T. E. ALI, F. A. AHMED AND Y. A. OMBABI
Department of Animal Science, Faculty of Agricultural Sciences, University of Gezrra P. 0.801 20, Wad Medani, Sudan.
SUMMARY
One hundred and nine, fourteen and ten first parity Friesian X Zebu cross-bred cows having respectively 50%, 62.5% and 75% Friesian blood were used. Most of the cross~breds were from Kenana dams and few were from Butana. All the 50% and 75% cross-breds were from the Nisheishiba Farm while all the 62.5% cross-breds were from the Univer- sity of Khartoum Experimental Farm. The objectives of the research were to study the effect of percent of Friesian blood, age, year and season of calving on productivity of cross-bred cows, and to determine the relation- ship among these productivity traits. Lactation yield and lactation length were highly significantly (P < 0.01) affected by percent of Friesian blood. Lactation yield was the only trait to be significantly (p < 0.05) affected by the age covariate. Both lactation yield and lactation length showed no clear seasonal or yearly trend. Daily milk yield and age at first calving were not significantly affected by any of the factors studied. Lactation yield had significant (P < 0.05) positive correlation with lactation length. The values of those correlations were 0.78, 0.60 and 0.94 for the 50%, 62.5% and 75% cross-breds respectively. Lactation yield was also highly positively correlated with daily milk yield with values ranging from 0.77 to 0.84. Lactation yield however, was lowly correlated with age at first calving. The correlation of lactation length was low with daily milk yield and not significant with age at first calving. The correlation between daily milk yield and age at first calving was positive for the 50% (0.15) and 75% (0.82) but negative for the 62.5% (- 0.48) cross-bred cows. Based on the results of this study it is suggested that the 50% Friesian blood would be the grade of choice under the Sudan tropical condition.
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