[Show abstract][Hide abstract] ABSTRACT: Genetic breeding programs of beef cattle in Brazil are including new features, mainly related to reproductive efficiency. Thus, it is necessary to study the effectiveness of selection and quantify genetic gain for these traits in herds. This study estimated genetic and phenotypic parameters and genetic trends for reproductive traits used in breeding programs for Nelore beef cattle. The traits studied were the scrotal circumference (SC) at 365 and 450 days of age (SC365 and SC450), age at first calving (AFC) and gestation length, as a cow trait (GLcow) and a calf trait (GLcalf). The (co)variance components were obtained with the Restricted Maximum Likelihood Methodology in a single and double-trait analysis of the animal model. For scrotal circumference (SC365 and SC450), positive and favorable genetic gains were observed. For AFC, GLcow and GLcalf, the trends were favorable for selection, but without significant genetic gain. Selection for large SC may reduce AFC and improve female reproductive efficiency. The selection for reproductive traits (SC365, SC450, AFC and GL) may improve reproductive and productive efficiency of Nelore cattle, if used as a selection criterion.
Ciência e Agrotecnologia 07/2015; 39(4):355-362. DOI:10.1590/S1413-70542015000400006 · 0.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Objetivou-se estimar as herdabilidades para as características de carcaça de área de
olho de lombo (AOL), espessura de gordura subcutânea (EG) e espessura de gordura
subcutânea na garupa (EGP8), medidas por ultrassonografia, em bovinos da raça Nelore
Mocho, criados em bioma Cerrado. As informações utilizadas foram provenientes de
criatórios da raça Nelore Mocho, participantes do Programa Nelore Brasil, da
Associação Nacional de Criadores e Pesquisadores (ANCP), localizados nos estados que
representam as maiores áreas contínuas do bioma Cerrado. As estimativas de
herdabilidade foram obtidas mediante análises bi-características, sob modelo animal,
utilizando a estatística bayesiana por meio do aplicativo MTGSAM. As estimativas de
herdabilidade foram de média magnitude para a AOL (0,25), EG (0,19) e EGP8 (0,25). Os
resultados obtidos sugerem que as características de carcaça, avaliadas por
ultrassonografia, apresentam grande variabilidade genética e podem ser incluídas em
programas de melhoramento genético de bovinos da raça Nelore Mocho.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to estimate variance and covariance components for gestation length (GL), birth weight (BW), weaning weight (WW), and accumulated productivity (ACP), and their respective genetic trends for Nellore cattle raised in Brazil. The ACP trait is a reproduction index developed by the National Association of Breeders and Researchers (ANCP) and comprises the total number of calves born per dam, weight of weaned calves, and age of the dam at calving. A total of 25,085, 46,911, 50,044, and 7,351 observations were considered to analyze GL, BW, WW, and ACP. Genetic parameters were estimated by the Average Information Restricted Maximum Likelihood method in single and two-trait analyses. The average direct heritability estimates obtained in two-trait analyses were equal to 0.38±0.03 (GL), 0.25±0.02 (BW), 0.28±0.02 (WW), and 0.11±0.02 (ACP). The highest genetic correlation was found between BW and WW (0.36±0.05), followed by BW and ACP (0.20±0.09), and BW and GL (0.19±0.06). Significant direct genetic trends (P<0.001) were observed for GL, BW, and WW; equal to -0.027 days per year, 0.073 kg per year, and 0.8456 kg per year, respectively. Greater emphasis should be given to accumulated productivity and gestation length traits in order to increase the number and weight of weaned calves. As accumulated productivity presents low heritability estimates, genetic improvement through selection could be slow in the Nellore breed. Our study reports genetic progress for weaning weight, since its genetic trend has increased over the years. Similar genetic trend for birth weight was observed, which may be a consequence of selection towards higher body weights at older ages.
