Estimação de parâmetros genéticos em tamanho de leitegada de suínos utilizando análises de características múltiplas

Abstract

RESUMO-Registros de animais da raça Large White foram utilizados para estimar componentes de co-variâncias e parâmetros genéticos para a característica número de leitões nascidos como medida do tamanho de leitegada. Na obtenção dos componentes de co-variâncias e dos parâmetros genéticos, utilizou-se o método da Máxima Verossimilhança Restrita, com o algoritmo Livre de Derivadas, por meio do programa MTDFREML. O modelo misto continha o efeito fixo de grupo contemporâneo e os efeitos aleatórios genético aditivo direto e residual. Dados das primeiras quatro parições foram usados em duas análises: análises unicaracterísticas e análise multicaracterística separada em séries de análises bicaracterísticas, na qual cada parição foi tratada como característica diferente. As estimativas de herdabilidades aditivas diretas para as parições obtidas nas análises multicaracterísticas foram consistentes com as estimativas obtidas nas análises unicaracterísticas, que variaram de 0,14 a 0,20. Estimativas de correlação fenotípica foram menores que as correlações genéticas. As correlações genéticas foram menores que 0,75 em todas as parições, exceto entre a terceira e a quarta parição, cuja correlação foi alta (0,91). A menor correlação genética foi observada entre a primeira e a segunda ordem de parto (0,60). Palavras-chave: características reprodutivas, correlação genética, herdabilidade, número de leitões nascidos, REML ABSTRACT-Data from the first four parities of Large White pigs were used to estimate (co)variance components and genetic parameters for litter size (LS) in single trait and multi-trait analyses. The (co)variance components and genetic parameters were estimated by restricted maximum likelihood using the MTDFREML program. LS in each parity was considered a different trait and the models included contemporary group as fixed effect and additive direct genetic and residual as random effects. Heritability estimates of LS in different parities in single trait analyses ranged from 0.14 to 0.20. Estimates of heritability in multi-trait analyses were similar to those obtained in single trait analyses. Phenotypic correlation estimates were lower than the genetic ones. Genetic correlations between parities were lower than 0.75, except for the estimate between the third and fourth parities, which was the highest one (0.91). The smallest genetic correlation (0.60) was observed between the first and second parities.

Avaliação genética do tamanho de leitegada em suínos das raças Landrace e Large White

“…2). Esse fato sugere a existência de diferentes bases genéticas atuando no tamanho da leitegada ao longo da vida reprodutiva das porcas (Barbosa et al, 2008).…”

Estimation of variance components, genetic parameters and genetic trends for litter size of swines

“…See et al (1993), studying three purebred breeds and using a model that only included first parity records, observed heritability estimates for number of pigs born alive of about 0.13. Ferraz & Johnson (1993) reported heritabilities of 0.14 for number of piglets born alive in Large White pigs using a model that only included additive effects and Barbosa et al (2008), using data from the first four parities of Large White sows, estimated heritabilities in single and multiple trait analyses ranged from 0.14 to 0.20. These results are similar to those found in the present study.…”

“…These variations are due to the number and quality of the records and the models and estimation methods used. Additionally, there are some controversies in the literature as to whether litter size in different parities should be considered as repeated measurements of the same trait (Southwood & Kennedy, 1990;See et al, 1993;Crump et al, 1997;Lourenço et al, 2008) or as different traits (Irgang et al, 1994;Roehe & Kennedy, 1995;Rydhmer et al, 1995;Barbosa et al, 2008).…”

Differential expression of genes in follicular cells of swines

“…An increase in reproductive efficiency has been observed over the last few decades, mainly as a result of genetic improvement of the herds. Among reproduction traits, reproductive performance, especially the number of piglets per litter, is fundamental for the success of pig production, where the increase in prolificity reduces production costs (Barbosa et al, 2008). However, this trait is sex-limited and shows low heritability of about 0.10 (Chen et al, 2003) and 0.22 (Torres-Filho et al, 2005), which represents a strong candidate for marker-assisted selection.…”

“…Concerning to litter size, two factors are intimately related, ovulation rate and embryo survival or mortality. The ovulation rate refers to the number of oocytes released during the estrus period and it is one of the most important components of prolificity (Caetano et al, 2003). Because of this, the study of gene expression in ovarian follicular cells during different phases of the estrus cycle may have a high impact on the understanding of the reproductive biology of the swine, leading to the improvement of ovulation rates and consequently to an increase in litter size.…”