Cláudio Ulhôa Magnabosco

Análise genética de escores de avaliação visual de bovinos com modelos bayesianos de limiar e linear

The objective of this work was to compare the estimates of genetic parameters obtained in single- trait and two-trait bayesian analyses, under linear and threshold animal models, considering categorical morphological traits of bovines of the Nelore breed. Data of musculature, physical structure and conformation were obtained between years 2000 and 2005, from 3,864 bovines of the Nelore breed from 13 participant farms of the Nelore Brazil Program. Single-trait and two-trait bayesian analyses were performed under linear and threshold animal models. In general, the linear and threshold models were efficient in estimating genetic parameters for visual scores under single-trait bayesian analyses. In the two-trait analyses, it was observed that: using continuous and categorical data, the threshold model provided greater estimates of genetic correlation than those of the linear model; with categorical data, the heritability estimates were similar. One major advantage of the linear models was its smaller requirements in the analyses processing time. In the genetic evaluation of animals for visual scores, the use of the linear or threshold model did not influence the classification of the animals, based on their predicted breeding values, which suggests that both models can be used in genetic improvement programs.

Structure and genetic variability in Nellore (Bos indicus) cattle by pedigree analysis

Parameters based on the probability of gene origin were used to describe the genetic variability in strains of Nellore and polled Nellore (Bos indicus) cattle that participated in the Program for Genetic Improvement of the Nellore Breed (Programa de Melhoramento Genetico da Raca Nelore). The effective number of founders was 87.2 for Nellore and 107.9 for polled Nellore, while the number of ancestors was 59.8 for Nellore and 61.5 for polled Nellore and the remaining genomes were 39.4 for Nellore and 34.5 for polled Nellore cattle. The results indicate an intense use (by artificial insemination) of some sires and the absence of subdivisions in the population. The family structure in the two breeds was mainly caused by the genetic contribution of the same sires and only mating preferences for descendants of some founders are recorded in either breed. The results suggest that genetic variability needs monitoring in order to avoid the compromise of genetic improvement in economically important traits in the breeding program.

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.

Genetic correlations between categorical morphological traits in Nelore cattle by applying Bayesian analysis under a threshold animal model

In this study, Bayesian analysis under a threshold animal model was used to estimate genetic correlations between morphological traits (body structure, finishing precocity and muscling) in Nelore cattle evaluated at weaning and yearling. Visual scores obtained from 7651 Nelore cattle at weaning and from 4155 animals at yearling, belonging to the Brazilian Nelore Program, were used. Genetic parameters for the morphological traits were estimated by two-trait Bayesian analysis under a threshold animal model. The genetic correlations between the morphological traits evaluated at two ages of the animal (weaning and yearling) were positive and high for body structure (0.91), finishing precocity (0.96) and muscling (0.94). These results indicate that the traits are mainly determined by the same set of genes of additive action and that direct selection at weaning will also result in genetic progress for the same traits at yearling. Thus, selection of the best genotypes during only one phase of life of the animal is suggested. However, genetic differences between morphological traits were better detected during the growth phase to yearling. Direct selection for body structure, finishing precocity and muscling at only one age, preferentially at yearling, is recommended as genetic differences between traits can be detected at this age.

Bayesian inference in genetic parameter estimation of visual scores in Nellore beef-cattle

The aim of this study was to estimate the components of variance and genetic parameters for the visual scores which constitute the Morphological Evaluation System (MES), such as body structure (S), precocity (P) and musculature (M) in Nellore beef-cattle at the weaning and yearling stages, by using threshold Bayesian models. The information used for this was gleaned from visual scores of 5,407 animals evaluated at the weaning and 2,649 at the yearling stages. The genetic parameters for visual score traits were estimated through two-trait analysis, using the threshold animal model, with Bayesian statistics methodology and MTGSAM (Multiple Trait Gibbs Sampler for Animal Models) threshold software. Heritability estimates for S, P and M were 0.68, 0.65 and 0.62 (at weaning) and 0.44, 0.38 and 0.32 (at the yearling stage), respectively. Heritability estimates for S, P and M were found to be high, and so it is expected that these traits should respond favorably to direct selection. The visual scores evaluated at the weaning and yearling stages might be used in the composition of new selection indexes, as they presented sufficient genetic variability to promote genetic progress in such morphological traits.

Genótipo e condição sexual no desempenho e nas características de carcaça de bovinos de corte superjovens

Ninety-six young beef males were allotted to a completely randomized design in a 4x3 factorial scheme, four genetic groups, Nellore (N), ½ Simmental ½ Nellore (SN), ½ Red Angus ½ Nellore (AN) and ½ Red Angus ¼ Simmental ¼ Nellore (ASN), and three sex conditions (SC), intact (I), castrated (C) and castrated plus Synovex S ® implant (CS). Males were castrated at six months of age, and feedlot started two months later, with the animals being fed with a 70% chopped sugar cane : 30% concentrate diet. Steers were weighted with 28 days intervals, after 16 hours fastening, and were slaughtered with 13 to 15 month of age. The statistical analyses were performed with the MINITAB program. The effects of genotype (G), SC and G x SC on performance and carcass characteristics, were evaluated. Slaughter (SW) and hot carcass weight (HCW) were affected by G. The SN presented the highest SW (389.3 kg) and AN the lowest (343.1 kg). SC affected SW, HCW and finishing degree (FD). I and CS males were heavier at slaughter (373.8 and 375.2 kg, respectively) than C (341,2 kg). The lowest HCW was observed for C steers (180,6 kg), differing (P<.02) from I (197 kg) and CS (201,3 kg). CS steers showed better FD (2,17 points) than the other SC. The SC showed tendency (P< .07) to influence ribeye area, with CS steers showing larger area (65.2 cm2). The G x SC interaction was significant for average daily gain and carcass dressing percentage. When adjusted for initial weight, the interaction was significant for SW, and when adjusted for SW the interaction was significant for HCW. The Simmental crosses were heavier at slaughter. Castration at six months reduced the feedlot performance of young males. The Synovex S® implant increased the finishing degree of the castrated steers carcasses.

