Abstract. Data from Zebu x Friesian crossbred dairy cows of different upgrading kept in the Kenana Sugar Company (KSC) farm, 300 km south of Khartoum on the bank of the White Nile in the low rainfall savannah region were collected over a period from 1984 to 2004 and analyzed using Harvey’s (1990) Least Squares programme. The results indicated that there were no significant differences in milk yield per lactation, daily milk yield and lactation between the 25% and 37.5% genetic groups. The 50% Zebu x Friesian group produced significantly more milk per lactation (2721.10 ± 87.36 kg) compared to the 25% and 37.5% groups (2067.20 ± 241.62 and 2192.68 ± 122.66, respectively). The milk yield per lactation and daily milk yield of the 50, 62.5, 75 and 87.5% breed groups was not significantly different. There were no significant differences in length of lactation between the 25%, 37.5% and the 50% group (267.99±18.14, 273.11±9.25 and 278.75±6.52, respectively). Groups with 75% and 87.5% of Friesian blood proportion had significantly longer lactation days (305.09 ±10.63 and 347.07 ±30.14, respectively). The range for dry period was between 78.37±12.27 days for the 75% genetic group to 92.56±16.76 days for the 25% group.

The mean calving intervals for the five genetic groups ranged from 367.85±21.38 days for the 75% group to 394.60±16.33 days for the 50% group. The earliest age at calving (41.56±2.16 months) was achieved by the 37.5% group while the latest age at first calving (49.01±1.29 months) was recorded for the 62.5 % group. The results of this study and other similar studies in tropical countries provide proof that the local environment (i.e. high temperature, low feed quality and quantity, disease and parasitic loads) can sustain composite genotypes of up to 50% B. taurus blood and does not lead to significant yield increases in upgraded groups. The economic feasibility of raising crossbred cows (Zebu x Bos taurus) under the Sudan condition has to be further evaluated in comparison with native dairy breeds to determine the overall efficiency and economic benefits.