[Show abstract][Hide abstract] ABSTRACT: Selection in heterogeneous environments has had increasing importance since production system definition is linked to economic instability and climatic changes. The aim of this work was to compare environmental sensitivity between sexes and along development. Data were collected in 366 Brazilian herds for the Brazilian Nelore Cattle Breeding Program with 1,110,662 body weights from 408,416 animals. Eight different analyses were applied using a principal component analysis of the cubic polynomial random regression coefficients' estimates, with a sex-separated developmental reaction norm approach. Results showed different estimated eigenvalues for coefficients of different orders in different sexes. Eigenvalues of level and slope coefficients explained a great majority of the variation of Nelore beef cattle weight in Brazilian production systems, with a distinguished increase of slope coefficient eigenvalue in female analyses along the age axis when compared to male analyses.
10th World Congress of Genetics Applied to Livestock Production; 08/2014
[Show abstract][Hide abstract] ABSTRACT: Genetic parameters for ultrasound carcass and growth traits were estimated by factor analyses used as a special case of structural equation models in a Bayesian framework. Data were analyzed using the standard multi-trait mixed models with sire model (Model 1; SMTMs). The factor analyses (FA) were done by four alternative FA models. The results indicate that FA models could estimate breeding values of the bulls practically equal relative to the SMTMs. The FA models may reduce the ranking model and give a parsimonious estimation of genetic covariance matrices. Although the FA models may reduce covariance matrices ranks and give a parsimonious estimation of dispersion parameters, these models have to be tested in order to implement the benefits, as an alternative of SMTMs. INTRODUCTION The continuous increasing of records and traits in genetic evaluation schemes for beef cattle generally involve multi-trait mixed models analyses, which requires genetic links among these traits. It leads to statistical and computational difficulties in estimating the genetic (co)variance matrix needed to have accurate breeding values. Structural equation models (SEM, e.g., Wright 1921) are multivariate models adapted to obtain more parsimonious quantitative genetic mixed-effects models (Gianola and Sorensen (2004)). SEM can be understood like a term that does not denote a particular statistical technique, but a number of techniques and procedures used together aiming to model some covariance structure. In animal breeding, specifically in this paper, SEM was used to model the estimated genetic and residual (co)variance matrix. These models can be viewed as an extension of the standard multi-trait mixed models (SMTM, e.g., Henderson and Quaas (1976)) that are capable of expressing functional networks among traits. Gianola and Sorensen (2004) discussed the use of recursive and simultaneous equation models (special case of SEM) acting on phenotypes. Alternatively, the Factor Analysis (FA) may be used as another special case of SEM to represent the genetic covariance matrix (Jӧreskog (1970)). FA can be used to model genetic effects in the context of a multivariate linear mixed model for reducing the dimension of the estimated genetic (co)variance matrix, obtaining a more parsimonious model without reducing dimension of the original records (e.g., de los Campos and Gianola (2007)). The objective of this study was to consider FA (a special case of SEM) acting on genetic and residual effects separately to estimate genetic and residual (co)variance parameters modeling traits and estimating genetic parameters in genetic improvement of Brazilian Nelore beef cattle.
World Congress of Genetics Applied to Livestock Production, Vancouver; 08/2014
[Show abstract][Hide abstract] ABSTRACT: Beef cattle producers in Brazil use body weight traits as breeding program selection criteria due to their great economic importance. The objectives of this study were to evaluate different animal models, estimate genetic parameters, and define the most fitting model for Brahman cattle body weight standardized at 120 (BW120), 210 (BW210), 365 (BW365), 450 (BW450), and 550 (BW550) days of age. To estimate genetic parameters, single-, two-, and multi-trait analyses were performed using the animal model. The likelihood ratio test was verified between all models. For BW120 and BW210, additive direct genetic, maternal genetic, maternal permanent environment, and residual effects were considered, while for BW365 and BW450, additive direct genetic, maternal genetic, and residual effects were considered. Finally, for BW550, additive direct genetic and residual effects were considered. Estimates of direct heritability for BW120 were similar in all analyses; however, for the other traits, multi-trait analysis resulted in higher estimates. The maternal heritability and proportion of maternal permanent environmental variance to total variance were minimal in multi-trait analyses. Genetic, environmental, and phenotypic correlations were of high magnitude between all traits. Multi-trait analyses would aid in the parameter estimation for body weight at older ages because they are usually affected by a lower number of animals with phenotypic information due to culling and mortality.