Estimativas de correlações genéticas entre escores visuais e características de carcaça medidas por ultrassonografia em bovinos Nelore utilizando modelos bayesianos linear-limiar

The objective of this study was to estimate the genetic correlations between visual scores and the carcass traits measured by ultrasound, in Nellore breed cattle, using the bayesian statistics by Gibbs Sampling, in the linear-threshold model. The morphological categorical traits of musculature, physical structure, conformation and sacrum were studied, evaluated at 15 and 22 months. The carcass traits of the longissimus muscle area, backfat thickness, rump fat thickness and hip height were evaluated. Visual scores should be used as selection criterion to increase genetic progress for the longissumus muscle area. The estimates of genetic correlations obtained between musculature and backfat thickness and rump fat thickness indicated that the selection for musculature may lead to animals with better carcass finishing. Selection for physical structure and conformation, at 15 and 22 months, should promote response correlated with the hip height.

Efeitos da endogamia sobre características de reprodução, crescimento e valores genéticos aditivos de bovinos da raça Pardo-Suíça

Inbreeding effects on calving interval (CI), birth weight (BW), weaning weight (WW) and on the direct and maternal breeding values for BW were evaluated in a purebred Brown Swiss herd raised in northeast Brazil. Data were collected from 1946 to 1993. Inbreeding coefficients (F) were estimated according to Wright method using the MTDFREML package. Breeding values were predicted by a BLUP animal model that included fixed effects of sex, month and year of birth, parity of dam and direct and maternal inbreeding as covariate. The relationship matrix included 1209 animals and the average and maximum inbreeding were 12.50% and 38.30% respectively. In general, increases in inbreeding levels were followed by reductions on direct breeding value for BW. Of the total variance, direct effects for BW accounted for 47% and maternal effects for 40%. For CI, the effects of sire of dam, parity of dam and year of birth were significant, and the regression coefficient of CI on direct inbreeding was 1.4. For BW, the effects of year of birth within period, sex, age of dam and linear and quadratic inbreeding of calf were significant. The effect of year of birth was significant for WW. Regression coefficient of WW on maternal inbreeding was -0.51±0,14 kg.

Avaliação genética de características de escores visuais de bovinos da raça Nelore da desmama até a maturidade

Os objetivos neste estudo foram estimar parâmetros geneticos das caracteristicas categoricas musculosidade, estrutura fisica, aspectos raciais, conformacao, onfalo, pigmentacao e sacro e predizer os valores geneticos utilizando-se a estatistica bayesiana sob modelo animal de limiar, considerando diferentes idades de bovinos da raca Nelore. As informacoes de escores visuais foram obtidas nos anos de 2000 a 2005 de bovinos provenientes de 13 fazendas participantes do Programa Nelore Brasil. Nas analises bicaracteristicas, foram utilizados 500.000 ate 1.100.000 ciclos para alcancar a convergencia da cadeia de Gibbs. O descarte inicial e o intervalo amostral foram de 100.000 e 1.000 ciclos, respectivamente. As caracteristicas de escores visuais avaliadas aos 8 e 22 meses de idade apresentaram estimativas de herdabilidades moderadas, indicando resposta rapida a selecao direta. Os escores visuais indicaram possibilidade de resposta rapida a selecao direta e, portanto, devem ser incorporados em programas de melhoramento genetico como criterios de selecao. As estimativas de correlacoes geneticas entre musculosidade, estrutura fisica e conformacao tambem indicam que a selecao direta para uma destas caracteristicas trara progresso genetico as outras. Recomenda-se utilizar os escores visuais como criterios de selecao em pelo menos duas fases de vida do animal, na desmama e ao sobreano.

Análise bayesiana na estimação de correlações genéticas entre escores visuais e características reprodutivas de bovinos Nelore utilizando modelos linear-limiar

The genetic correlations between visual scores and reproductive traits, using the bayesian statistic under the linear-threshold animal model, in bovines of the Nelore breed were estimated. Categorical morphological traits were also evaluated at eight, 15, and 22 month-old, concerning musculature, physical structure, conformation and sacrum, the escrotal circumferences measured at the ages of 365 and 450-day-old, and the age at first calving. The estimates of genetic correlations were moderates, suggesting that the selection of animals with better morphological conformation may lead to animals more precocious and with greater fertility. The estimates of genetic correlation concerning the escrotal circumference at 450 day-old and the age at first calving with the evaluated visual scores at 22 month-old were higher than the ones obtained between visual scores at eight and 15 month-old. The use of these visual scores as a criterion of selection may also bring genetic progress to the reproductive traits.