Abstract: Effect of year of calving, month, season and days in milk on daily milk yield of Holstein cattle at Cattle Breeding and Dairy Farm (CB&DF) Harichand, Pakistan was studied from 1990 through 1992. Association of various environmental stimuli with daily milk yield was also established. Year of calving, month, season and days in milk had a significant (P<0.01) effect on daily milk yield. Mean daily milk yield was higher (P<0.05) during 1991 (10.94?0.10 liters) and lower during 1992 (10.24?0.11 liters). Non significant differences were found in daily milk yield of cows during the year 1990 and 1992. Average daily milk yield was the highest (P<0.05) during January (12.50?0.23 liters), February (12.86?0.22 liters) and March (12.73?0.25 lieters) than during July (7.80?0.07 liters). Month had a significant (P<0.01) association with daily milk yield and a quadratic relationship was found between month of the year and daily milk yield. The adjusted R2 of the fitted model was 39.7%. Daily milk yield was nearly similar during winter (11.89?0.07 liters) and spring (11.72?0.16 liters) but on the average was higher (P<0.05) than that during summer (8.75?0.06 liters) and fall (9.70?0.13 liters). Daily milk yield was found significantly (P<0.01) associated days in milk (b=-0.026?0.001) and maximum ambient temperature (b=-0.01?0.004) with daily milk yield. The association of other environemntal stimuli like radiation, pan evaporation and rain fall with daily milk yield was not significant. Protection of lactating and pregnant cows from extreme climatic conditions, appropriate feeding and ample supply of green fodder will improve production performance of holstein cows at CB &Df, Harichand, NWFP, Pakistan.