correlation estimated between the level and slope of reaction norms was high, from 0.97 to 0.99, characterizing a scale effect on genotype × environment interaction. The reaction norms hierarchical models are efficient to describe the changes in variance components due to the environment and to describe the presence of genotype × environment interaction on PWG345 trait of Hereford cattle.

Os objetivos neste estudo foram utilizar um modelo animal multirracial para verificar a presença de heterogeneidade de variância genética entre as raças Angus e Nelore, avaliar a importância da variância devida à segregação entre essas duas raças e estimar os efeitos genéticos aditivos de raça, dominância e epistasia aditiva × aditiva. Foram utilizados neste estudo 4.016 registros de ganho de peso pós-desmame do rebanho de formação da raça Brangus-Ibagé da Embrapa Pecuária Sul, analisados por três modelos distintos: modelo animal multirracial com segregação, modelo animal multirracial sem segregação; e modelo animal tradicional. A heterose reduziu substancialmente em cruzamentos avançados. A variância genética média a posteriori da raça Angus (189 ± 26 kg²) foi maior que o dobro da obtida para a raça Nelore (82 ± 23 kg²) e a variância da segregação entre essas raças foi de 11 ± 5 kg². A alteração das estimativas das variâncias genéticas raciais foi insignificante quando a variância da segregação foi fixada em zero. Critérios bayesianos de escolha apontam o modelo multirracial sem segregação entre raças como uma alternativa parcimoniosa adequada para avaliação genética dessa população.

The objectives of this study were to use a multibreed animal model to verify the presence of heterogeneity of genetic variance between Angus and Nelore breeds, to verify the importance of the variance due to the segregation between these two breeds and to estimate breed additive genetic effects on the dominance and additive × additive epistatic effects. It was used in this study 4,016 records of post weaning weight gain from Brangus breed foundation herd from Embrapa Pecuária Sul, analyzed by three different models: multibreed animal model with segregation, multibreed animal model without segregation and traditional animal model. Heterosis was substantially reduced in advanced crosses. The posterior mean genetic variance of the Angus breed (189 ± 26 kg²) was more than twofold of that obtained for the Nelore breed (82 ± 23 kg²) and segregation variance between these two breeds was 11 ± 5 kg². The change in the breed genetic variance estimates was not significant when the segregation variance was set to zero. Bayesian choice criteria point to the multibreed animal model without segregation between breeds as an adequate parsimonious alternative for genetic evaluation of this population.

Objetivou-se avaliar diferenças nas estimativas dos valores genéticos dos reprodutores obtidos por meio de um modelo animal (MA) e de um modelo hierárquico normas de reação (MHNR) que considera o efeito da interação genótipo-ambiente (G*A). Foram utilizados dados do PROMEBO - Programa de Melhoramento de Bovinos de Carne, conduzido pela Associação Nacional de Criadores - "Herd Book Collares" dos rebanhos da raça Devon que participaram do programa entre 1980 e 2005, num total de 25.000 registros, com 14.973 animais conectados. Foi avaliada a característica de ganho pós-desmama padronizada para 345 dias (GPD345) por meio do programa INTERGEN. As normas de reação dos 25 reprodutores com maior número de filhos avaliados apresentam alteração de ordenamento e efeito escalar no gradiente ambiental. Correlações de ordem de Spearman entre os valores genéticos obtidos pelo MA e pelo MHNR nos níveis ambientais baixo, médio e alto foram utilizadas para comparar decisões de seleção baseadas nos diferentes modelos. Essas correlações variaram entre 0,12 e 0,99 e apontam alteração considerável no ordenamento, especialmente entre aqueles valores genéticos obtidos pelo MHNR em ambientes menos favoráveis que os obtidos pelo mesmo MHNR nos ambientes médios e superiores e aos obtidos pelo MA, quando considerados os 5% melhores touros. Os resultados indicam que, no processo seletivo, deve-se considerar a interação G*A para aumentar o ganho genético dessa população em cada ambiente específico.

