Marcelo Corrêa da Silva

Genetic Analysis of Growth Traits in Polled Nellore Cattle Raised on Pasture in Tropical Region Using Bayesian Approaches

Components of (co)variance and genetic parameters were estimated for adjusted weights at ages 120 (W120), 240 (W240), 365 (W365) and 450 (W450) days of Polled Nellore cattle raised on pasture and born between 1987 and 2010. Analyses were performed using an animal model, considering fixed effects: herd-year-season of birth and calf sex as contemporary groups and the age of cow as a covariate. Gibbs Samplers were used to estimate (co)variance components, genetic parameters and additive genetic effects, which accounted for great proportion of total variation in these traits. High direct heritability estimates for the growth traits were revealed and presented mean 0.43, 0.61, 0.72 and 0.67 for W120, W240, W365 and W450, respectively. Maternal heritabilities were 0.07 and 0.08 for W120 and W240, respectively. Direct additive genetic correlations between the weight at 120, 240, 365 and 450 days old were strong and positive. These estimates ranged from 0.68 to 0.98. Direct-maternal genetic correlations were negative for W120 and W240. The estimates ranged from −0.31 to −0.54. Estimates of maternal heritability ranged from 0.056 to 0.092 for W120 and from 0.064 to 0.096 for W240. This study showed that genetic progress is possible for the growth traits we studied, which is a novel and favorable indicator for an upcoming and promising Polled Zebu breed in Tropical regions. Maternal effects influenced the performance of weight at 120 and 240 days old. These effects should be taken into account in genetic analyses of growth traits by fitting them as a genetic or a permanent environmental effect, or even both. In general, due to a medium-high estimate of environmental (co)variance components, management and feeding conditions for Polled Nellore raised at pasture in tropical regions of Brazil needs improvement and growth performance can be enhanced.

Spatialization of climate, physical and socioeconomic factors that affect the dairy goat production in Brazil and their impact on animal breeding decisions

Brazil has high climate, soil and environmental diversity, as well as distinct socioeconomic and political realities, what results in differences among the political administrative regions of the country. The objective of this study was to determine spatial distribution of the physical, climatic and socioeconomic aspects that best characterize the production of dairy goats in Brazil. Production indices of milk per goat, goat production, milk production, as well as temperature range, mean temperature, precipitation, normalized difference vegetation index, relative humidity, altitude, agricultural farms; farms with native pasture, farms with good quality pasture, farms with water resources, farms that receive technical guidance, family farming properties, non-familiar farms and the human development index were evaluated. The multivariate analyses were carried out to spatialize climatic, physical and socioeconomic variables and so differenciate the Brazilian States and Regions. The highest yields of milk and goat production were observed in the Northeast. The Southeast Region had the second highest production of milk, followed by the South, Midwest and North. Multivariate analysis revealed distinctions between clusters of political-administrative regions of Brazil. The climatic variables were most important to discriminate between regions of Brazil. Therefore, it is necessary to implement animal breeding programs to meet the needs of each region.

Tendência genética para características relacionadas à velocidade de crescimento em bovinos Nelore da região norte do Brasil

The objective was to estimate the (co) variance, genetic parameters and trends for the characteristics, days to gain 160 kg (D160) in the pre-weaning phase, and days to gain 240 kg (D240) in the post-weaning phase, in Nellore cattle, grown in Northern Brazil. Records analyzed were of animals raised on pasture in northern Brazil, provided by the Brazilian Association of Zebu Breeders - ABCZ, and collected from 1997 to 2007. Contemporary groups (herd, year, birth season and gender) were used as a fixed effects model, and age at calving as a covariant. Estimates of (co) variance were obtained using the MTDFREML software. The averages observed for D160 and D240 were 235 ± 46 days and 578 ± 171 days respectively. Estimates of heritability for D160, due to the additive genetic and maternal effect, were 0.27 ± 0.03 and 0.35 ± 0.04, respectively. For D240, the heritability for the additive genetic effect was 0.28 ± 0.03. This indicates that selection for any of the characteristics will result in genetic progress. Potential genetic gains due to the additive genetic effect, were 1.02 and 3.17 days per year for D160 and D240 respectively. This corresponds to 0.43 and 0.55% of the average of days to gain 160 kg (pre-weaning) and 240 kg (post-weaning) respectively. Although weight is currently used as the selection criteria, the genetic trends for D160 and D240 indicated the existence of genetic progress when using these characteristics as the selection criteria.

