Optimization of breeding schemes for sport horses
Introduction
Interest in horse sports and in horse breeding is on the increase. A relatively recent paper (Koenen et al., 2004) focused on breeding goals for sport horses, and this was followed by a review of the testing procedures used in different breeding schemes (Thorén Hellsten et al., 2006). Such breeding schemes share the same objectives but the procedure varies in different European countries. In France, for the last 20 years, selection has mainly focused on jumping horses, and is based on success in competition tests (Dubois and Ricard, 2007). The current objective of French breeders is to produce international jumping horses with increasing attention paid to functional traits such as conformation, gaits, riding temperament, locomotion problems and reproductive ability including aptitude for artificial insemination in males. New proposals have been made for the improvement of existing breeding schemes such as in-station selection tests for stallions. In some European countries, stallions are selected in special test stations after the measurement of performance (Bruns and Schade, 1998, Huizinga, 1990). These test stations enable the comparison of different stallions in the same environment but only a small number of candidates can be tested due to the cost of such structures. In Sweden special performance tests are used for the selection of stallions, with a week-long test that is repeated after an interval of 6-months, however, the Swedish test does not take place in a testing station. It shares the same characteristics with respect to genetic improvement, i.e. better heritability, but is limited to a small number of stallions (Gerber Olsson et al., 2000). The relevance of such breeding schemes has already been discussed in their own context: Ström and Philipsson (1978), Huizinga (1990), Philipsson et al. (1990), Koerhuis and van der Werf (1994), Bruns and Schade (1998), Gerber Olsson et al. (2000), Olsson (2006), Thorén Hellsten et al. (2006).
This study had three main objectives: 1. to model the standard breeding scheme currently used in France with new traits added to the breeding objectives, 2. to measure its characteristics and its efficiency, and 3. to compare it to an in-station test scheme.
Section snippets
Selection objective
The selection objective was a linear function of three traits. Competition jumping (CJ) was the main objective. The main secondary trait was conformation and gaits (CG). Other traits could be temperament, sperm quality or orthopaedic diseases. These traits are difficult and expensive to measure and require specific tests for temperament, sperm analysis for sperm quality, and X-Rays for developmental and orthopaedic diseases. We added a third trait (TT) to the selection objective, which could be
Genetic trend
The annual genetic trend of the standard breeding scheme was + 9.4% standard deviation units for the selection objective. Table 1 summarizes the genetic trends of the different breeding schemes. For CG, the genetic trend was + 2.6% standard deviation units, for CJ, the genetic trend was + 9.0% standard deviation units, and for TT, the genetic trend was + 1.5% standard deviation units. The male pathway contributed 74.2% of genetic progress.
Active stallions and broodmares
The replacement of the population required 333 active
Discussion
The limited sensitivity of the results to the parameters used in the model imply that our model results for the standard breeding scheme are sufficiently stable to make strategic decisions in breeding plans for jumping horses. Our main results were: 1. very atypical selection on progeny, 2. marked heterogeneity of selection among birth cohorts, 3. the need for an extensive field test or competition test whatever the breeding scheme of stallions (with or without an in-station test), 4. the
Conclusion
Four points are important in breeding schemes for sport horses. The first is that a progeny test is not essential (12% of progeny are issued from proven sires), except for rapid culling of stallions before their natural death (after 7 years of use). The second point is that selection of females should be taken into account as it can contribute 1/4 of genetic response. The third point is that extensive performance testing for competition jumping is necessary whatever the selection scheme for
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