Data on 23925 lactations of 5897 Sahiwal cows in five Government herds of Punjab (Pakistan) viz. Livestock Experiment Station Allahdad, Bahadurnagar, Fazalpur, Jahangirabad and Khizerabad (1964-2004) were collected to document the behavior of various productive and reproductive traits of Sahiwal cows with respect to herd, year and season of calving and parity. A linear model was used to determine the effects of various environmental factors on performance traits. The 305-day milk yield, total milk yield, lactation length, dry period, calving interval and service period averaged 1530.5±12.36 kg, 1552.1±12.15 kg, 235±1.4 days, 218±2.1 days, 438±2.7 days and 151±2.8 days, respectively. All the productive and reproductive traits were affected (p<0.01) by herd, year, season of calving and parity. Lactation length was important covariable for yield traits while yield was important for dry period, service period and calving interval. Maximum yield was recorded for 5^th parity cows. Calving interval differed by two months among herds. Cows calving in most frequent calving season (winter) produced more milk than summer calvers (1608.6±12.91 kg vs 1474.1±13.63 kg). The phenotypic trends for 305-day milk yield, total milk yield, lactation length, dry period, calving interval and service period were -1.33 kg, -0.21 kg, -1.27 days, +1.52 days, +0.32 days and +0.59 days, respectively. Lactation length (244.5 days) was used as covariable. Improvement in feeding and breeding management and culling on productivity may improve the performance of Sahiwal cows.

Key words: Cattle, Environmental factors, Performance traits, Phenotypic trend, Sahiwal