RESUMO -Visando estimar parâmetros genéticos em bovinos, foram utilizados registros de pesos padronizados aos 120, 210, 365, 450 e 550 dias de idade (P120, P210, P365, P450 e P550), altura do posterior mensurada próxima ao sobreano (ALT) e circunferências escrotais (CE) padronizadas aos 365, 450 e 550 dias de idade (CE365, CE450 e CE550). Os dados foram provenientes de animais machos e fêmeas, nascidos entre 1998 e 2003 em dez fazendas de seis estados brasileiros. Os componentes de (co)variância foram estimados pela metodologia REML em análises uni, bi e trivariadas, utilizando-se 68, 0.64, 0.53, 0.58 and 0.59. Genetic correlations between W120 and SC adjusted for weight and age were close to zero, but positive and moderate when SC was adjusted only for age. Estimates of genetic correlation between HH and SC adjusted for weight and age were -0.19 (SC365), -0.24 (SC450) and 0.00 (SC550). The same parameter estimates when SC was adjusted only for age were 0.21 (SC365), 0.12 (SC450) and 0.39 (SC550). These results indicate genetic variability for growth traits and SC. Selection for weight at any age will increase stature. In order to obtain Nelore cattle with stature and weight suitable to the production system, both traits should be included in a selection index.

The aim of the present study was to evaluate the genetic correlations among real-time ultrasound carcass, BW, and scrotal circumference (SC) traits in Nelore cattle. Carcass traits, measured by real-time ultrasound of the live animal, were recorded from 2002 to 2004 on 10 farms across 6 Brazilian states on 2,590 males and females ranging in age from 450 to 599 d. Ultrasound records of LM area (LMA) and backfat thickness (BF) were obtained from cross-sectional images between the 12th and 13th ribs, and rump fat thickness (RF) was measured between the hook and pin bones over the junction between gluteus medius and biceps femoris muscles. Also, BW (n = 22,778) and SC (n = 5,695) were recorded on animals born between 1998 and 2003. The BW traits were 120, 210, 365, 450, and 550-d standardized BW (W120, W210, W365, W450, and W550), plus BW (WS) and hip height (HH) on the ultrasound scanning date. The SC traits were 365-, 450-, and 550-d standardized SC (SC365, SC450, and SC550). For the BW and SC traits, the database used was from the Nelore Breeding Program-Nelore Brazil. The genetic parameters were estimated with multivariate animal models and REML. Estimated genetic correlations between LMA and other traits were 0.06 (BF), -0.04 (RF), 0.05 (HH), 0.58 (WS), 0.53 (W120), 0.62 (W210), 0.67 (W365), 0.64 (W450 and W550), 0.28 (SC365), 0.24 (SC450), and 0.00 (SC550). Estimated genetic correlations between BF and with other traits were 0.74 (RF), -0.32 (HH), 0.19 (WS), -0.03 (W120), -0.10 (W210), 0.04 (W365), 0.01 (W450), 0.06 (W550), 0.17 (SC365 and SC450), and -0.19 (SC550). Estimated genetic correlations between RF and other traits were -0.41 (HH), -0.09 (WS), -0.13 (W120), -0.09 (W210), -0.01 (W365), 0.02 (W450), 0.03 (W550), 0.05 (SC365), 0.11 (SC450), and -0.18 (SC550). These estimates indicate that selection for carcass traits measured by real-time ultrasound should not cause antagonism in the genetic improvement of SC and BW traits. Also, selection to increase HH might decrease subcutaneous fat as correlated response. Therefore, to obtain animals suited to specific tropical production systems, carcass, BW, and SC traits should be considered in selection programs.

