GENE-FLOW AND RELATIVE IMPORTANCE OF MATE RNAL, PATERNAL AND DIRECT EFFECTS IN DAIRY-CATTLE

The discounted gene-flow method was used to examine the relative impor tance of maternal effects compared to direct and paternal effects. Tra its considered are: calving-ease and proportion of still-born calves ( materna and direct effects) and non-return-rate (paternal and direct e ffects). Two types of weighting were compared: weighting according to the discounted sum of expressions (SDA) and weighting according to the long term limit of the number of realisations per year (AM). SDA were computed both with finite (10,15,20 and 25 years) and infinite planni ng horizon. Computations were done for five selection-paths: young bul ls, proven sires of bulls, proven sires of cows, dams of bulls and dam s of cows. Point zero on the time-scale was the birth of all calves fr om one year, a value of .95 was used as a discounting-factor. For all traits and selection-paths the ratio of SDA-values is heavily dependen t from the length of the planning-horizon (Tables 2 and 3, Figure 2). With infinite planning-term there is an unique limit for the traits re lated to calving, but not for non-return-rate (Tables 2 and 3, Figure 4). The number of realisations reach their long-term ratio of 1:1 (mat ernal:direct and maternal:paternal) after about 15 years (Figures 3,5 and 6). Because selection for functional traits needs a longterm strat egy, a unique ratio of 1:1 for all traits and selection-paths is recom mended.