A total of 255,538 performance records in competitions with Spanish Trotter Horses, collected from 1991 to 2007, were used to include and evaluate competitive information using the Thurstonian model. The model analysis included: sex (2 classes), age (3) and race (3920) as systematic effects; and trainer-driver, permanent environment and genetic effects as random effects. The pedigree file included 10,940 animals. REML methodology was also used to compare the results obtained with the same and similar traits. The heritability obtained was 0.09, which is within the range of the values reported in the reviewed literature for ranking traits in horses, and similar to the value obtained for the same trait with the same model and the same database using a REML methodology (0.05). The trainer-driver effect had a total variability of 17%, similar to the effect of the rider in other equestrian disciplines. Males were 0.15 better than females in standard deviations, and young animals were 0.24 better than middle-aged animals and 0.59 better than the older animals in standard deviations. The differences in the animals' genetic ranking by their breeding values are also shown using the percentage of coincidence for the top and bottom 20% of the animals in the genetic ranking, and elite horses (top 5%). Higher values were obtained in the comparison with the same trait, the same model and the same database using REML methodology (ranging between 89.39% and 92.81% for the top 5% and bottom 20%, respectively). The practical application of this model has therefore shown adequate results. It allows us to compare between the underlying variable without the effect of race level, and produces more suitable estimations for genetic parameters and breeding values in the population. The inclusion of the race effect in the model is also important, because with a mixed animal model approach, the information for breeding values and permanent environmental effect comes from several races with sufficient genetic connectedness, although competitions are usually structured into categories according to the technical level of difficulty linked to the technical ability of the horses' performance. © 2011 Elsevier B.V.
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