No abstract

One of the main animal health problems in tropical and subtropical cattle production is the bovine tick, which causes decreased performance, hide devaluation, increased production costs with acaricide treatments, and transmission of infectious diseases. This study investigated the utility of genomic prediction as a tool to select Braford (BO) and Hereford (HH) cattle resistant to ticks. The accuracy and bias of different methods for direct and blended genomic prediction was assessed using 10,673 tick counts obtained from 3,435 BO and 928 HH cattle belonging to the Delta G Connection breeding program. A subset of 2,803 BO and 652 HH samples were genotyped and 41,045 markers remained after quality control. Log transformed records were adjusted by a pedigree repeatability model to estimate variance components, genetic parameters, and breeding values (EBV) and subsequently used to obtain deregressed EBV. Estimated heritability and repeatability for tick counts were 0.19 ± 0.03 and 0.29 ± 0.01, respectively. Data were split into 5 subsets using k-means and random clustering for cross-validation of genomic predictions. Depending on the method, direct genomic value (DGV) prediction accuracies ranged from 0.35 with Bayes least absolute shrinkage and selection operator (LASSO) to 0.39 with BayesB for k-means clustering and between 0.42 with BayesLASSO and 0.45 with BayesC for random clustering. All genomic methods were superior to pedigree BLUP (PBLUP) accuracies of 0.26 for k-means and 0.29 for random groups, with highest accuracy gains obtained with BayesB (39%) for k-means and BayesC (55%) for random groups. Blending of historical phenotypic and pedigree information by different methods further increased DGV accuracies by values between 0.03 and 0.05 for direct prediction methods. However, highest accuracy was observed with single-step genomic BLUP with values of 0.48 for -means and 0.56, which represent, respectively, 84 and 93% improvement over PBLUP. Observed random clustering cross-validation breed-specific accuracies ranged between 0.29 and 0.36 for HH and between 0.55 and 0.61 for BO, depending on the blending method. These moderately high values for BO demonstrate that genomic predictions could be used as a practical tool to improve genetic resistance to ticks and in the development of resistant lines of this breed. For HH, accuracies are still in the low to moderate side and this breed training population needs to be increased before genomic selection could be reliably applied to improve tick resistance.

Resumo -O objetivo deste trabalho foi estimar correlações genéticas e fenotípicas entre escores visuais e características de carcaça medidas por ultrassom, para verifi car a efi cácia desses escores na determinação da musculosidade e na avaliação da carcaça. As características de carcaça medidas por ultrassom foram área de olho de lombo (AOL) e espessura de gordura subcutânea (EG), mensuradas entre a região da 12 a e 13 a costelas, bem como a espessura de gordura subcutânea na garupa (EGP8). As características de estrutura (E), precocidade (P) e musculosidade (M) foram avaliadas por meio de escores visuais. Os componentes de covariância usados para estimar as correlações genéticas e fenotípicas foram obtidos pelo método da máxima verossimilhança restrita, em uma análise multicaracterística. As estimativas de correlações genéticas entre AOL e E, P e M foram 0,54, 0,58 e 0,61, respectivamente, e indicaram que, a longo prazo, a utilização da AOL como critério de seleção poderá produzir animais com maiores escores visuais para essas características. As correlações genéticas estimadas entre as espessuras de gordura (EG e EGP8) e os escores P e M apresentaram comportamento semelhante. Entretanto, as correlações genéticas entre as espessuras de gordura (EG e EGP8) e E foram próximas de zero. As correlações fenotípicas seguiram as mesmas tendências das respectivas correlações genéticas. Essas estimativas indicam que os escores visuais são determinados, em parte, pelos mesmos conjuntos de genes que infl uenciam a AOL.Termos para indexação: componente de variância, correlação fenotípica, herdabilidade, musculosidade, parâmetro genético. Genetic correlations between visual scores and carcass traits measured by real-time ultrasound in beef cattleAbstract -The aim of this work was to evaluate the genetic and phenotypic correlations between carcass traits measured by real-time ultrasound and by visual scores, in order to verify the effectiveness of these scores in determining muscularity and carcass fat. Carcass traits measured by real-time ultrasound were longissimus muscle area (LMA) and backfat thickness (BF), obtained between the 12 th and 13 th ribs, as well as the rump fat thickness (RF). The visual scores for the traits of body structure (E), precocity (P), and muscle (M) were evaluated individually. The genetic and phenotypic parameters were estimated by multivariate analysis, using restricted maximum likelihood methodology. The estimated genetic correlations between LMA and E, P and M were 0.54, 0.58 and 0.61, respectively, indicating that, in the long term, the use of LMA as a selection criterion might produce animals with higher visual scores. Similar genetic correlations were found between both subcutaneous fat measures (BF and RF) and P and M scores. However, genetic correlations between both subcutaneous fat measures and E were close to zero. The phenotypic correlations followed the same trends of their respective genetic correlations. These estimates indicate that the visual scores and LMA are, in part, determi...

