E.C. Mattos

Genetic relationship between growth and reproductive traits in Nellore cattle

The objective of this study was to evaluate the genetic relationship between postweaning weight gain (PWG), heifer pregnancy (HP), scrotal circumference (SC) at 18 months of age, stayability at 6 years of age (STAY) and finishing visual score at 18 months of age (PREC), and to determine the potential of these traits as selection criteria for the genetic improvement of growth and reproduction in Nellore cattle. The HP was defined as the observation that a heifer conceived and remained pregnant, which was assessed by rectal palpation at 60 days. The STAY was defined as whether or not a cow calved every year up to the age of 6 years, given that she was provided the opportunity to breed. The Bayesian linear-threshold analysis via the Gibbs sampler was used to estimate the variance and covariance components applying a multitrait model. Posterior mean estimates of direct heritability were 0.15 ± 0.00, 0.42 ± 0.02, 0.49 ± 0.01, 0.11 ± 0.01 and 0.19 ± 0.00 for PWG, HP, SC, STAY and PREC, respectively. The genetic correlations between traits ranged from 0.17 to 0.62. The traits studied generally have potential for use as selection criteria in genetic breeding programs. The genetic correlations between all traits show that selection for one of these traits does not imply the loss of the others.

Comparison of different models to estimate genetic parameters for carcass traits in a commercial broiler line

The effect of genetic and non-genetic factors for carcass, breast meat and leg weights, and yields of a commercial broiler line were investigated using the restricted maximum likelihood method, considering four different animal models, including or excluding maternal genetic effect with covariance between direct and maternal genetic effects, and maternal permanent environmental effect. The likelihood ratio test was used to determine the most adequate model for each trait. For carcass, breast, and leg weight, and for carcass and breast yield, maternal genetic and permanent environmental effects as well as the covariance between direct and maternal genetic effects were significant. The estimates of direct and maternal heritability were 0.17 and 0.04 for carcass weight, 0.26 and 0.06 for breast weight, 0.22 and 0.02 for leg weight, 0.32 and 0.02 for carcass yield, and 0.52 and 0.04 for breast yield, respectively. For leg yield, maternal permanent environmental effect was important, in addition to direct genetic effects. For that trait, direct heritability and maternal permanent environmental variance as a proportion of the phenotypic variance were 0.43 and 0.02, respectively. The results indicate that ignoring maternal effects in the models, even though they were of small magnitude (0.02 to 0.06), tended to overestimate direct genetic variance and heritability for all traits.

Estimates of heritability and genetic correlations for meat quality traits in broilers

Broiler meat quality is one of the primary factors considered by the poultry industry. This study was conducted to estimate heritability and genetic correlation coefficients for meat quality traits in a single male broiler line. The meat ultimate pH (24 h after slaughter) and lightness presented the highest heritability estimates. Given the estimated genetic correlations, the pH measured at 15 min and 24 h after slaughtering, as well as lightness, were characterized by a close and negative genetic relationship with water holding capacity traits. In contrast, meat quality traits exhibited only non-significant genetic correlations with performance and carcass traits. Noticed exceptions were breast weight, which was genetically and favorably associated with the initial pH and thawing-cooking losses, and ultrasound record of pectoral muscle depth, which was genetically and unfavourably associated with the shear force of meat. Meat pH values at 24 h after slaughtering or lightness may be a favorable selection criterion for the poultry industry for improving meat quality, since these traits are associated with the water holding capacity of the meat. Out of the traits studied, lightness is most easily assessed on the industrial slaughtering line. The direct selection for breast weight could improve the initial pH and thawing-cooking losses of meat, even as selection for ultrasound records of Pectoralis major may affect the meat tenderness in this line

Influência da interação genótipo x ambiente sobre o peso à desmama em bovinos da raça Nelore

The effects of genotype x environment interaction on weaning weight in Nellore cattle were evaluated. A total of 45,697 records of weaning weight adjusted for 205 days obtained from three farms were analyzed. The farms were organized in pairs and analyzed by single-trait analysis, as if they were only one herd. Afterwards, the pairs were submitted to multiple-trait analyses, once the same trait was considered as a distinct trait in each farm. The variance components were estimated by Restricted Maximum Likelihood, using the program MTDFREML. The genetic correlation coefficients varied from 0.79 to 1.00. The Expected Progeny Differences (EPD) were estimated using de same computational program. Later, the sires were organized in accordance with their EPD, selecting the 30% best classified sires. Pearsons correlations were estimated among the EPD of animals selected in two different environments, in order to verify changes in their classification. The Pearsons correlations extended from 0.96 to 0.99, suggesting small or inexistent effect of genotype x environment interaction in the herds included in this study.

Métodos de estimação de efeitos genéticos não-aditivos para características de peso e perímetro escrotal em bovinos de corte mestiços

The objective of this study was to investigate, in a population of crossbred cattle, the obtainment of the non-additive genetic effects for the characteristics weight at 205 and 390 days and scrotal circumference, and to evaluate the consideration of these effects in the prediction of breeding values of sires using different estimation methodologies. In method 1, the data were pre-adjusted for the non-additive effects obtained by least squares means method in a model that considered the direct additive, maternal and non-additive fixed genetic effects, the direct and total maternal heterozygosities, and epistasis. In method 2, the non-additive effects were considered covariates in genetic model. Genetic values for adjusted and non-adjusted data were predicted considering additive direct and maternal effects, and for weight at 205 days, also the permanent environmental effect, as random effects in the model. The breeding values of the categories of sires considered for the weight characteristic at 205 days were organized in files, in order to verify alterations in the magnitude of the predictions and ranking of animals in the two methods of correction data for the non-additives effects. The non-additive effects were not similar in magnitude and direction in the two estimation methods used, nor for the characteristics evaluated. Pearson and Spearman correlations between breeding values were higher than 0.94, and the use of different methods does not imply changes in the selection of animals.

