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The purebred-crossbred correlation shows that crossbred information is important to optimize pig breeding programs
Production animals in pigs are generally crossbred animals, while selection takes place in purebred animals. That is why the genetic correlation between purebred and crossbred performance, known as the purebred-crossbred correlation, is very important. In a recently published review paper by researchers of Wageningen University & Research, the theory, estimates and implications of this purebred-crossbred correlation are discussed. This paper shows that the purebred-crossbred correlation likely differs from 1 for a lot of traits, indicating that crossbred information is very important to optimize breeding programs.
Theory
The purebred-crossbred correlation (rpc) is the genetic correlation between purebred and crossbred performance. When rpc is 1, purebred and crossbred performance are effectively the same trait. When rpc is lower than 1, it means that the best purebred animals don’t necessarily produce the best crossbred offspring. Therefore, it is more important to use crossbred information for selecting the best purebred animals when rpc is low. In this paper, it is shown theoretically that selecting purebred animals based on crossbred performance instead of purebred performance has a large impact on the genetic improvement in the purebred animals. Three different components underlie rpc, namely: 1) genotype by genotype interactions, since purebreds and crossbreds have different genetic backgrounds, 2) genotype by environment interactions, since purebreds and crossbreds are generally housed in different environments, and 3) differences in trait measurements.
Estimates and implications
In the invited review published in Journal of Animal Science, 201 rpc estimates in pigs from 27 studies were considered. The studies estimated the rpc for different purebred-crossbred combinations and a wide range of traits, that were divided in trait categories. The average rpc estimate was 0.63 which is considerably lower than 1, with 50% of the estimates between 0.45 and 0.87. For all different trait categories, e.g. Growth, Meat amount, Meat quality, Feed, and Fertility, the average rpc was around 0.6. This indicates that rpc is likely different from 1 and that for a lot of traits, crossbred information is very important to improve crossbred performance. Genotype by environment interactions appeared to have a smaller contribution to rpc than genotype by genotype interactions. More research regarding the impact of the different components on the rpc will help to improve breeding programs. Future studies are advised to carefully consider in which environment phenotypes are collected, to estimate separate rpc values for different pure lines, and to genotype the animals to improve the power to estimate rpc.