Abstract #764

# 764
Genetic selection for feed efficiency in crossbred animals.
Rob Bergsma*1, Egbert F. Knol1, 1Topigs Norsvin Research Centre B.V, Beuningen, the Netherlands.

Worldwide, the majority of the commercial slaughter pigs are a cross of 3 or even 4 purebred lines. Although genetic selection takes place in purebred lines, the breeding goal should be directed toward crossbred performance. Applying a crossbred breeding goal is important if purebred traits show a genetic correlation significantly lower than 1.0 with their crossbred counterparts and/or when the genetic variation of purebred traits is different from those of crossbred traits. Recent research showed that this especially applies to feed intake and feed efficiency, while carcass composition in purebreds and crossbreds appeared to be more similar traits. The percentage of the genetic trend in purebred lines, expressed in crossbreds can be calculated as the ratio of the crossbred genetic standard deviation multiplied by the genetic correlation and the genetic purebred standard deviation. Our results show that of the genetic progress in purebreds 62, 52, 111 and 85% is expressed in crossbreds for daily gain, feed intake, back fat and loin depth, respectively. For feed efficiency this ratio depends on the trait considered. For feed conversion ratio, 60% of the genetic trend in purebreds was expressed in crossbreds, whereas for residual feed intake this ratio was only 41%. Feed intake (and thus feed efficiency) are traits that are not widely available on individual crossbred animals. The limited availability may also indicate that the crossbred/purebred phenotypes are confounded with their environment, given rise to a possible genotype by environment interaction. Another possible explanation is that dominance plays a larger role in feed intake and feed efficiency compared with other traits. And finally, genomic selection has been implemented for purebreds but when using crossbred animals as reference population we have to take into account that a QTL in breed A can behave different than in breed B. Current research focuses on partitioning the possible causes in explaining the lower expression of the genetic trend of purebreds in crossbred. Results will facilitate decisions on the most appropriate genetic model to include crossbred information in a combined crossbred purebred breeding program.

Key Words: pig breeding, crossbred performance, feed efficiency