A epigenética é definida como mudanças na expressão gênica que podem ser herdadas e que não alteram a sequência do DNA. Existem dois mecanismos epigenéticos principais, a metilação do DNA e a modificação de histonas. Também se destaca o imprinting genômico, o qual está relacionado com a regulação gênica quando apenas um alelo (herdado do pai ou da mãe) se expressa. A herança epigenética transgeracional consiste da herança de marcas epigenéticas através de células germinativas, que controla os padrões de expressão gênica e são passados de uma geração para a outra. Dentro do programa de melhoramento animal é importante avaliar a extensão com que a herança epigenética transgeracional também afeta a eficiência da seleção. Uma melhor compreensão dos mecanismos epigenéticos e seus efeitos transgeracionais no desempenho dos animais poderá permitir maiores ganhos sobre as características de importância econômica.

1. The aim of this study was to investigate the associations between several carcass, performance and meat quality traits in broilers through factor analysis and use the latent variables (i.e. factors) as pseudo-phenotypes in genetic evaluations. 2. Factors were extracted using the principal components method and varimax rotation algorithm. Genetic parameters were estimated via Bayesian inference under a multiple-trait animal model. 3. All factors taken together explained 71% of the original variance of the data. The first factor, denominated as ‘weight’, was associated with carcass and body weight traits; and the second factor, defined as ‘tenderness’, represented traits related to water-holding capacity and shear force. The third factor, ‘colour’, was associated with traits related to meat colour, whereas the fourth, referenced as ‘viscera’, was related to heart, liver and abdominal fat. 4. The four biological factors presented moderate to high heritability (ranging from 0.35 to 0.75), which may confer genetic gains in this population. 5. In conclusion, it seems possible to reduce the number of traits in the genetic evaluation of broilers using latent variables derived from factor analysis.

1. The aim of the following experiment was to estimate transgenerational epigenetic variance for egg quality traits using genealogical and phenotypic information in meat-type quail. Measured traits included egg length (EL) and width (EWD), albumen weight (AW), shell weight (SW), yolk weight (YW) and egg weight (EW). 2. A total of 391 birds were evaluated for egg quality by collecting a sample of one egg per bird, during three consecutive days, starting on the 14th d of production. Analyses were performed using mixed models including the random epigenetic effect. Variance components were estimated by the restricted maximum likelihood method. A grid-search for values for the auto-recursive parameter (λ) was used in the variance components estimation. This parameter is directly related to the reset (v) and epigenetic transmissibility (1 - v) coefficients. 3. The epigenetic effect was not significant for any of the egg quality traits evaluated. Direct heritability estimates for egg quality traits ranged in magnitude from 0.06 to 0.33, whereby the higher estimates were found for AW and SW. Epigenetic heritability estimates were low and close to zero (ranging from 0.00 to 0.07) for all evaluated traits. 4. The current breeding strategies accounting for additive genetic effect seem to be suitable for egg quality traits in meat-type quail.

The intense selection process for economic traits conducted by the poultry breeding programs has been caused several changes in broiler meat quality. A database belonging to a selection program of a broiler male line was used to estimate heritability and genetic correlations for feed conversion ratio and meat quality traits, which were: initial and final pH, lightness, drip loss, thawing loss and shear force. Two-trait analyses were performed and the components of co(variance) and genetic parameters were determined using the Bayesian approach and the GIBBS3F90 software. The heritability estimate found for feed conversion ratio (0.52) showed high influence of direct additive genetic effects on the expression of this trait; therefore, this trait is able to respond to selection. The genetic correlation estimates obtained (-0.50 to 0.33) were indicative of important associations between feed conversion ratio and meat quality traits. The selection to improve feed conversion ratio may cause injury in greater or lesser degree for L*, drip loss (DL), thawing loss (TL) and shear force (SF) in broilers. It is recommended the monitoring of consequences of feed conversion ratio used as selection criteria or meat quality traits in broilers, due to its unfavorable indirect selection for these variables in this population. Breeding methods for efficiency improvements in broilers feed are suggested, which also benefit sensorial and functional properties of the meat.