The objective of this study was to evaluate differences in sire genetic values obtained by a conventional animal model (AM) and by a reaction norms hierarchical model (RNHM) that considers the genotype by environment interaction. A total of 25,500 records was used collected by PROMEBO - beef cattle improvement program of the National Breeders Association "Herd Book Collares" on Devon cattle born from 1980 though 2005. Post weaning gain 345 adjusted (PWG345) was the evaluated trait and the INTERGEN program was employed for data analysis. Reaction norms of the 25 sires with larger offspring showed ranking exchanges and scale effect in the environmental gradient. Spearman rank correlations between genetic values obtained by AM and RNHM at low, medium and high environmental levels were used to assess selection decision based on the different models. These correlations ranged from 0.12 and 0.99, therefore showing substantial changes in ranking, particularly between those genetic values obtained by the RNHM at low level compared to the same RNHM at medium and high levels and to AM, when considering the top 5% bulls. The results indicated that the selection process should consider the genotype by environmental interaction to maximize genetic gain and production of this population in each specific environment.

Os objetivos com este estudo foram verificar a presença de interação genótipo-ambiente e comparar modelos para o ajuste do ganho pós-desmama padronizado para 345 dias de bovinos da raça Devon, via normas de reação obtidas por regressão aleatória. Foram utilizados 14.973 registros coletados pelo Programa de Melhoramento de Bovinos de Carne entre 1980 e 2005. Para análise dos dados, foi utilizado o programa INTERGEN. Primeiramente, foi rodado o modelo animal convencional (MA), para comparação e estimativas do gradiente ambiental, com base nos desvios dos grupos de contemporâneos, e, em seguida, rodados os modelos hierárquicos de normas de reação com variâncias residuais homogêneas (MHNR) e heterogêneas (MHNRH). Nesses dois últimos, foram incluídos efeitos fixos de idade da vaca e idade do bezerro ao sobreano e efeitos aleatórios de grupos de contemporâneos e genéticos (nível e inclinação da norma de reação). No MHNR, as estimativas da variância residual, genética aditiva do nível e da inclinação da norma de reação e sua correlação genética foram, respectivamente, 272,02 ± 8,51; 340,38 ± 17,11; 0,119 ± 0,006 e 0,83 ± 0,01 e, no MHNRH, foram 401,96 ± 11,91; 177,86 ± 16,60; 0,076 ± 0,006 e 0,72 ± 0,02, respectivamente. A herdabilidade, bem como a variância genética, foi crescente no gradiente ambiental, caracterizando a existência de interação genótipo-ambiente. Com base nos Critérios de Informação Deviance, nos Fatores de Bayes e Pseudo Fatores de Bayes, o MHNR proporcionou melhor ajuste aos dados, sendo o mais apropriado para considerar a interação genótipo-ambiente dessa população.

The objectives of this study were to verify the presence of the genotype by environment interaction and to compare different models to fit Devon cattle post weaning gain standardized to 345 days, via reaction norms obtained by random regression. Data from 14,973 calves collected by the beef cattle improvement program from 1980 to 2005 were used. The INTERGEN program was used for data analysis. First, a standard animal model (AM) was fitted to serve as comparison basis and to provide estimates of the environmental gradient, based on contemporary group (CG) deviations and, next, the reaction norms hierarchical models with homogeneous (RNHM) and heterogeneous (RNHMH) residual variances were run. In these last two models, fixed effects of age of dam and age of calf at yearling and random contemporary group and genetic effects (level and slope of animal's reaction norms) were included. For the RNHM estimates of residual variance, reaction norm level and slope additive genetic variances and their genetic correlation were, respectively, 272.02 ± 8.51; 340.38 ± 17.11; 0.119 ± 0.006 and 0.83 ± 0.01, while for the RNHHM were 401.96 ± 11.91; 177.86 ± 16.60; 0.076 ± 0.006 and 0.72 ± 0.02, respectively. The heritability asa well as the genetic variance increased on the environmental gradient, characterizing that there is genotype by environment interaction. Based on the Deviance Information Criterion, Bayes Factors and Pseudo Bayes Factors, the NRHM provided superior fit to the data, being the most appropriate model to consider the genotype by environmental interaction of this population.

