Produtividade acumulada (PAC) das matrizes em rebanhos Nelore do norte e nordeste do Brasil

Abstract

RESUMO -A produtividade acumulada (PAC) é um índice que indica precocidade sexual, periodicidade reprodutiva e potencial de produção de quilogramas de bezerros de matrizes bovinas. Foram analisadas 2.816 observações de fêmeas Nelore criadas em diferentes rebanhos do norte e nordeste do Brasil, recém incorporados ao Programa de Melhoramento Genético da Raça Nelore (PMGRN), com o objetivo de estimar os componentes de variância genética e residual e a herdabilidade da PAC. A média e o desvio-padrão observados para PAC foram 96,74 ± 46,70 kg de bezerros desmamados por vaca ao ano, com coeficiente de variação de 48,27%, inferior à média obtida para o conjunto de rebanhos integrantes do PMGRN. Fêmeas da raça Nelore Padrão obtiveram melhor resultado para PAC que às fêmeas Mocha. A herdabilidade estimada foi igual a 0,11 ± 0,06, sugerindo a existência de variabilidade genética suficiente para a inclusão desta característica em programas de melhoramento genético, ressaltando-se, no entanto, que seu progresso depende, sobretudo, de práticas de manejo mais eficientes.Palavras-chave: eficiência reprodutiva, fêmea zebu, herdabilidade, índice de seleção Accumulated Productivity of Nellore Cows Raised in North and Northeast of BrazilABSTRACT -The accumulated productivity (ACP) is an index that takes into account the total weight of calves weaned per cow (in kg), total time required for producing the calves and age at first calving. A study was conducted to estimate the components of genetic and residual variance and estimate the heritability of ACP index. Data set consisted of 2,816 observations of Nelore cows raised in different farms of the Brazilian North and Northeast. These farms participate in the Genetic Improvement Program of the Nelore Breed. The observed mean and respective standard deviation for ACP was 96.74 ± 46.70 kg of weaned calves/cow/year, with a coefficient of variation of 48.27%. This mean ACP, however, is lower than values estimated in other herds of the Nelore genetic program. Also, Standard Nelore cows showed higher ACP in comparison to cows of the Nelore Polled variety. Estimated heritability for ACP was 0.11 ± 0.06, suggesting that there is sufficient genetic variability that justify the use of ACP in genetic selection. However, results of such strategy depend, mainly, on efficient herd management.Key Words: heritability, reproductive efficiency, selection index, zebu IntroduçãoEm um mercado de grande competição como o atual, deve-se buscar a máxima produtividade para se otimizar a lucratividade. Neste contexto, em pecuária de corte, a produtividade do sistema está intimamente relacionada à eficiência reprodutiva das fêmeas que o compõem, visto que fêmeas mais precoces e férteis proporcionam aumento na taxa de nascimentos do rebanho, possibilitando maior produção de carne por ano.Nesse sentido, a eficiência reprodutiva destacase em programas de melhoramento como critério de seleção de fêmeas (Lôbo et al., 2004), adotando-se diferentes fórmulas para a avaliação desta eficiência em vacas de corte (Dinkel...

Genetic associations between accumulated productivity, and reproductive and growth traits in Nelore cattle

“…Our ACP heritability estimates for the Nelore breed are greater than those presented by Schwengber et al (2001) and Azevêdo et al (2005), i.e., 0.15 and 0.11± 0.06, respectively. Using a Bayesian inference, Faria et al (2007) found a 95% confidence interval for ACP heritability estimates of from 0.19 to 0.31.…”

“…Mean values and standard deviations, and minimum and maximum values for AFC, BW365, BW450, SC365, SC450, SC550 and SC730 are provided in Table 2. Schwengber et al (2001), Azevêdo et al (2005) and Faria et al (2007) noted smaller mean ACP in the Nelore breed (130.0 ± 35.0, 96.7 ± 46.7 and 134 kg weaning calves/dam/year, respectively) compared to those found here. Since these authors used data from herds in different regions of Brazil, the smaller means may result from the different genetic and environmental factors in each area.…”

Estimates of genetic parameters and genetic trends for reproductive traits and weaning weight in Tabapuã cattle1,2

“…The mean for CI1 was similar to that obtained by Pereira et al (2005) for Tabapuã cattle and lower than the means obtained for the Nelore and Guzerá breeds (Paneto et al, 2008;Panetto et al, 2010;Yokoo et al, 2012). The mean for ACP was similar to that obtained by Rosa (1999), lower than that observed by Grossi et al (2008), and higher than the values obtained by Schwengber et al (2001) and Azevêdo et al (2005) of 130 ± 35 and 96.74 ± 46.7 kg of calves per dam per year, respectively, for Nelore cattle.…”

Phenotypic relationship of female sexual precocity with production and reproduction traits in beef cattle using multivariate statistical techniques

“…Cumulative productivity was not associated with any of the factors considered. The lack of association of this trait with a specific latent variable in factor analysis could be due to the fact that this trait comprises variables such as pregnancy rate, reproductive periodicity and dams productive ability (kg of calves produced during their life) (Lôbo et al 2000;Azevêdo et al 2005). However, principal component analysis revealed a favourable association between the anticipation of reproductive life and cumulative productivity Figure 2.…”