Tendência genética para peso adulto, escores visuais e características de crescimento em bovinos de corte da raça Nelore

Mature weight (MW) of cows is related to the costs of their production. Usually, cows with moderate MW are more efficient in challenging environments, such as those available in the production systems in Brazil. In the present study, the selection index comprises the following traits: conformation, finishing precocity, musculature at weaning (WC, WP, WM) yearling (YC, YP and YM), scrotal circumference at yearling (SC), days to gain 160kg from birth to weaning (D160) and 240kg after weaning (D240). This are related to birth weight gain at weaning (WG) and from weaning to yearling (YG). The mature (MW) and birth weight (BW) traits were not considered in the selection index. The aim of this study was to estimate the values for the genetic trends (GT) of some important selection (MW) and economic traits (BW). A bi-character analysis of MW and other characteristics was performed to estimate the (co)variance components and genetic parameters. The GT results obtained for MW were null (0.0065% or 0.02718kg per year) in the period 1990-2007. The GT values were determined for BW (-0.0650% or -0.02017kg), WG (0.0758% or 0.0865kg), YG (0.1051% or 0.11377kg), and MW (0.0393% or 0.11276kg) per year. The visual score values (in score units) were also determined for GTat weaning [WC (0.2310%; 0.00707), WP (0.3624%; 0.3623%),aWM (0.01149; 0.01087)] yearling [YC (0.3256%; 0.00990), YP (0.4795%; 0.01496),YM (0.5041%; 0.01457)] per year. Index-based selection was effective to promote genetic progress in WG, WC, WP, WM, YG, YC, YP, and YM characteristics keeping BW and MW constant.O peso adulto das vacas (PV) está relacionado com os custos de produção. Em geral, vacas com PV moderados são mais eficientes em ambientes desafiadores, como aqueles disponíveis nos sistemas de produção no Brasil. No presente estudo, o índice de seleção compreende as seguintes características: conformação, precocidade e musculatura nas fases da desmama (CD, PD e MD) e sobreano (CS, PS e MS), circunferência escrotal no sobreano (CE), dias para ganhar 160kg do nascimento até a desmama (D160) e 240kg pós-desmama (D240), que estão relacionadas com os ganhos de peso do nascimento à desmama (GD) e, da desmama ao sobreano (GS). As características PV e PN não foram consideradas no índice de seleção. O objetivo deste estudo foi estimar os valores das tendências genéticas (TG) das importantes características de seleção (PV) e econômicas (PN). Para estimar os componentes de (co)variâncias e os dados genéticos, foram realizadas análises bi-caracter de PV com as demais características. Os resultados de TG obtidos para PV foram nulos (0,0065% ou 0,02718kg por ano) no período de 1990 á 2007. Os valores de TG foram estimados para PN (-0,0650% ou -0,02017kg), GD (0,0758% ou 0,0865kg), GS (0,1051% ou 0,11377kg) e PF (0,0393% ou 0,11276kg) por ano. Os valores dos escores visuais (em unidades de escore) foram determinados para TG à desmama [CD (0,2310%; 0,00707), PD (0,3624%; 0,3623%) e MD (0,01149; 0,01087)] e sobreano [CS (0,3256%; 0,00990), PS (0,4795%; 0,01496) e MS (0,5041%; 0,01457)] ao ano. A seleção baseada no índice foi efetiva para promover o progresso genético nas características de GD, CD, PD, MD, GS, CS, PS e mantendo PN e PV constantes

Direct and maternal annual genetic changes for selected traits at weaning and yearling in beef cattle

Heritability and direct and maternal genetic changes were estimated in Nellore cattle for the following traits: birth to weaning weight gain (BWG), weaning to yearling weight gain (YWG), weaning conformation (WC), weaning precocity (WP), weaning muscling (WM), yearling conformation (YC), yearling precocity (YP), yearling muscling (YM) and yearling scrotal circumference (SC). Direct and maternal heritability for weaning traits were 0.21±0.03 and 0.13±0.01 (BWG); 0.19±0.03 and 0.07±0.01 (WC); 0.22±0.03 and 0.07±0.01 (WP); 0.20±0.03 and 0.07±0.01 (WM), respectively. For yearling traits, direct heritability were 0.19±0.04 (YWG); 0.32±0.05 (YC); 0.37±0.05 (YP); 0.38±0.05 (YM) and 0.41±0.04 (SC). Positive and significant direct genetic changes (p 0.05) maternal genetic trends, with values of -0.084 kg year-1 (BWG), -0.004 units year-1 (WC), -0.004 units year-1 (WP) and -0.004 units year-1 (WM). Thus, greater emphasis should be given for maternal genetic merit of weaning traits in this population, if improvements in maternal ability were desirable

Formando lotes uniformes de reprodutores múltiplos e usando-os em acasalamentos dirigidos, em populações Nelore