Tropical Animal Health and Production 07/2014; 46(7). DOI:10.1007/s11250-014-0640-3 · 0.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The objective of the present study was to analyze the phenotypic inter-relationships between growth, feed intake and carcass traits in polled Nellore cattle, as well as to determine which bulls produced the most efficient progeny. The experiment was conducted in the feedlot of the Guaporé Pecuária (Livestock) Company, OB Brand. The following traits were analyzed: initial live weight (ILW); final live weight (FLW); average daily gain (ADG); dry matter intake (DMI); gain:feed (G:F); residual feed intake (RFI); rib-eye area (REA); rump fat thickness (RF); backfat thickness at the 12th-13th rib (BF); weighted fat score (WF); and intramuscular fat percentage (IMF). Both univariate and multivariate analyses were performed to analyze the inter-relationships between the studied traits. No significant phenotypic associations were observed between growth, carcass traits and residual feed intake, while the correlation between RFI and G:F was negative. Therefore, RFI may be used to select more nutritionally efficient animals without compromising growth or adult size. The selection of bulls with progeny showing low residual feed intake is recommended, as selection for low RFI tends to improve feed efficiency without compromising growth and development.
Revista Ciencia Agronomica 03/2014; 45(1):168-176. DOI:10.1590/S1806-66902014000100020 · 0.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
PLoS ONE 09/2013; 8(9):e75423. DOI:10.1371/journal.pone.0075423 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The objectives of this study were to estimate genetic parameters and genetic trends for traits evaluated by the Guzera Breeding Program (PAGRG), in order to provide support for the genetic improvement of the breed. Records on 18,491 animals from 43 farms were used. Traits studied were rib eye area (REA), fat thickness between the 12th and 13th rib (FT), rump fat thickness (RF), age at first calving (AFC), scrotal circumference at 365 (SC365) and 450 (SC450) days of age, gestation length (GL), mature weight of the cow (MWC), body weight at birth (BWB), 120 (BW120), 210 (BW210), 365 (BW365), 450 (BW450 days old) and cumulative productivity in females (CP). Genetic parameters and breeding values were estimated by restricted maximum likelihood, by one and two-trait analysis whose general model included additive genetic random effect and fixed effect of contemporary groups (CG), for CP, AFC, SC365 and SC450. For GL, BWB, BW120, BW210, BW365 and BW450, a maternal additive random genetic effect and the fixed effect (linear and quadratic) of the cow's age at calving were added to the base model. For carcass traits, the fixed effect (linear) of weight at ultrasound was included. Genetic trends were obtained by linear regression of average annual breeding values (obtained by one-trait analysis) on year of birth (1987 to 2009) The t statistic was used and the null hypothesis considered the regression coefficient as zero. Most traits showed sufficient additive genetic variation, except CP, FT and RF, which expressed low genetic correlations with other traits. The trend graphs indicate that genetic change is occurring in the average breeding value of animals over time, with the exception of CP, GL and the maternal genetic effect for BWB. The inclusion of RF in a selection index proposed by ANCP is recommended. How to cite this abstract: J. Dairy Sci. 96(E-Suppl. 1):[page number]. or J. Anim. Sci. 91(E-Suppl. 2):[page number]. To locate the page number, refer to the 2013 Abstract Book here:
ADSA - ASAS Joint Annual Meeting, Indianapolis, Indiana, USA; 07/2013
[Show abstract][Hide abstract] ABSTRACT: The objective of this study was to estimate genetic parameters for female mature weight (FMW), age at first calving (AFC), weight gain from birth to 120 days (WG_B_120), from 210 to 365 days (WG_210_365), rib eye area (REA), back fat thickness (BF), rump fat (RF) and body weight at scanning date (BWS) using single and multiple-trait animal models by the REML method from Nellore cattle data. The estimates of heritability ranged from 0.163±0.011 for WG_210_365 to 0.309±0.028 for RF using the single-trait model and from 0.163±0.010 for WG_210_365 to 0.382±0.025 for BWS using the multiple-trait model. The estimates of genetic correlations ranged from −0.35±0.08 between AFC with BF to 0.69±0.04 between WG_B_120 with BWS. Selection for weights gains, REA, and BWS can improve FMW.
