Scrotal circumference data from 47,605 Nellore young bulls, measured at around 18 mo of age (SC18), were analyzed simultaneously with 27,924 heifer pregnancy (HP) and 80,831 stayability (STAY) records to estimate their additive genetic relationships. Additionally, the possibility that economically relevant traits measured directly in females could replace SC18 as a selection criterion was verified. Heifer pregnancy was defined as the observation that a heifer conceived and remained pregnant, which was assessed by rectal palpation at 60 d. Females were exposed to sires for the first time at about 14 mo of age (between 11 and 16 mo). Stayability was defined as whether or not a cow calved every year up to 5 yr of age, when the opportunity to breed was provided. A Bayesian linear-threshold-threshold analysis via Gibbs sampler was used to estimate the variance and covariance components of the multitrait model. Heritability estimates were 0.42 ± 0.01, 0.53 ± 0.03, and 0.10 ± 0.01, for SC18, HP, and STAY, respectively. The genetic correlation estimates were 0.29 ± 0.05, 0.19 ± 0.05, and 0.64 ± 0.07 between SC18 and HP, SC18 and STAY, and HP and STAY, respectively. The residual correlation estimate between HP and STAY was -0.08 ± 0.03. The heritability values indicate the existence of considerable genetic variance for SC18 and HP traits. However, genetic correlations between SC18 and the female reproductive traits analyzed in the present study can only be considered moderate. The small residual correlation between HP and STAY suggests that environmental effects common to both traits are not major. The large heritability estimate for HP and the high genetic correlation between HP and STAY obtained in the present study confirm that EPD for HP can be used to select bulls for the production of precocious, fertile, and long-lived daughters. Moreover, SC18 could be incorporated in multitrait analysis to improve the prediction accuracy for HP genetic merit of young bulls.

RESUMO -Registros de 24.703 animais da raça Nelore, provenientes de seis fazendas, foram utilizados para estimar os coeficientes de herdabilidade e a correlação genética relativos às características probabilidade de prenhez aos 14 meses (PP14) e altura na garupa aos 450 dias de idade (AG450). O modelo matemático incluiu os efeitos fixos de grupo de contemporâneo (181 grupos) e classe de idade da mãe ao parto (7 classes) para PP14 e o efeito fixo de grupo de contemporâneo (584 grupos) para AG450. Os efeitos aleatórios incluídos em ambos os modelos foram genético aditivo do touro e residual. Os componentes de variância e covariância foram obtidos pelo método ℜ. As estimativas de herdabilidade foram iguais a 0,73 ± 0,01 e 0,30 ± 0,00 para PP14 e AG450, respectivamente. A estimativa da correlação genética entre as características foi 0,10 ± 0,01. Os resultados mostram que PP14 pode ser usada em programas de seleção de touros com o intuito de aumentar a precocidade das novilhas, dado o alto valor de herdabilidade estimado para esta característica. A baixa correlação genética entre PP14 e AG450 sugere que seleção para crescimento, medida na altura da garupa, pouco poderá afetar a precocidade das novilhas medida pela PP14.Palavras-chave: altura na garupa, correlação genética, herdabilidade, método ℜ, prenhez de novilha Estimation of Genetic Parameters for Probability of Pregnancy at 14 Months and HipHeight in Nelore Beef Cattle ABSTRACT -Records of 24,703 Nelore cattle from six herds were used to estimate coefficients of heritability for probability of pregnancy at 14 months (PP14) and hip height (HH) traits. For PP14, the mathematical model included as fixed effects the contemporary groups (181 groups) and dam age class at calving (7 classes) and for HH only contemporary groups (584 groups). Random effects included were genetic additive of sire and residual effects. Variance and covariance components were obtained by method ℜ. Heritability estimates were 0.73 ± 0.01 and 0.30 ± 0.00 for PP14 and HH, respectively. Genetic correlation estimate between PP14 and HH was 0.10 ± 0.01. Results reveal that PP14 is of high heritability and, therefore, it can be indicated for selection programs of bulls with the objective of increasing the heifer fertility. The value of the genetic correlation suggests low genetic correlation between the two traits, indicating that selection for growth, measured by the HH, is not a so strong antagonism to the precocity of the heifers measured by PP14.Key Words: genetic correlation, heritability, hip height, method ℜ, probability of pregnancy at 14 months R. Bras. Zootec., v.32, n. IntroduçãoAs avaliações genéticas com a disponibilização da diferença esperada na progênie (DEP) têm sido uma ferramenta fundamental para a obtenção de progresso genético nos rebanhos de corte. As características relacionadas ao crescimento têm sido as mais trabalhadas e acredita-se que em pouco tempo um ponto ótimo para as diversas regiões de criação deverá ser atingido nos rebanhos para estas características. No enta...

