Abstract
Data on about 3999 records from 1990 to 2003 collected at artificial insemination center Mirpur city were utilized
for this study and analyzed using Harvey's Mixed Model Least Squares and Maximum Likelihood Computer
Program to study the environmental sources of variation on some performance traits of Desi /Iocal, F1 (Holstein
Friesian and Jersey X Desi), Holstein Friesian, Jersey and Sahiwal dairy cows of different genotype. The least
squares means for number of services per conception, age at first service and gestation period were 1.07±0.18,
990.37±239.24 days and 280.84±0.35 days, respectively. The coefficient of variation for these traits was 24.31,
21.97 and 1.71 percent respectively. The least squares means for daily milk yield was 8.72±0.18 liters with 32.42
% coefficient of variation. The analysis of variance for age at first service revealed that year and genotype showed
significant differences (P< 0.05), however, the season of birth had non-significant effect on age at first service.
Moreover, data revealed that the year of service and genotype have significant (P<0.01) influence on number of
services per conception during the study period, however, the season of service and parity showed nonsignificant difference. There was no significant difference due to age at service of the cows. The difference was
non- significant in the number of services per conception due to increase in the age of cow. It was further
observed that the gestation period in the present data set was significantly (P<0.05) different due to year / season
of birth, genotype, parity and sex of the calf born. The variability in daily milk yield was significant (P<0.05) due to
year of calving and genotype of animal, whereas, there was non significant difference in daily milk yield due to
increase in the age of animal. The conception rate was variable in different year, season, genotype and parities.
The mean conception rate during different season was 55.71 percent. It was the highest (79.63 %) during
summer and lowest on autumn (43.40 %). Conception rate was 62.55, 61.55, 58.33, 58.14 and 59.07 percent,
respectively in Desi, F1, Holstein Friesian, Jersey and Sahiwal cows. The calving rate was 70.55 percent of the
pregnant cows. It varies in different seasons of the year ranging from 53.804 percent in summer to 91.73 percent
in spring. The calving rate was higher in Holstein-Friesian (74.36 %) and lowest (60.00 %) in Sahiwal. It was
69.29 percent and 69.45 percent in Desi and F1 (crossbred), respectively.