Dados extremos influenciados por fatores não considerados no modelo estatístico, podem enviesar as estimativas dos parâmetros e valores genéticos. Além disso, diversas características de importância econômica não seguem uma distribuição normal ou apresentam dados censurados. O objetivo deste trabalho é descrever e ilustrar a aplicação de modelos hierárquicos bayesianos para a detecção e mitigação de dados extremos e para análise de dados censurados. Primeiro, é apresentada a especificação tradicional do modelo animal em estágios hierárquicos sob o enfoque bayesiano, para dados não censurados com distribuição Normal. A seguir, esse modelo é generalizado pela introdução de uma variável de ponderação independente, que permite a especificação de densidades residuais de caudas longas da família de distribuições Normal/independente. Finalmente, para contemplar a análise de dados censurados, o modelo básico é ampliado pela inclusão de uma variável com distribuição normal truncada no limite inferior do valor observado da característica no momento da avaliação, para aqueles animais que ainda não completaram sua vida reprodutiva no momento da avaliação.

Data strongly influenced by factors not accounted for by the statistical model can bias estimates of genetic parameters and values. Moreover, several traits of economic importance do not follow a normal distribution or have censored data. The objective of this study is to describe and illustrate the application of hierarchical Bayesian models for the detection and muting of outliers and for the analysis of censored data. First, the traditional specification of the animal model in hierarchical stages is presented under the Bayesian approach for normally distributed uncensored data. Then, this model is extended by introducing an independent weighting variable, which allows for the specification of thick tail residual densities from the Normal/independent distribution family. Finally, to cover censored data analysis, the basic model is extended by the inclusion of a variable with truncated normal distribution based on the lower limit in the observed value of the trait at the evaluation time, for those animals that have not yet completed their reproductive life at the evaluation time.

O objetivo neste estudo foi avaliar o efeito dos fatores ambientais, do grupo de contemporâneos (GC), da data juliana do nascimento (DJN), da idade da vaca ao parto (IV) e da idade do bezerro à desmama (IT) sobre características de desempenho produtivo na fase pré-desmama de bovinos Devon criados no Rio Grande do Sul. Foram analisados o peso ao nascer (PN) e à desmama (PD) e o ganho do nascimento à desmama ajustado para 205 dias (GNDA). Foram utilizados registros de 23.369 animais, coletados pelo PROMEBO - Programa de Melhoramento de Bovinos de Carne, conduzido pela Associação Nacional de Criadores - "Herd Book Collares", nascidos entre 1980 e 2000. Destes animais, 16.593 tinham registro de PN, 22.530 tinham de PD e 22.259 de GNDA. As análises foram realizadas pelo PROC MIXED do SAS, cujo modelo considerou, além dos efeitos ambientais citados, o efeito aleatório do touro e o erro residual. A DJN foi considerada pela freqüência de nascimento dentro de classes de dez dias, em um total de 13 classes. A primeira, iniciando aos 190 dias do ano até a classe 13, dos 310 aos 320 dias. Para PN, os animais nascidos na classe 12 (out-nov) foram 3,15% mais pesados que os da classe 190 (jul), ao contrário do PD e GNDA, em que os melhores resultados foram na classe 190, respectivamente, 11,51 e 9,99% superiores aos nascidos na classe 13 (nov). O efeito da idade da vaca apresentou ponto de máxima em torno dos oito anos de idade, demonstrando tendência quadrática. O efeito da idade do bezerro apresentou tendência quadrática para GNDA e linear para PD. Esses resultados indicam que a inclusão dos efeitos ambientais no modelo de análise das características produtivas pré-desmama é necessária para que as avaliações genéticas sejam adequadamente ajustadas e, portanto, mais precisas e confiáveis.

The objective of this study was to evaluate the environmental effects of contemporary groups (CG), Julian birth date (JBD), age of dam at calving (AD) and age of calf at weaning (AC) on pre-weaning performance traits: birth weight (BW), weaning weight (WW) and 205 days adjusted weaning gain (WG) of Devon cattle raised in Rio Grande do Sul. A total of 23,369 records on animals, born from 1980 to 2000, collected by PROMEBO - beef cattle improvement program of Associação Nacional de Criadores Herd Book Collares were used. Analyses were performed by PROC MIXED of SAS, using a model that included CG, JBD and AD as fixed effects and sire and residual error as random effects. Average BW of animals that were born in Oct-Nov was 3.15% higher than BW of animals that were born in Jul, which were respectively for WW and WG 11.51% and 9.99% heavier than animals that were born in Nov. Age of dam showed a quadratic effect with maximal response on all traits around eight years,. The age of calf effect was quadratic on WG and linear on WW. These results indicate environmental effects should be included in models used for genetic evaluations of pre-weaning performance traits in order to improve their precision and reliability.