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Báo cáo sinh học: " Carcass conformation and fat cover scores in beef cattle: A comparison of threshold linear models vs grouped data models"

Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học quốc tế đề tài: Carcass conformation and fat cover scores in beef cattle: A comparison of threshold linear models vs grouped data models | Tarrés et al. Genetics Selection Evolution 2011 43 16 http www.gsejournal.Org content 43 1 16 Ge n et i cs Selection Evolution RESEARCH Open Access Carcass conformation and fat cover scores in beef cattle A comparison of threshold linear models vs grouped data models 1 1 2 1 Joaquim Tarrés Marta Fina Luis Varona and Jesus Piedrafita Abstract Background Beef carcass conformation and fat cover scores are measured by subjective grading performed by trained technicians. The discrete nature of these scores is taken into account in genetic evaluations using a threshold model which assumes an underlying continuous distribution called liability that can be modelled by different methods. Methods Five threshold models were compared in this study three threshold linear models one including slaughterhouse and sex effects along with other systematic effects with homogeneous thresholds and two extensions with heterogeneous thresholds that vary across slaughterhouses and across slaughterhouse and sex and a generalised linear model with reverse extreme value errors. For this last model the underlying variable followed a Weibull distribution and was both a log-linear model and a grouped data model. The fifth model was an extension of grouped data models with score-dependent effects in order to allow for heterogeneous thresholds that vary across slaughterhouse and sex. Goodness-of-fit of these models was tested using the bootstrap methodology. Field data included 2 539 carcasses of the Bruna dels Pirineus beef cattle breed. Results Differences in carcass conformation and fat cover scores among slaughterhouses could not be totally captured by a systematic slaughterhouse effect as fitted in the threshold linear model with homogeneous thresholds and different thresholds per slaughterhouse were estimated using a slaughterhouse-specific threshold model. This model fixed most of the deficiencies when stratification by slaughterhouse was done but it still failed to correctly fit .