The connectedness of environmental factors herd-year-seasons (HYS) was examined in datasets used in routine genetic evaluation of Czech Large White and Czech Landrace breed. The Genetic Drift Variance method suggested by Kennedy and Trus (1993) was used. The highest connectedness of HYS was found in reproduction data of second and later litters (0,292 and 0,348), lower values of connectedness (0,556 and 0,585) was reached in production data and the lowest connectedness (0,598 and 0,662) was found in datasets of the first litters. About 80% of the evaluated herds had more than 50% HYS connected with used minimal criterion of 75% quantile. Over the analysed period no negative trend in connectedness has been discovered.