Sugestão de leitura: confira os artigos publicados pelos membros do GDMA
Postado em 31/out/2019
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Artigo 1: Genetic evaluation for days to calving in Nellore heifers using Exponential and Gaussian Censored Bayesian models
Autores: Pedro Vital Brasil Ramos, Fabio Luiz Buranelo Toral, Fabyano Fonseca e Silva, Talita Estéfani Zunino Santana, Tulio Vilar Vilas Boas Oliveira, Daniele Botelho Diniz Marques, Luiz Fernando Brito
Revista: Livestock Science (2019)
Abstract: Days to calving (DC) plays a key role in the overall profitability and long-term sustainability of tropically-adapted beef cattle breeds (e.g. Nellore), especially those raised under extensive production systems. However, some females usually do not have reliable phenotypic records because of late calving and even failures in its recording, which can be considered as censored data. Furthermore, DC tends to present an asymmetric distribution (such as Exponential) as it represents the time to an event occurrence, i.e., calving. Thus, we aimed to propose and evaluate the Exponential censored Bayesian models for genetic evaluation of DC in Nellore cattle as well as to perform comparison analysis (predictive ability and goodness-of-fit) with the conventional Gaussian models. Additionally, different scenarios were based on censoring definition according to the cut-off values: 321, 351 and 381 DC. The predictive ability was evaluated under a cross-validation approach, and the goodness-of-fit were performed using the Deviance Information Criterion (DIC). Gaussian models presented higher predictive ability and lower DIC (better goodness-of-fit) compared to Exponential models. Censored models provided higher predictive ability than uncensored models. The highest predictive performance was observed for Gaussian models, which also reported more realistic heritability estimates (ranging from 0.03 to 0.23). Additionally, Spearman correlations and coincidence rates were higher between different censored scenarios in Gaussian models. The inclusion of censored data into genetic evaluations could be recommended for Gaussian models, and the proposed Exponential model was not suitable for genetic evaluations of DC.
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Artigo 2: Bayesian linear-threshold censored models for genetic evaluation of age at first calving and stayability in Nellore cattle
Autores: Edson V. Costa, Henrique T. Ventura, Renata Veroneze, Fabyano F. Silva, Mariana A. Pereira, Paulo S. Lopes
Revista: Livestock Science (2019)
Abstract: We aimed to evaluate multiple-trait Bayesian models for handling censored records in genetic evaluations of age at first calving (AFC) and stayability (STAY) in Nellore cattle. Phenotypic and pedigree datasets were provided by Brazilian Association of Zebu Breeders. Four models were evaluated: linear-threshold model (LTM), penalty-threshold model (PTM), modified penalty-threshold model (MPTM) and linear-threshold-threshold model (LTTM). Predictive ability of the models was compared using cross-validation analysis. The validation population was composed by the youngest individuals with both parents known and phenotyped for AFC. Pearson’s correlations between predict breeding values of the validation population with and without phenotypic information were computed. Percentages of animals selected in common among percentiles 1% and 10% were also calculated. In general, the correlations between predicted breeding values were high in magnitude, being the highest one observed for LTM (0.89). The heritability estimates (posterior mean) for AFC presented low magnitude and ranged from 0.02 (PTM and MPTM) to 0.07 (LTM); as well as the heritability estimates for STAY (0.09 to 0.16). The genetic correlations between AFC and STAY ranged from −0.23 to −0.51, being the highest one observed when using PTM. The inclusion of censored records in the genetic evaluation increased the residual variances. Genetic correlations between traits were not substantially influenced by the inclusion of censored data. In addition, the linear-threshold model without censored data presented the best predictive ability, thus we recommend this model for genetic evaluation of age at first calving and stayability in Nellore cattle.
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Artigo 3: Genetic parameters for fertility traits in Nellore bulls
Autores: Ivan Carvalho Filho, Daniele Botelho Diniz Marques, Carolina Filardi de Campos, José Domingos Guimarães, Simone Eliza Facioni Guimarães, Paulo Sávio Lopes, Fabyano Fonseca e Silva, Renata Veroneze
Revista: Reproduction in Domestic Animals (2019)
Abstract: Nellore is the main cattle breed used in Brazil, being the largest commercial herd in the world. Beyond the importance of male reproductive efficiency for farm profit, the use of reproductive techniques, mainly artificial insemination, turns the evaluation of male reproductive traits even more important. Estimation of genetic parameters increases the knowledge on traits variances and allows envisaging the possibility of the inclusion of new traits as selection criterion. Genetic parameters for fifteen traits, that can be classified as testicular biometry or physical and morphological semen traits, were estimated for a Nellore bull population ranging from 18 to 36 months. Single trait and bi‐trait animal models were used for (co)variance components estimation. The contemporary group was considered as fixed effect and age at measurement as covariable. Scrotal circumference presented heritability of 0.47 ± 0.12. This value is similar to the heritabilities found for all testicular biometry traits (0.34 to 0.48). Sperm progressive motility, which has a direct effect on bull fertility, presented low heritability (0.07 ± 0.08). Major and total sperm defects presented moderate to high heritabilities (0.49 ± 0.18 and 0.39 ± 0.15, respectively), indicating that great genetic gain can be obtained through selection against sperm defects. High and positive genetic correlations were observed among testicular biometry traits, which also presented favorable genetic correlations with physical and morphological traits of the semen with magnitude ranging from high to low. Scrotal circumference presented moderate to high and favorable genetic correlations with sperm progressive motility, sperm turbulence, major sperm defects and total sperm defects. Thus, the selection for scrotal circumference results on favorable correlated genetic response for semen quality. The results show that the use of scrotal circumference as reference trait for bull fertility is appropriate, since it presents high heritability and favorable genetic correlation with semen quality.