RESUMO -Foram avaliados 27.523 e 21.746 registros das características conformação, precocidade e musculatura à desmana e ao sobreano, respectivamente, para estimar os componentes de covariância entre estas características e entre estas e os pesos corporais medidos nas mesmas idades. Para as análises dos dados, foram empregados modelos animais com efeitos genéticos direto e materno e efeito de ambiente permanente materno. Máxima verossimilhança restrita foi empregada para estimar os parâmetros genéticos. As estimativas de herdabilidade dos escores à desmama foram 0,13; 0,25 e 0,23 para conformação, precocidade e musculatura, respectivamente. As estimativas de herdabilidade dos escores visuais avaliados ao sobreano foram de maiores magnitudes (0,24; 0,32 e 0,27 para conformação, precocidade e musculatura, respectivamente).As estimativas das correlações genéticas entre escores medidos às mesmas idades, considerando desmana e sobreano, foram 0,67 e 0,75 entre conformação e precocidade; 0,61 e 0,71 entre conformação e musculatura; 0,95 e 0,95 entre precocidade e musculatura. As correlações genéticas estimadas entre o peso corporal à desmama e conformação, precocidade e musculatura, respectivamente, foram 0,97; 0,67 e 0, 62. As estimativas entre conformação, precocidade, musculatura ao sobreano e o peso corporal foram 0,83; 0,59 e 0,58, respectivamente. Os resultados indicam que os escores visuais podem ser utilizados como critérios de seleção. Aumento nos pesos corporais deve ser esperado como resposta correlacionada à seleção para essas características.Palavras-chave: avaliação visual, correlação genética, gado de corte, herdabilidade, Nelore, peso Genetic parameters estimates for visual scores and their association with body weight in beef cattleABSTRACT -It was evaluated 27,523 and 21,746 records on traits of conformation, finishing precocity and musculature measured at weaning and a year after weaning, respectively, for the estimation of (co)variance components among these traits, and between them and body weights at the same ages. The data were analyzed by employing an animal model with direct and maternal genetic effect and permanent maternal environment effect. Restricted maximum likelihood was employed for the estimation of genetic parameters. The heritability estimates of visual scores at weaning were 0.13, 0.25, 0.23 for conformation, finishing precocity, and musculature respectively. The heritability estimates of visual scores one year after weaning were greater: 0.24, 0.32 and 0.27 for conformation, finishing precocity, and musculature, respectively. The genetic correlations estimates among scores at the same ages were: 0.67 and 0.75 between conformation and finishing precocity; 0.61 and 0.71 between conformation and musculature; 0.95 and 0.95 between finishing precocity and musculature, considering weaning and one year further, respectively. The genetic correlations estimated between weaning weight and conformation, finishing precocity, and musculature, were 0.97, 0.67 and 0.62, respectively. The estimat...

