Comparative Performance of Imported and Home Bred Holstein Frieeian Cows.

Total Milk Production and Duration of Lactation

Abstract

A total of 3013 production records from Ghot Al-Sultan dairy cattle unit were used. The records were made by a mumber of imported cows and their locally born daughters. The differences between these two groups in 3X305, 2X305 milk yield and average daily milk yield were studied. In addition some general environmental factors were studied. The traits studied were total milk production and duration of the first three lactations. Leastsquares means of the three lactation were 7692.7 +61.5; 9383.6 + 74.5; 9731.6 88.2 and 8490.2 + 53.3, 9797.1 81.6, 9597.9 + 127.3 kg for importion and locally born cows consecutively. Duration of lactation was 293.0+ 2.5, 315.2 + 2.8, 323.9+ 3.3 and 350.6 + 4.2, 359.6 + 3.1, 372.6+ 4.5 consecutively. The results indicate significant (P<0.01) differences between the two groups in the first two lactations. Length of lactation differed significantly (P<0.01) in all three lactation. There was a significant (P<0.01) year of calving effect in the first lactation in the imported group and in the first three lactsations in the local group. Calving year effects on length of lactation were also significant at the same level in the first two lactations of the imported group and in the first lactation only for the local group. Season effects were highly significant (P<0.01), significant (P<0.05), length of lactation in the first two lactations only. linear, quadratic, and cubic regressions of total production on length of lactation were significant (P<0.01) in all lactations. Linear regression of total production on age at calving was not significant except in the third lactation.