Analysis of Jersey crossbred cows for lactation specific demographic parameters

In present study, lactation specific demographic analysis was carried out on 1728 records of Jersey crossbred cows maintained at Eastern Regional Station (ERS), ICAR-NDRI, Kalyani, West Bengal over a period of 40 years (1980-2019). The survival rate was 79% in first lactation and followed a decreasing trend with lactation order. The stayability for first lactation was one; decreased in subsequent lactations. Stayability was noted as 0.365, 0.052 and 0.015 at fourth, eighth and eleventh lactation respectively, indicating that only 36.5, 5.2 and 1.5 % of cows remained in the herd in these lactation period. Approximately 79% of total cows present in the herd belonged to first 4 lactations while less than 3% cows belonged to 9 and above parities indicating abundance of younger cows. The expected herd life was observed as 2.75, 2.222 and 1.721 in first, third and fifth lactation and decreased with parity order. The probability of cow being lost from the herd after first lactation was 21%. The present study concluded that the herd comprised of younger cows with a required annual replacement rate of 21% to keep the herd size constant.