Data on 58767 Austrian Fleckvieh lactation records representing 985 Al sires were used to estimate the change of genetic parameters of 100- and 305-day lactation milk traits with the advance of parity up to the fourth one. Milk traits were yields of milk, fat and protein an single traits and yield of fat-plus-protein and protein to fat ratio as composite traits. In most cases, sire of cow, cow-within-sire, year, season of calving, year X season interaction and both days open and age at calving (as linear and quadratic covarlates) had pronounced effects (P