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Evaluation models and genetic parameters for calving difficulty in beef cattle
1Institut National de la Recherche Agronomique, Station de Génétique Quantitative et Appliquée, 78 352 Jouy-en-Josas Cedex, France. phocas@dga.jouy.inra.fr
Journal of Animal Science
|May 2, 2003
Summary
Comparing statistical models for calving difficulty in beef cattle, a fixed linear model is best for practical breeding value prediction, especially with large herd-year groups. This model offers a reliable approach for genetic evaluations in Charolais cattle.
Area of Science:
- Animal Genetics
- Quantitative Genetics
- Livestock Breeding
Background:
- Calving difficulty is a significant trait in beef cattle breeding, impacting animal welfare and economic efficiency.
- Accurate prediction of breeding values for calving difficulty is crucial for genetic improvement programs.
- Various statistical models exist, but their suitability depends on data structure and herd management.
Purpose of the Study:
- To compare the performance of threshold and linear models for predicting breeding values for calving difficulty.
- To evaluate the impact of fixed versus random herd-year effects on model accuracy.
- To determine the most practical and accurate model for genetic evaluation in large Charolais herds.
Main Methods:
- Analysis of calving difficulty using threshold and linear models with fixed or random herd-year effects.
- Simulation of data sets with varying herd-year group sizes to assess model bias.
- Comparison of models using correlations of estimated breeding values (EBVs) from field data of 246,576 Charolais records.
Main Results:
- A linear model with a fixed herd-year effect was the most practical choice for predicting direct and maternal effects in large herds.
- While a threshold model with fixed herd-year effect is theoretically superior, the linear model provided high correlations (0.94 for direct, 0.98 for maternal EBVs) with the reference model.
- Heritabilities for direct and maternal effects and genetic correlations between them were estimated under different models.
Conclusions:
- The fixed linear model offers a practical and sufficiently accurate approach for predicting breeding values for calving difficulty in large Charolais populations.
- Model choice impacts the accuracy of genetic evaluations, highlighting the importance of considering herd-year group size.
- The findings support the use of the fixed linear model for routine genetic evaluations of calving difficulty in French Charolais cattle.