GENETIC AND PHENOTYPIC CORRELA TIONS FOR SOME ECONOMIC TRAITS IN DAIRY CATTLE

Data on lactation records of 1113 purebred Sahiwal and 784 Holstein Friesian X Sahiwal (FS) and Jersey X Sahiwal (JS) crossbred cows kept at the Livestock Production Research Institute (LPRl), Bahadurnagar, District Okara and Qadirabad District Sahiwal for the period 1973-1995 were analysed to study genetic and phenotypic correlations among various productive and fertility traits. Eight traits of economic importance including age at first calving, lactation length, 305-day milk yield, total milk yield, milk yield per day of calving interval, calving interval, dry period and service period were studied. The overall means for age at first calving, 305-day milk yield and lactation milk yield were 1163 ± 188.9 days, 1755 ± 615.6 kg and 1848 ± 732.6 kg, respectively. Milk yield per day of calving interval averaged 3.81 ± 1.67 kg. The means for lactation length, calving interval, dry period and service period were 288 ± 70.5, 11 507 ± 110.2, 220 ± 118.3 and 227 ± 118.7 days, respectively. The genetic correlations (bivariate analysis) of lactation milk yield with 305-day milk yield, milk yield per day of calving interval, dry period, service period, calving interval and age at first calving were 0.82, 0.64, -0.96, -0.49, -0.56 and 0.63, respectively. The corresponding values for phenotypic correlations were 0.95, 0.78, -0.34, 0.27, 0.28 and -0.26, respectively. The genetic correlations of milk yield per day of calving interval by multivariate (tetravariate) analysis with lactation milk yield, 305-day milk yield, lactation length, calving interval, service period and dry period were 0.63, 0.87, 0.76, 0.95, 0.95 and 0.51, respectively. The corresponding values for phenotypic correlations were 0.96, 0:99, 0.70, -0.34, -0.33 and -0.64, respectively. The genetic and phenotypic correlations among other traits were also estimated from multivariate analysis and were compared with bivariate analysis.