Phenotypic correlations among meat quality traits in broilers

The goals of this research were to estimate the phenotypic correlations among various meat quality traits from a male broiler line and to describe the relation among these variables. Phenotypical correlations were determined among quality traits, isolating the effects of slaughter date, the age of the mother and sex. The evaluated traits were pH measurements taken at time 0 and at 6 and 24 hours after slaughtering, color parameters, water loss due to exudation, thawing and cooking of the meat, and shear force. Important associations (P 0.05) to the other traits of the meat, whereas the pH at 24 hours after slaughter was able of directly interfering with the attributes of the meat, since this trait was inversely related with lightness and water losses, which indicates an effect of pH fall along 24h after slaughtering on protein denaturation. This study demonstrates that the variables of poultry meat quality are related and that there is a phenotypical association between lightness and cooking losses and the other attributes of the meat. The pH at 24 hours after slaughtering, lightness and cooking losses could be efficient meat quality indicators in this broiler line.

Estimativas de adaptabilidade e estabilidade fenotípicas em características produtivas em bovinos de corte mestiços criados em diferentes ambientes

Data from 39,212 weaning weights and 16,546 yearling weights and weight gain from weaning to 160 days after weaning, were used to evaluate a methodology to discriminate estimates of phenotypic adaptability and stability. Nine genotypic compositions distributed in six environments for weaning weight, and in five environments for yearling weight and weight gain from weaning to 160 days post weaning, were analyzed. The averages, standard deviations and coefficients of variation for weaning weight, yearling weight and weight gain from weaning to 160 days post weaning were: 204.3± 22.6kg and 11.1%; 280.4± 25.9kg and 9.2%; and l64.8± 18.1kg and 28%, respectively. The genotype by environment interaction suggests that the best genotype combinations can not be recommended for all the environments. The adaptability analysis was efficient to discriminate genotype combination within environment.

Definição de grupos genéticos aditivos visando melhor predição de valores genéticos em bovinos de corte

The paper aims to analyze the structure of additive genetic groups as an alternative to include animals with unknown parentage in genetic evaluation. Several traits were studied: weaning weight; yearling weight; post-weaning weight gain in 345 days; scrotal circumference at 18 months of age; and visual muscling scores at 18 months of age. As a control group it was used a database where all animals had known paternity. Thus, three scenarios were defined where 30%; 50% or 70% of the observations were randomly taken as animals with unknown parentage. For these three simulated databases, the strategies considered to define additive genetic groups were: effect of year at birth; effect of farm at birth; effect of year and farm at birth; and a negative control group, which considered animals with unknown paternity. The most appropriate strategy for additive genetic group was chosen as the one that resulted in a higher regression coefficient and additive genetic value closest to the predicted for those animals in the control group. The results considering the strategy of additive genetic show large agreement with the control group. Among the strategies proposed, farm of birth and year of birth of the animal with unknown parentage achieved the best results.

Inclusão da epistasia em modelo de avaliação genética de bovinos de corte compostos

Composite bovine data was analyzed with the objective of evaluating the effect of the epistasis parameter in the models of genetic evaluation. The analyzed characteristics were weight at 205 (W205) and 390 days (P390), and scrotal circumference at 390 days (SC390). The analysis were done by the maximum likelihood method, considering two models: model 1, which included as covariates the direct and maternal additive effects, and non-additive of the heterozygosis for the direct and total maternal, and model 2, which also considered the direct epistasis direct. The Akaike Information Criteria (AIC) and the Bayesiano of Schwartz Information Criteria (BIC) were used for the comparison of the models and the test of ratio of likelihood. The inclusion of the epistasis effects on the model of the genetic evaluation did not alter much the estimation of the genetic additive (co)variances components and, consequently the heritability. However, it was significantly superior by the likelihood ratio test for the studied characteristics. Through the BIC, model 2 was more adequate only for W205. For the genetic analysis of that population the model that considers the epitasis is the more adequate.

Inclusion of cytoplasmic lineage effect and direct-maternal genetic covariance for genetic evaluation of growth traits in Nellore cattle.

We evaluated the impact of cytoplasmic lineage effects (Lc) for growth traits on genetic evaluation, including the genetic covariance between direct and maternal effects (σam). Pedigree data from 496,190 Nellore animals and observations on birth weight (BW, N = 243,391), weaning weight (WW, N = 431,681), and post-weaning weight gain adjusted to 345 days (PWG, N = 172,131) were analyzed. Four univariate models were used to obtain estimates of (co)variance components using the restricted maximum likelihood method in the BLUPF90 program. Model 1 included Lc and σam. Model 2 included Lc and σam was set to zero. Model 3 did not include Lc. Model 4 did not include Lc and σam was set to zero. These models considered the effects of the Lc as random. Phenotypic variance obtained through cytoplasmic lineage effects was determined for all traits, ranging from 0.07 to 0.15, 0.15 to 0.03, and 0.05 to 0.03% for BW, WW, and PWG, respectively, for models 1 and 2. Correlations between direct and maternal genetic components were positive for WW and negative for BW and PWG. No differences were observed for genetic parameter estimates or animal ranking with the inclusion of σam. For BW, the likelihood ratio suggested that model 1 best fits the data, while model 4 was the most appropriate for WW and PWG. Thus, these models are recommended for genetic evaluations. Despite the low magnitude of cytoplasmic lineages, this effect could predict breeding value and improve the selection of animals for BW in this Nellore population.