Resumo -O objetivo deste trabalho foi determinar os fatores que afetam a altura da garupa em diferentes idades, em bovinos Nelore, e estimar a herdabilidade e as correlações genéticas entre esse caractere e as características reprodutivas e de crescimento. Os caracteres avaliados foram: altura da garupa à desmama, altura da garupa ao sobreano, peso à desmama, peso ao sobreano, perímetro escrotal e idade ao primeiro parto. Os fatores considerados foram: ano e mês de nascimento, rebanho, sexo, idade da vaca ao parto e idade do bezerro. Os componentes de variância e covariância foram estimados pela metodologia de máxima verossimilhança restrita, tendo-se utilizado um modelo animal. Todos os efeitos foram significativos para altura de garupa nas diferentes idades. As estimativas de herdabilidade quanto ao efeito genético direto indicaram que as características de crescimento e reprodutivas respondem à seleção, exceto a idade ao primeiro parto. As correlações genéticas entre as características de crescimento foram todas positivas e elevadas, de 0,42 a 0,90, o que indica que são determinadas em grande parte pelos mesmos conjuntos de genes de ação aditiva. Em razão das baixas magnitudes das estimativas de correlação genética (entre -0,14 e 0,16), a eficiência reprodutiva é pouco influenciada pela seleção quanto à altura de garupa.Termos para indexação: componentes de variância, correlações genéticas, herdabilidade, idade da vaca, idade do bezerro. Hip height and its relationships with reproductive and growth traits in Nelore cattleAbstract -The objective of this work was to determine factors that affect hip height at different ages, in Nelore cattle, and to estimate the heritability and the genetic correlation between this character and reproductive and growth traits. The analyzed traits were: hip height at weaning, hip height at post weaning, weight at weaning, weight at post weaning, scrotal circumference, and age at first calving. The analyzed factors were: year and month of birth, herd, sex, age of dam at calving, and calf age. The variance covariance components were estimate by the restrict maximum likelihood methodology using animal model. All effects were significant for hip height at different ages. The heritability estimates for direct genetic effects indicated that the growth and reproductive traits respond to selection, except for age at first calving. The genetic correlations between growth traits were positive and high, from 0.42 to 0.90, which indicates that they are mostly determined by the same group of genes with additive action. Due to the low magnitude of the estimated genetic correlations, from -0.14 to 0.16, the reproductive efficiency is little influenced by selection for hip height.

The objectives of the present study were to investigate the influence of yearling weight on the occurrence of early pregnancy and to determine differences between precocious and non-precocious heifers in terms of pre-and postnatal calf mortality, calf weight and height, mature cow weight, and stayability of the cow in the herd. Data from 26 977 females of a Nelore herd that participated in the breeding season between 1986 and 2004 were analyzed. The influence of yearling weight on sexual precocity and differences between precocious and non-precocious heifers in pre-and postnatal calf mortality and stayability were analyzed using the GENMOD procedure of the SAS program. Differences in the growth traits between precocious and non-precocious animals were estimated by contrast analysis. Three groups were analyzed for postnatal mortality: first calving of the heifers, calves born from the third calving and all offspring of the cow. In order to have a standardized calving to conception period for all females (precocious and non-precocious), calves born from the second calving were not included in the analysis. This was necessary because the first calving to conception period (days open) of precocious heifers was longer than for non-precocious due to farm reproductive management. No differences in postnatal mortality rates, from the third calving, were observed between the two groups of heifers studied. Analysis of all offspring of the dams showed a 9% higher probability of death of calves born to precocious heifers compared with calves born to non-precocious heifers. With respect to stayability, precocious heifers presented 33% greater odds to remain in the herd until 5 and 6 years of age and 28% greater odds to remain in the herd until 7 years when compared with non-precocious heifers. Precocious heifers weaned calves (205 days) significantly heavier than non-precocious ones, 1.410 and 0.797 kg considering the weaning weights of all offspring and of the third calving, respectively. With respect to sexual precocity, the results suggest that the probability of heifers to become pregnant at 16 months of age increases with increasing weight. However, heifers weighing more than 240 kg present practically the same pregnancy probability. Nevertheless, exposure of heifers during the early breeding season is recommended for beef cattle herds raised in tropical regions in view of the numerous benefits demonstrated here.