Genetic and environmental effects on the productivity of Holstein-Friesiancattle under the climatic conditions of Central Sudan

A herd of 370 Holstein-Friesian cows were maintained in Central Sudan, Khar toum for intensive dairy production during the period 1990-1996. The area i s characterized by high temperatures during the day and cools down at night , with an average thermal-humidity index (THI) of 74.8. The average adjuste d lactation milk yield, milk yield per day, milk yield per day of calving i nterval and lactation length of the animals in the herd were 5117 +/- 123 ( SE) kg, 14.7 +/- 0.25 kg, 11.3 +/- 0.36 kg and 350 +/- 8.0 days, respective ly. Heifers calved at 25.2 +/- 2.3 (SD) months of age. The variation was la rge, which suggested large environmental fluctuations. Sire variance contri buted 1.35% and 19.6% to the total variance in cows and heifers, respective ly, while cow within sire contributed 19%. The heritabilities of total lact ation yield, 305-day yield, milk per day of lactation, milk per day of calv ing interval, and lactation length in heifers were 0.78 +/- 0.24, 0.36 +/- 0.34, 0.39 +/- 0.24, 0.23 +/- 0.23, and 0.23 +/- 0.22, respectively. In cow s, the heritability estimates were 0.05 +/- 0.24, 0.06 +/- 0.24, 0.08 +/- 0 .24, 0.00 and 0.00 for the same traits, respectively. The repeatabilities o f total lactation yield, 305-day yield, milk per day, milk per day of calvi ng interval and lactation length were 0.02 +/- 0.03, 0.22 +/- 0.03, 0.17 +/ - 0.02, 0.05 +/- 0.02 and 0.00, respectively. Regression analysis showed th at, for each unit increase in THI, milk yield decreased by 0.29 +/- 0.04 kg . The stress usually caused by the combined effects of temperature and humi dity was not severe in this area.