Selection Indices and Multivariate Analysis Show Similar Results in the Evaluation of Growth and Carcass Traits in Beef Cattle

This research evaluated a multivariate approach as an alternative tool for the purpose of selection regarding expected progeny differences (EPDs). Data were fitted using a multi-trait model and consisted of growth traits (birth weight and weights at 120, 210, 365 and 450 days of age) and carcass traits (longissimus muscle area (LMA), back-fat thickness (BF), and rump fat thickness (RF)), registered over 21 years in extensive breeding systems of Polled Nellore cattle in Brazil. Multivariate analyses were performed using standardized (zero mean and unit variance) EPDs. The k mean method revealed that the best fit of data occurred using three clusters (k = 3) (P < 0.001). Estimates of genetic correlation among growth and carcass traits and the estimates of heritability were moderate to high, suggesting that a correlated response approach is suitable for practical decision making. Estimates of correlation between selection indices and the multivariate index (LD1) were moderate to high, ranging from 0.48 to 0.97. This reveals that both types of indices give similar results and that the multivariate approach is reliable for the purpose of selection. The alternative tool seems very handy when economic weights are not available or in cases where more rapid identification of the best animals is desired. Interestingly, multivariate analysis allowed forecasting information based on the relationships among breeding values (EPDs). Also, it enabled fine discrimination, rapid data summarization after genetic evaluation, and permitted accounting for maternal ability and the genetic direct potential of the animals. In addition, we recommend the use of longissimus muscle area and subcutaneous fat thickness as selection criteria, to allow estimation of breeding values before the first mating season in order to accelerate the response to individual selection.

Analysis of longitudinal data of Nellore cattle from performance test at pasture using random regression model

This study was carried out to estimate (co)variance components and genetic parameters for live weight of Nellore cattle from Performance Test of Young Bulls using random regression models. Data of weights and ages of 925 weaned males was used. The animal model included the fixed effect of contemporary group, age of the animal at weighing as a covariate and as random effects it was considered the effect of additive genetic and permanent environment of the animal. The residue was modeled considering four classes of variances. The models were compared based on the Bayesian information criteria of Akaike and Schwartz. The model polynomial of fourth and sixth order for the direct additive genetic effects and permanent environment of the animal, respectively was the most appropriate to describe the changes in the variances of the weights during the period in which the animals participating in the performance test young bulls. Heritability estimates showed moderate magnitudes and indicated that direct selection will promote improvement of selection criteria adopted. Furthermore, due to high positive correlation between the estimated weights, it was suggested selecting the best animals before at 365 days of age, because it is the period in which the animals have a higher growth rate and thus you can select animals heavier and less delayed.

Caracterização fenotípica de ovelhas dos humedales de ite, sul do peru: dados preliminares

Sheep farming is an important socioeconomic activity in Peru, being one of the main sources of income for many rural families. The objective of the present study was to characterize the phenotype of adult ewes, from local flocks farmed in the Ite Wetlands, southern coast of Peru. These animals were reared in a semi extensive system, on native pastures. Thirteen morphometric traits were measured and analyzed using MEANS, CORR, GLM, DISCRIM and CLUSTER procedures of the statistical program SAS. Three morphologic traits were also registered and three zoometric indices calculated. The results indicated that these ewes are smaller than specialized breeds, but had tendency for meat production and different body sizes, showing variability of biotypes between flocks, according to the management, geographical location and apparent racial miscegenation.

