Estimates of genetic parameters for visual scores and daily weight gain in Brangus animals.

(Co)variance components were estimated for visual scores of conformation (CY), early finishing (PY) and muscling (MY) at 550 days of age (yearling), average daily gain from weaning to yearling (GWY), conformation (CW), early finishing (PW) and muscling (MW) scores at weaning, and average daily gain from birth to weaning (GBW) in animals forming the Brazilian Brangus breed born between 1986 and 2002 from the livestock files of GenSys Consultants Associados S/C Ltda. The data set contained 53 683; 45 136; 52 937; 56 471; 24 531; 21 166; 24 006 and 25 419 records for CW, PW, MW, GBW, CY, PY, MY and GWY, respectively. Data were analyzed by the restricted maximum likelihood method using single- and two-trait animal models. Direct heritability estimates obtained by single-trait analysis were 0.12, 0.14, 0.13 and 0.14 for CY, PY and MY scores and GWY, respectively. A positive association was observed between the same visual scores at weaning and yearling, with correlations ranging from 0.64 to 0.94. Estimated correlations between GBW and weaning and yearling scores ranged from 0.60 to 0.77. The genetic correlation between GBW and GWY was low (0.10), whereas correlations of 0.55, 0.37 and 0.47 were observed between GWY and CY, PY and MY, respectively. Moreover, GWY showed a weak correlation with CW (0.10), PW (-0.08) and MW (-0.03) scores. These results indicate that selection of the traits that was studied would result in a small response. In addition, selection based on average daily gain may have an indirect effect on visual scores as the correlations between GWY and visual scores were generally strong.

Proposta de metodologia para a conversão do escore de avaliação visual de conformação em escore de estrutura, em bovinos de corte / Proposal of methodology for converting visual score of conformation into visual score of structure for beef cattle

A adoção de dois sistemas de avaliação visual por diferentes programas de melhoramento de bovinos de corte no Brasil torna necessário o desenvolvimento de uma metodologia capaz de compará-los. Foram analisados 1.567 e 1.095 registros referentes aos escores de avaliação visual de conformação (C) e estrutura (E), respectivamente, de touros jovens submetidos à prova de desempenho, pertencentes a vinte e uma raças/grupos genéticos com aptidão para corte. Os escores foram atribuídos por três técnicos, sendo o escore final a média aritmética destes. Conceitualmente, o escore de C leva em conta a musculatura do animal, o que não ocorre com o escore de E. Foram feitas análises de correlação para determinar o grau de associação entre os escores Ce E com o escore de musculatura (M), usando grupo de contemporâneos (raça, ano, local de prova e curral) como efeito fixo. Uma vez determinada esta associação, foi calculado um fator de correção capaz de converter C em E mediante desconto da avaliação de M embutida em C. A seguir, esta metodologia foi aplicada a 866 e 467 registros referentes aos escores de avaliação visual de conformação (C) e estrutura (E), respectivamente, de touros jovens submetidos à prova de desempenho da raça Nelore. A metodologia proposta permitiu a conversão do escore de C em escore de E. Os resultados mostraram que o escore E tendeu a distribuir melhor as notas dentro do grupo avaliado que o escore C.

The use of two systems for visual score avaliation in beef cattle breeding programs causes difficulties to compare animals evaluated by them. We analyzed 1,567 and 1,095 records on visual scores of conformation (C) and structure (E), respectively, of young bulls submitted to performance test from twenty-one breeds and/or genetic groups in order to determine a way of converting these two scores. The scores were attributed by three technicians, being the final score the arithmetic mean of the three notes. Conceptually, C takes into account the musculature of the animal, which does not occurre with E. So correlation analysis were performed in order to determine the degree of association between the scores C and E with the muscling score (M) using contemporary group (breed, year, place and curral of test) as a fixed effect. Then a correction factor for converting C into E by discounting the effect of M embedded in C could be estimated. The next step was to apply this methodology on 866 and 467 records of visual scores of conformation (C) and structure (E), respectively, of Nellore young bulls submitted to a performance test The proposal methodology was able to convert C into E. The results showed the score E distributes the notes better than the score C.

Estimativas de correlações genéticas entre características de carcaça medidas por ultrassonografia e por escores visuais em touros Brangus / Genetic correlation estimates between carcass traits measured by ultrasonography and by visual scores in Brangus bulls

Atualmente, a qualidade da carne bovina vem sendo requisitada por frigoríficos e consumidores, assim como, técnicas de avaliar a carcaça de animais vivos tem sido implementadas. Foram analisados 151 registros referentes às diferenças esperadas na progênie (DEPs), obtidas por um modelo animal reduzido, de escores visuais de musculatura (M) e precocidade (P) e de medidas por ultrassonografia bidimensional em tempo real: área de olho de lombo (AOL), marmoreiro (MARM) e espessura de gordura subcutânea (EGS). Foram estimadas correlações de Pearson entre as DEPs de M e AOL, P e EGS e P e MARM. A AOL apresentou correlação moderada com M, a correlação entre P e EGS foi também moderada e entre P e MARM foi de pequena magnitude, para a raça Brangus. Espera-se que a seleção para M apresente resposta correlacionada moderada e positiva em AOL, que a seleção para P resulte em resposta correlacionada moderada e positiva em EGS e que a seleção para P traga pouco incremento em MARM.

