Data on 871 calving and lactation records of Dutch Friesian cows in their second parity and above kept at the National Animal Research Centre, Naivasha were analyzed to investigate the effects of year and season of calving, parity, actual age at calving within parity and degree of calving ease 305 –a day (305 DMY) and lactation length (LL). The records were made over a period of 12 years, from 1971 to 1987. Effects of year season of birth, calving, parity and degree of calving ease were highly significant (p< 0.001). Of the two traits (p< 0.001). Age within parity was highly significant for 305-day milk yield only. An inverse relationship between type of calving and milk yield was observed, in which 305 day milk yield decreased substantially with increase in level of difficult calving.