Cattle farmers: profile and speech content analysis while undergoing training to adopt artificial insemination in Goiás State, Brazil

This study was undertaken to verify major issues present in the discourse of cattle farmers when discussing the use of artificial insemination (AI). Seventy-one beef and dairy cattle farmers in the state of Goias, Brazil, were interviewed using semi-structured questionnaires during AI training courses in 2010 and 2011. Data analyses were done using the classic method of textual speech content analysis, performing the pre-analytical, analytical and inferential stages. The written questions were separated in elementary context units (ECU) and sorted into similar thematic groups. These groups originated categories and subcategories, which were nominated based on an a posteriori criteria. Overall, personal motivation was the main issue characterizing discourse by farmers about adoption of AI. This motivation stems from the strong points (highlights) and positive expectations AI offers. The positive expectations were mainly related to perceptions of farmers of animal phenotype improvement rather than to the financial features of cattle production. Basic necessity was the second major issue, with emphasis on work force, infrastructure and animal handling, followed by social influence, with eminence of the institutions and people involved with AI and with the everyday life of cattle farmers. The little emphasis on human resource management and on the use of scientific knowledge may have affected the impact of AI over the years, explaining discreet indices of adoption of AI in Brazil.

Different physiological stages and breeding systems related to the variability of meat quality of indigenous Pantaneiro sheep

This study configures a first report regarding the variability of meat quality of locally adapted Pantaneiro sheep depending on different physiological stages and breeding systems. Pantaneiro sheep are raised in Brazil under a tropical wetland ecosystem denominated Pantanal. Twenty-nine Pantaneiro sheep from different sex and physiological stages were sorted into three groups, simulating three of the most representative ovine meat products commercialized by South American industries: a) non castrated male lambs (n = 11); b) wethers (n = 9); c) cull ewes (n = 9). Animals from each physiological stage were submitted to different breeding systems, resembling farming strategies adopted in several developing countries of South America. The effect of physiological stages on the quality of meat was accessed using 16 variables measured in the longissimus thoracis et lumborum (LM) and the semimembranosus (SM) muscles. The variables were related to brightness, color, physical aspects, soluble and total collagen as well as chemical traits. The physiological stage was defined as a classification variable in order to proceed ANOVA tests and comparison of means (P<0.05). Multivariate analysis was used to identify patterns of similarity and differentiation between samples of different physiological stages (a, b, c). The results revealed that meat quality varies according to different physiological stages, especially between lambs (a) and cull ewes (c). As a consequence, the physiological stage at slaughter should be taken into consideration to cote the quality of meat from indigenous sheep raised in tropical regions. The results contribute towards sensorial evaluation and the characterization of potential food products derived from indigenous sheep bred under tropical climate in developing countries.

Impacto da heterogeneidade de variância residual na avaliação genética de rebanho Nelore no Bioma Amazônia

This study was carried out to evaluate the effects of heterogeneity of residual variance on genetic evaluation of cattle raised on pasture from Amazonia Bioma, Brazil. Adjusted weights at weaning weight (205 days of age) were sorted in three phenotypic classes: low (less than average weight), medium (between the average and the average plus one standard deviation) and high (greater than average plus one standard deviation). There was increased of genetic additive direct and residual variances to the extent that increased phenotypic classes. The heritabilities for low, medium and high phenotypic classes were 0.27, 0.33 and 0.26, respectively. These estimates suggest that mass selection could result in genetic gain on breeding program that use weaning weight as a selection criteria. Genetic correlations between the low and medium, low and high, and medium and high phenotypic classes were 0.82, 0.35 and 0.72, respectively. The estimate of correlation of the breeding values of sire shown effect of the heterogeneity of phenotypic variance on the prediction of animals breeding values. There was a major variability for the breeding values of sires at high phenotype class. Thus, we suggested the identification and selection of sires with the highest breeding values for weaning weight, according with environment in which these animals are being raised.