[Show abstract][Hide abstract] ABSTRACT: Com o objetivo de se comparar o ajustamento de modelos com diferentes definições de grupos contemporâneos sobre as estimativas de (co)variâncias e parâmetros genéticos para pesos padronizados e reais aos 120 e 210 dias de idade, analisaram-se dados de 72.731 bezerros Nelore, machos e fêmeas, nascidos de 1985 a 2005 em 40 rebanhos integrantes do PMGRN - Nelore Brasil. Foram comparados quatro modelos incluindo diferentes estruturas de grupos contemporâneos (CG), julgados pelos critérios de informação de Akaike, Bayesiano e modificado de Akaike. As estimativas foram obtidas pelo método da máxima verossimilhança restrita livre de derivadas. As estimativas de (co)variâncias e parâmetros genéticos foram similares entre os modelos, porém os critérios de informação (BIC, CAIC) indicaram que o modelo mais adequado é o que considera o grupo contemporâneo como efeito aleatório, sendo este constituído pela concatenação dos efeitos de rebanho, ano de nascimento, grupo de manejo e efeito sazonal de trimestre de nascimento, e com efeito do sexo do bezerro independente do CG.
[Show abstract][Hide abstract] ABSTRACT: Objetivou-se analisar a interação genótipo-ambiente sobre os pesos aos 120 e 210 dias de bovinos da raça Nelore, criados a pasto, nos Estados do Maranhão, Mato Grosso e Pará. O estudo foi realizado utilizando-se de dados de campo da raça Nelore cedidos pelo Programa de Melhoramento Genético da Raça Nelore (PMGRN-ANCP), totalizando 37.032 animais registrados desde 1993 a 2010. As estimativas médias e desvios padrão para pesos padronizados aos 120 dias (P120), e aos 210 dias (P210) de idade para os estados do MA, MT e PA foram de 123,43±17,06; 133,91±19,62; 130,07±16,03kg (P120), 181,83±34,15; 194,73±28,52; 189,76±23,45kg (P210), respectivamente. As correlações genéticas entre os desempenhos das progênies de um mesmo reprodutor nos diferentes estados variaram de 0,42 (Maranhão-Mato Grosso), 0,38 (Maranhão-Para) a 0,70 (Mato Grosso-Para) para P120; de 0,49 (Maranhão-Mato Grosso), 0,13 (Maranhão-Para) a 0,40 (Mato Grosso-Para) para P210. As menores correlações genéticas, em ambas as características estudadas, foram observadas entre Maranhão e Pará, estados com condições de ambiente mais contrastante. Estes resultados denotam a existência de interação genótipo-ambiente, tanto no peso aos 120 dias quanto no peso aos 210 dias de idade, o que influenciou diretamente a predição do valor genético dos reprodutores, resultando em classificação diferente de um mesmo touro em cada estado. Portanto, faz-se necessário mais bem estudar inclusão desta interação nos modelos de avaliação genética dos animais, pois a seleção e reprodução do melhor touro apresentarão impactos econômicos distintos em cada estado e influenciará a tomada de decisão dos criadores.