Um programa com base em análise de conglomerados foi desenvolvido com o objetivo de formar lotes de touros geneticamente semelhantes para serem empregados como grupos de reprodutores múltiplos em acasalamentos dirigidos. Para o cálculo das distâncias entre os animais, as diferenças esperadas na progênie (DEPs) de nove características pré e pós-desmama foram padronizadas pelos respectivos desvios-padrão e ponderadas pelos mesmos fatores usados na construção do índice de seleção. O critério de formação dos lotes foi o de minimizar o somatório de todas as distâncias entre todos os possíveis pares de touros. O programa foi testado com 158 touros destaques de um rebanho Nelore. Um conjunto de 4740 vacas do mesmo rebanho foi utilizado para avaliar três situações de acasalamentos, quanto à produção de animais geneticamente superiores: (1) ao acaso; (2) dirigido, por meio do programa de acasalamentos dirigidos (PAD), com monta controlada; e (3) dirigido, por meio do PAD, com grupos de reprodutores múltiplos. Por meio de análise de componentes principais, foram avaliados os biotipos genéticos existentes nestas categorias de animais. Os valores extremos das médias das DEPs dos lotes e as do conjunto de touros foram muito semelhantes, indicando a capacidade do programa de preservar a maior parte da variância total. O uso do PAD, em relação à opção de acasalamentos ao acaso, fez com que as variâncias das DEPs dos produtos fossem triplicadas e, assim, permitiu incremento de 70% no número de animais a receberem o Certificado Especial de Identificação e Produção (CEIP) quando estipulou-se, como valor mínimo para a emissão deste, o menor índice dos 20% melhores produtos dos acasalamentos ao acasos. O primeiro componente principal das vacas indicou que dias para ganhar 240 kg pós-desmama e perímetro escrotal ajustado para idade e peso foram as características menos relevantes para explicar a variabilidade total no pré e no pós-desmama; o segundo discriminou entre animais melhores em desenvolvimento e nas avaliações visuais à desmama e o contrário ao sobreano, e animais com características opostas a estas; o terceiro componente ressaltou diferenças em precocidade reprodutiva. Para os touros e grupos de reprodutores, mesmo após intensa seleção, a maior parte da variação ainda existente esteve associada a diferenças em precocidade.Cluster analysis principles were used to allot bulls to be used as Multiple Service sires (MS). Expected Progeny Differences (EPDs) on pre- and postweaning traits were used to calculate distances between bulls. EPDs were standardized and weighed to form a final selection index. The criteria to form lots was based on minimizing the sum of all standardized distances for all possible pairs of bulls. The program was tested on a set of 158 top bulls from a Nelore herd. A set of 4,740 breeding cows was used to evaluate three breeding strategies with the goal of producing genetically superior individuals: (1) random mating; (2) single sire under designed matings by a specific program (PAD); and (3) lots of multiple sires under designed matings using PAD. Principal components was used to obtain the genetic biotypes existing in these populations. Extreme values in EPDs amongst MS lots averages and overall were very similar, indicating the program's ability to preserve total variance. Variances of EPDs from calf crops obtained under the use of PAD were increased three fold. Using designed matings by PAD allowed an increase of 70% in the number of animals which would be recognized with official and fiscal benefits in comparison with random mating. First principal components for cows, indicated that most genetic variability is accounted for preweaning traits and visual scores at postweaning; the second indicated animals can be contrasted as good weaners and poor performer at yearling and vice-versa; the third component showed diferences in sexual precocity. For single and multiple sires, despite the stronger selection pressure behind them, most of the remaining genetic variability is associated with differences in precocity (traits associated with early finishing).Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Genetic parameters of age at first calving, weight gain, and visual scores in Nelore heifers

ABSTRACT This study aimed at estimating the heritability of age at first calving and of performance traits included in the selection index and the genetic correlations between age at first calving and these performance traits. Data were extracted from the Conexão Delta G database and only data from herds in which heifers were bred younger than 24 months of age were used, resulting in a file with 331,310 evaluated animals. The following traits were included in the analyses: age at first calving, birth to weaning gain, post-weaning weight gain, visual scores of conformation, precocity, and muscling evaluated at weaning and in yearling heifers. Covariance components were obtained by bi-character analyses between traits. An alternative age at first calving was also taken into account, in which all heifers were used, including those that were mated and did not calve. Covariance components and estimates of the effects included in the model were obtained using the software program DMU. Heritability estimates were 0.11 and 0.13 for age at first calving and alternative age at first calving, 0.38 for birth to weaning gain, and 0.13 for post-weaning weight gain. Visual score estimates ranged between 0.16 and 0.18 at weaning and 0.19 and 0.29 in yearlings. Genetic correlation estimates of the traits were low, but in the desirable direction. Selection for birth to weaning gain and visual scores does not have a negative effect on age at first calving or alternative age at first calving

Genetic parameters of age at first calving, weight gain, and visual scores in Nelore heifers

This study aimed at estimating the heritability of age at first calving and of performance traits included in the selection index and the genetic correlations between age at first calving and these performance traits. Data were extracted from the Conexão Delta G database and only data from herds in which heifers were bred younger than 24 months of age were used, resulting in a file with 331,310 evaluated animals. The following traits were included in the analyses: age at first calving, birth to weaning gain, post-weaning weight gain, visual scores of conformation, precocity, and muscling evaluated at weaning and in yearling heifers. Covariance components were obtained by bi-character analyses between traits. An alternative age at first calving was also taken into account, in which all heifers were used, including those that were mated and did not calve. Covariance components and estimates of the effects included in the model were obtained using the software program DMU. Heritability estimates were 0.11 and 0.13 for age at first calving and alternative age at first calving, 0.38 for birth to weaning gain, and 0.13 for post-weaning weight gain. Visual score estimates ranged between 0.16 and 0.18 at weaning and 0.19 and 0.29 in yearlings. Genetic correlation estimates of the traits were low, but in the desirable direction. Selection for birth to weaning gain and visual scores does not have a negative effect on age at first calving or alternative age at first calving