The genetic parameters of original and transformed farrowing interval were estimated in the presented study. The data of Czech Large White (CLW) and Czech Landrace (CLA) dam pig breed from January 1995 to December 2013 was provided by The Pig Breeders Association of the Czech Republic and were used for analyses. The transformation of farrowing interval was performed on the basis of the general transformation formula provided by Wolf (2012). The average original and transformed farrowing interval was 162 and 168 days for CLW and 165 and 161 for CLA, respectively. The estimated heritabilities of original farrowing interval were very low 0.048 and 0.045 for CLW and CLA, respectively. Proportions of residual variance of original farrowing interval data were high and similar for both breeds. Estimated heritabilities of transformed farrowing interval were 0.085 and 0.079 for CLW and CLA sows, respectively. The increase of heritability caused by transformation of original farrowing interval data sets was 77% and 76% for CLW and CLA, respectively. Proportions of variance for permanent sow effect were very low and the transformation of farrowing interval has negligible impact on it. A new transformation formula decrease variance, skewness and kurtosis of original farrowing interval distribution.