Meat quality has been demanded by consumers and industry, such as, techniques to measure carcass traits in live animals have been applied. We analyzed 151 records on expected breeding values (DEPs) of Brangus bulls, predicted using a reduced animal model, for the visual scores of muscling (M) and early finishing (P) and for the carcass measures by ultrasound bi-dimensional real-time: backfat thickness (EGS), marbling (MARM) and rib eye area (AOL). Pearson's correlations were estimated between DEPs of M and AOL, P and EGS and P and MARM. AOL showed moderate correlation with M, the correlation between P and EGS was also moderate and between P and MARM was weak for Brangus breed. It is expected that the selection applied on M presents positive and moderate correlated response on AOL. The selection for P would result in moderate and positive correlated response on EGS and that the selection for P would result in moderate increase in P.

GENETIC AND PHENOTYPIC ESTIMATES OF VISUAL SCORES AND AVERAGE DAILY GAIN FROM BIRTH TO WEANING OF CATTLE USED TO FORM THE BRANGUS BREED. / ESTIMATIVAS DE PARÂMETROS GENÉTICOS E FENOTÍPICOS DE ESCORES VISUAIS E DE GANHO MÉDIO DE PESO DO NASCIMENTO A DESMAMA DE BOVINOS FORMADORES DA RAÇA BRANGUS.

      The aims of this study were to estimate genetics parameters for visual scores of conformation (C), precocity (P) and musculature (M), measured at weaning and average daily gain from birth to weaning(GND) of animals used to form the Brangus breed, born from 1986 to 2002. Data was provided by Gensys Consultores Associados S/C Ltda.. The data set had 53,683, 45,136, 52,937 and 56,471 records on C, P, M and GND. The data were analyzed by restrict maximum likelihood method using animal models. The general model included the fixed effects of contemporary group, the age of cow at calving and the age of calf at weaning (linear and quadratic) and individual heterozygosis and the genetic direct effect, the maternal genetic effect and the permanent environmental effect as random. The direct heritabilities estimated using uni trait analyses were 0.17, 0.15, 0.15 and 0.18, respectively, for C, P, M and GND. The genetic correlations estimated to visual scores performing bi-trait analyses showed positive association with genetics correlations between 0.92 and 0.96. The genetic correlations estimated between GND and the visual scores showed values between 0.65 and 0.81. These results indicate that selection for visual scores and GND at weaning could be applied for these traits and also should result in indirect selection response for average daily weight,

Foram estimados parâmetros genéticos para os escores visuais de conformação (C), precocidade (P) e musculatura (M) e ganho de peso médio diário do nascimento à desmama (GND) de animais formadores da raça Brangus, nascidos entre 1986 e 2002, cujos dados provieram do arquivo zootécnico da empresa Gensys Consultores Associados S/C Ltda. O arquivo apresentava 53.683, 45.136, 52.937 e 56.471 informações de C, P, M e GND, respectivamente. Os dados foram analisados pelo método da máxima verossimilhança restrita livre de derivadas, utilizando modelos animais. O modelo geral incluiu, como efeitos fixos, grupo de contemporâneos e as idades da vaca ao parto e do animal à desmama (efeitos linear e quadrático), heterozigose individual e os efeitos aleatórios genético aditivo direto, genético aditivo materno e de ambiente permanente materno. As herdabilidades diretas estimadas em análises univariadas foram 0,17, 0,15, 0,15 e 0,18, respectivamente, para C, P, M e GND. Os escores visuais, em análises bivariadas, mostraram-se positivamente associados entre si, com estimativas de correlações genéticas entre 0,92 e 0,96. Para GN

Genetic effects on preweaning weight gain of Nelore-Hereford calves according to different models and estimation methods.

Additive and nonadditive genetic effects on preweaning weight gain (PWG) of a commercial crossbred population were estimated using different genetic models and estimation methods. The data set consisted of 103,445 records on purebred and crossbred Nelore-Hereford calves raised under pasture conditions on farms located in south, southeast, and middle west Brazilian regions. In addition to breed additive and dominance effects, the models including different epistasis covariables were tested. Models considering joint additive and environment (latitude) by genetic effects interactions were also applied. In a first step, analyses were carried out under animal models. In a second step, preadjusted records were analyzed using ordinary least squares (OLS) and ridge regression (RR). The results reinforced evidence that breed additive and dominance effects are not sufficient to explain the observed variability in preweaning traits of Bos taurus x Bos indicus calves, and that genotype x environment interaction plays an important role in the evaluation of crossbred calves. Data were ill-conditioned to estimate the effects of genotype x environment interactions. Models including these effects presented multicolinearity problems. In this case, RR seemed to be a powerful tool for obtaining more plausible and stable estimates. Estimated prediction error variances and variance inflation factors were drastically reduced, and many effects that were not significant under ordinary least squares became significant under RR. Predictions of PWG based on RR estimates were more acceptable from a biological perspective. In temperate and subtropical regions, calves with intermediate genetic compositions (close to 1/2 Nelore) exhibited greater predicted PWG. In the tropics, predicted PWG increased linearly as genotype got closer to Nelore.