Study of Some Aspects of the Performance of Friesian Cross-Bred Dairy Cattle Under University of Khartoum Farm Conditions.

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Nahid Moahmed Tawfik, Fawi
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Some aspects of the performance of the Friesian cross-bred herd of the University of Khartoum's Farm were put under study. The data consisted of a total of 435 lactations through 8 successive years, during the period 1973 - 1991. The foreign blood percentage varied between 25%, 62%, 50% and 75%. The managemental procedures of the farm were recorded, and the data was statistically analyzed. Lactation curves of the 8 successive lactation years were constructed. The three major components of the curve: istency, lactation length, and peak yield were studied. The longevity and breeding efficiency of the herd were also calculated. Maximum milk yield, (lb) was reached in the 8th lactation. Within a lactation period, the maximum yield was attained in the 2nd month for the period and lactations studied. The average initial milk yield was maximum in the 5th lactation followed by the 7th lactation. The average monthly maximum and average 180 days yield was highest at the 7th lactation. Rate of decrease through the 7th lactation was highest, 60.7%. The correlation between rate of decrease and average monthly maximum yield was 0.7439. Average persistency of the total herd was 1.43±0.104 and the coefficient of variation was 7.3%. Persistency was maximum for the 1st lactation, thereafter it decreased. There was no difference among persistency values of later lactations. For late winter calvers, persistency was maximum. The early summer, late summer and early winter calvers showed no significant difference. Generally season of calving did not affect persistency. The average total milk yield was maximum for winter' calvers. Persistency of cows with high level of production was higher (1.5±0.4) than either medium(1.29± 0.4) or low producers (1.30± 0.2). The average lactation length was 374.63±39.2 days, coefficient of variation 10.1%. Lactation length was maximum at 1st lactation, 426.7 days and decreased slightly thereafter. There wasn’t much variation among later lactations. Generally there was no significant effect of age on lactation length. Lactation length affected the average total milk yield. Yield for cows with lactation length ≥13 months gave maximum yield followed by 11 - 12 months and ≥10 months group. The average weekly peak yield was 203.78 lb. The maximum average weekly peak yield was attained in the 7th lactation. 75.6% of the herd reached their peak milk yield in 1-8 weeks from the date of calving, 19.1% reached their peak in 9–15 weeks, and 5.3% in > 15 weeks from calving. The average productive life (longevity) was 2.404 lactations, and the average breeding efficiency 76.4%. The correlation between breeding efficiency and longevity was 0.1548. Longevity was found to decrease with increase of age at 1st calving. The regressions of average total milk yield on average persistency, average monthly maximum and average lactation length were 0.3727, 0.7523 and 0.0131, respectively. This indicates that for the herd under study, persistency followed by lactation length was of low effect on the lactation curve, with the peak production being the prominent feature of the lactation curve
Performance,Friesian Cross,Bred Dairy Cattle,, Khartoum Farm Conditions.