Research Institute for Physiology of Animal Reproduction, Bhunikey (Pattoki), Distt. Kasur, Pakistan-55300. 

    Productive and reproductive performance parameters of Holstein-Friesian cows kept at the Livestock Experiment Station, Bhunikey (Pattoki), District Kasur for the period from 1991 to 2000 were studied. The average values for age at maturity, age at first conception and age at first calving were 652.70 ± 6.98, 714.74 ± 9.72 and 987.87 ± 9.81 days, respectively and the differences of these parameters during different seasons of birth were statistically non-significant. The average calving to first insemination interval, service period and calving interval in these cows were 113.34 ± 3.45, 222.22 ± 6.87 and 505.02 ± 8.28 days, respectively. Effect of parity on these parameters was statistically non-significant. On the other hand, the effect of calving season on calving to first insemination interval, service period and calving interval was statistically significant (P<0.05). The cows calving during humid hot season showed significantly (P<0.05) lower calving to first insemination and calving interval as compared to those calving during winter and spring seasons. The cows calving during autumn and humid hot seasons showed significantly (P<0.05) lower service period as compared to those calving during winter and spring seasons. The average number of services per conception was 3.07 ± 0.10. The differences of the number of services per conception during 6^th lactation with those of 1^st and 8^th lactation were statistically significant (P<0.05). The average gestation period was 278.61 ± 0.29 days. Higher gestation period was observed in cows carrying male calves than cows carrying female calves and this difference was statistically non-significant. The average lactation length and dry period were 291.86 ± 6.55 and 224.99 ± 10.00 days, respectively, while the average lactation milk yield was 2772.76 ± 65.00 liters. The differences of lactation milk yield between 7^th and 3^rd lactation were statistically significant (P<0.05). Similarly, the lactation milk yield during 6^th lactation was significantly (P<0.05) lower from those of 3^rd, 4^th and 5^th lactations. The frequencies of calving during winter, spring, dry hot, humid hot and autumn seasons were 17.73, 16.35, 7.92, 35.45 and 22.55%, respectively.