4 withdrawal QTL in either the withdrawal selected lines or in the parental HS4 population; in contrast, we have reliably detected the Chr 9 QTL for consumption. Although, overall, the QTL data collected in this and previous studies appear generally discordant, this may well not be the case. For example, a QTL detected in one genotype may be silent in another, but the loci may have strong epistatic effects. To examine these and related issues, we are currently in the process of phenotyping a much larger HS4 population and densely genotyping these animals across the regions of interest.
