The value of recording body measurements in beef cattle

[摘要] English: Body size and shape are objectively described using body measurements in beef cattle. Howthese measures of size and shape relate to the functioning of the individual is of paramountimportance to livestock producers. Changes in these parameters that lead to inefficientanimals are never welcomed by farmers. Therefore, constant checks on the relationshipsbetween body measurements and performance traits are vital in selection programs.To estimate heritabilities and genetic correlations among body measurements andgrowth traits, data of 7 266 performance records of Bonsmara bull calves participatingin on-farm growth tests (Phase D) were used. The data set was extracted from the IntegratedRegistration and Genetic Information System (INTERGIS) of South Africa. Thedata covered a 25-year period i.e. from 1972 - 1996. Data were recorded from 45 herds,with 439 sires and 5 180 dams involved. Traits analyzed were scrotal circumference (SC),body length (BL), shoulder height (SH), birth weight (BW), weaning weight (WW), finalweight (FW) and average daily gain (ADG) from weaning to final test date.Multivariate REML methodology was used to estimate (co)variances and genetic componentsfor different traits. In cases where there were more than one value for an estimate,the values were pooled, weighting each estimate by the inverse of its sampling variance.Different models were, however, fitted for each trait. The permanent environmental effectwas found to be important for most of the post-weaning traits, but it could, however, notbe considered in the multivariate runs. This was due to computational limitations imposedby the data set. A simple model considering only direct animal effect and random errorwas fitted for all post-weaning traits.Heritability estimates for body measurements ranged from medium for body length(0.27±0.05) to high for shoulder height (0.42±0.05) and scrotal circumference (0.46±0.06).Corresponding estimates for performance traits were: direct (0.31±0.05) and maternalbirth weight (0.10±0.03), direct (0.29±0.05) and maternal weaning weight (0.04±0.02),average daily gain (0.19±0.04) and final weight (0.30±0.05).Generally, body measurements were favourably and positively correlated with performancetraits (0.03 to 0.83). However, scrotal circumference was found to be geneticallyweakly correlated to maternal birth weight (-0.22±0.15) and average daily gain(0.1O±O.13). A close to zero genetic correlation was found between average daily gain andmaternal weaning weight (0.03±0.17). These results suggest that selection for fast growingbulls may not influence maternal performance at weaning.Considering the favourable genetic correlations between body measurements and performancetraits, it could be inferred that selection for body measurements is compatiblewith that of performance traits. However, a further study should be conducted to evaluatewhich of those traits considered in this study are of economic importance so that anappropriate selection index can be developed.

[发布机构] University of the Free State