A. Sattar, R. H. Mirza and I. Ahmad

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

    Various parameters of reproductive efficiency of Jersey cows kept at the Livestock Experiment Station, Bhunikey (Pattoki), District Kasur, for the period from 1991 to 2000 were studied. The average values of age at maturity and age at first calving were 615.48 ± 8.23 and 926.48 ± 10.29 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 were 86.65 ± 1.71, 152.66 ± 4.85 and 430.15 ± 4.87 days, respectively. The differences of calving to first insemination interval among cows calved during different seasons were statistically non-significant. But the differences of calving to first insemination interval during 1^st lactation were significant (P<0.05) with those of 6^th, 7^th and 9^th lactations. Service period and calving interval in the Jersey cows calved during humid hot season were significantly (P<0.05) shorter as compared to those of cows calved during dry hot and spring seasons. Effect of parity on the service period was non-significant, but the effect of parity on the calving interval was significant (P<0.05), when the difference of calving interval during 7^th and 8^th lactation was compared. The average number of services per conception was 2.81 ± 0.09. The effect of parity on the number of services per conception was significant (P<0.05). The average gestation period was 277.63 ± 0.21 days. Higher gestation period was observed in cows carrying male calves than those carrying female calves (P<0.05). The frequency of calvings during winter, spring, dry hot, humid hot and autumn seasons was 19.32, 19.20, 9.79, 33.25 and 18.44 percent, respectively.

Key words: Reproductive efficiency, Jersey cows, Pakistan.