Technical note: A general transformation formula for interval traits connected with reproduction in pigs.

A general transformation formula is presented for interval traits in pigs, such as weaning-to-first-service interval or farrowing interval. In the logarithmic transformation, only observations that are greater than the median of the trait as originally recorded are transformed. The transformation considerably reduces the skewness and kurtosis of the trait so that the distribution of transformed data approaches normality. In analysis of >12,000 records for weaning-to-first-service interval and >9,000 records for farrowing interval, heritability estimates for the transformed data were greater than for the data as recorded. Therefore, selection on the transformed trait should be more effective than selection on the original trait. The transformation formula is likely to be appropriate for other livestock species and traits.