Micron blowout: heritability and genetic correlations with fibre diameter and secondary follicle diameter

Calculation of micron blowout as the difference between fibre diameter reco rds taken at different ages can produce 'biased' estimates of the heritabil ity and genetic correlations due to a scale effect. In some instances, stan dardisation of the fibre diameter records to a common genetic variance (i.e . removal of the scale effect) changed the heritability and the genetic cor relation estimates. The effect of standardisation on the heritability of mi cron blowout was determined to a large extent by the difference in the gene tic variance between the 2 fibre diameter measurements, whereas in the case of the genetic correlation between micron blowout and another trait, it wa s also dependent on the genetic correlation between the other trait and the two fibre diameters. It is recommended that heritabilities and genetic cor relations involving micron blowout be calculated after standardising the fi bre diameter measurements to a common genetic variance. The practical impli cations of the results are briefly discussed.