The objectives of the current study were to assess the feasibility of using stayability traits to improve fertility of Nellore cows and to examine the genetic relationship among the stayabilities at different ages. Stayability was defined as whether a cow calved every year up to the age of 5 (Stay5), 6 (Stay6), or 7 (Stay7) yr of age or more, given that she was provided the opportunity to breed. Data were analyzed based on a maximum a posteriori probit threshold model to predict breeding values on the liability scale, whereas the Gibbs sampler was used to estimate variance components. The EBV were obtained using all animals included in the pedigree or bulls with at least 10 daughters with stayability observations, and average genetic trends were obtained in the liability and transformed to the probability scale. Additional analyses were performed to study the genetic relationship among stayability traits, which were compared by contrasting results in terms of EBV and the average genetic superiority as a function of the selected proportion of sires. Heritability estimates and SD were 0.25 +/- 0.02, 0.22 +/- 0.03, and 0.28 +/- 0.03 for Stay5, Stay6, and Stay7, respectively. Average genetic trends, by year, were 0.51, 0.34, and 0.38% for Stay5, Stay6, and Stay7, respectively. Estimates of EBV SD, in the probability scale, for all animals included in the pedigree and for bulls with at least 10 daughters with stayability observations were 7.98 and 12.95, 6.93 and 11.38, and 8.24 and 14.30% for Stay5, Stay6, and Stay7, respectively. A reduction in the average genetic superiorities in Stay7 would be expected if the selection were based on Stay5 or Stay6. Nonetheless, the reduction in EPD, depending on selection intensity, is on average 0.74 and 1.55%, respectively. Regressions of the sires' EBV for Stay5 and Stay6 on the sires' EBV for Stay7 confirmed these results. The heritability and genetic trend estimates for all stayability traits indicate that it is possible to improve fertility with selection based on a threshold analysis of stayability. The SD of EBV for stayability traits show that there is adequate genetic variability among animals to justify inclusion of stayability as a selection criterion. The potential linear relationship among stayability traits indicates that selection for improved female traits would be more effective by having predictions on the Stay5 trait.

ABSTRACT. Survival or longevity is an economically important trait in beef cattle. The main inconvenience for its inclusion in selection criteria is delayed recording of phenotypic data and the high computational demand for including survival in proportional hazard models. Thus, identification of a longevity-correlated trait that could be recorded early in life would be very useful for selection purposes. We estimated the genetic relationship of survival with productive and reproductive traits in Nellore cattle, including weaning weight (WW), post-weaning growth (PWG), muscularity (MUSC), scrotal circumference at 18 177 ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 9 (1): 176-187 (2010) Genetic relationship of longevity with fertility traits in Nellore cattle months (SC18), and heifer pregnancy (HP). Survival was measured in discrete time intervals and modeled through a sequential threshold model. Five independent bivariate Bayesian analyses were performed, accounting for cow survival and the five productive and reproductive traits. Posterior mean estimates for heritability (standard deviation in parentheses) were 0.55 (0.01) for WW, 0.25 (0.01) for PWG, 0.23 (0.01) for MUSC, and 0.48 (0.01) for SC18. The posterior mean estimates (95% confidence interval in parentheses) for the genetic correlation with survival were 0. 16 (0.13-0.19), 0.30 (0.25-0.34), 0.31 (0.25-0.36), 0.07 (0.02-0.12), and 0.82 (0.78-0.86) for WW, PWG, MUSC, SC18, and HP, respectively. Based on the high genetic correlation and heritability (0.54) posterior mean estimates for HP, the expected progeny difference for HP can be used to select bulls for longevity, as well as for post-weaning gain and muscle score.

RESUMO -Com o objetivo de comparar as estimativas de parâmetros genéticos obtidas pelos métodos de máxima verossimilhança restrita (REML) e ℜ, foram realizadas análises uni-características sob modelo animal, para os quais foi utilizado um conjunto de dados da raça Nelore. Os modelos estatísticos incluíram os efeitos fixos de grupo de contemporâneos (fazenda, ano de nascimento, sexo e grupos de manejo à desmama e ao sobreano) e idade do animal (covariável linear), e como aleatórios foram considerados os efeitos genético aditivo direto e residual. As estimativas dos coeficientes de herdabilidade foram 0,36 e 0,39 para peso aos 18 meses (PESSOB); 0,27 e 0,29 para ganho de peso da desmama aos 18 meses (GP345); 0,22 e 0,21 para conformação (CONF); 0,21 e 0,21 para precocidade de acabamento (PREC); e 0,22 e 0,22 para musculosidade (MUSC), respectivamente, pelo REML e método ℜ. Em todas as estimativas de herdabilidade, o erro-padrão foi menor ou igual a 0,02. As diferenças entre as estimativas de tendência genética obtidas pelos dois métodos foram pequenas e as correlações de Spearman entre os valores genéticos preditos usando os componentes de variância obtidos por ambos os métodos foram iguais a 1 para todas as características analisadas. Os resultados sugerem que os métodos REML e ℜ fornecem os mesmos resultados e que o método ℜ pode ser utilizado como uma opção ao REML em análises uni-características, principalmente pela menor demanda computacional.Palavras-chave: características de crescimento, escore visual, Método ℜ, Nelore, parâmetros genéticos, REML Estimate of Genetic Parameters in Beef Cattle Using Restricted Maximun Likelihood and Method ℜABSTRACT -The objective of this paper was to compare the estimates of genetic parameters obtained by REML and method ℜ. Animal model single-trait analyses were performed using a data set of Nellore cattle. Statistical models included fixed effects of contemporary group (herd, year, sex and management groups at weaning and 550 days) and age of animal (covariable-linear effect), and additive genetic and residual random effects. Heritability estimates were 0.36 and 0.39 for weight at 550 days (W550); 0.27 and 0.29 for weight gain from weaning to 550 days (WG345); 0.22 and 0.21 for conformation (CONF); 0.21 and 0.21 for precocity (PREC) and 0.22 and 0.22 for muscling (MUSC), respectively, by REML and method ℜ. For all heritability estimates, standard errors were lower than or equal to 0.02. The differences in the estimates of genetic trend obtained from the two methods were low for all traits. Spearman rank correlation between breeding values obtained in the analyses using the variance components obtained by REML and method ℜ were equal to 1 for all traits. The results suggest that REML and method ℜ provide similar results and that method ℜ can be used as an alternative to REML in single-trait analyses, mainly due to lower computational requirements. IntroduçãoOs componentes de variância, importantes na predição do mérito genético dos indivíduos, têm sido estimados por difere...