Breeding for crossbred performance
Traditionally, estimation of breeding values has used data collected from purebred animals collected at nucleus farms. Although this strategy has enabled important genetic progress for decades, improvements made at the nucleus are not fully realized at the commercial level. This inefficiency is expected in traits for which the genetic correlation between purebred and crossbred performance deviates considerably from one, a characteristic that is typical for production traits, such as feed intake and growth.
There are different reasons for a low genetic correlation between purebred and crossbred performance: the presence of dominance, imprinting, and genetic differences between breeds. Moreover, specific genotypes can show different effects in different environments (genotype by environment (GxE) effects). Therefore, dominance, imprinting and breed-specific effects could be considered in order to improve the efficiency of selection when selecting purebreds for crossbred performance. Furthermore, crossbred field data could be included, in addition to purebred data, in the genetic evaluations to account for GxE effects.
Crossbreds in the genomics era
With the implementation of genomic selection in pig breeding, the genetic progress in purebred populations is expected to increase by more than 35% compared to traditional selection. However, as most animals in the pork production system are crossbreds, the increase in genetic progress in purebreds will add much more value to commercial production if this progress is also realized in crossbreds.
The genome of crossbred animals is formed by the combination of alleles inherited from the parental breeds that may be expressed differently according to their parental or breed of origin, but also depending on the interaction between alleles and the environment where the animals are located. Topigs Norsvin has focused on a better understanding of such combination and interaction of alleles to maximize the accuracy of selection in purebreds for crossbred performance.
To strengthen genetic progress in crossbred populations, Topigs Norsvin now includes genotypes and phenotypes of commercial crossbred animals into the genetic evaluation. Many projects at Topigs Norsvin have been carried out in order to investigate the best models and strategies to include crossbred genomic data into the genetic evaluation, including:
PhD project of Renata Veroneze
Renata evaluated how linkage disequilibrium (LD) can affect genomic selection. She showed that the LD patterns in purebred lines are not the same. This is an indicator that using crossbred data in the genetic evaluations of crossbred performance will result in higher prediction accuracies compared to using purebred data only.
PhD project of André Hidalgo
The main goal of André’s thesis was to exploit genomic information from purebred and crossbred pigs. He showed that selecting purebreds for crossbred performance was more accurate when crossbred data were used in the genetic evaluations compared to using purebred data.
PhD project of Marcos Lopes
Marcos’ PhD thesis evaluated and further developed different models of genomic information to improve selection of
purebreds for crossbred performance. The results presented in his thesis show that by going beyond traditional genomic selection models, performance of animals can be predicted more accurately.