Genetic and environmental effects upon reproductive performance of Holstein crossbreds in the Sudan.

Data from a herd near Khartoum for 1955 to 1977 were evaluated. Climate was semidesert with most rainfall (151 of 165 mm) in July through September. Mean maximum daily temperatures ranged from 30.7 (January) to 41.1 degrees C (May); mean minima were 14.6 degrees C (January) and 26.9 degrees C (June). Original base population (1907) was Butana with additions of Butana, Dairy Shorthorn, Ayrshire, Guernsey, and Holstein. Breed groups and % Holstein were 1, 0 to 25%; 2, 26 to 49%; 3, 50%; 4, 51 to 71%. Numbers and mean performance were gestation length, 2474, 279 d; services per conception, 2403, 2.07; calving interval, 4004, 441 d; days open, 3204, 165 d. Calving intervals (1689) were shorter for Group 3 -25 to -31 d as were postpartum days open (-27 to -31 d), and number of services per conception was lower (.21 to .37). These animals were Holstein by Butana crossbreds, so their superior performance could reflect effects of heterosis. Gestation lengths were affected by month of parturition (January greater than June, 5.6 d), which also affected services per conception (March greater than August, .75 services). Over time, not gestation length but services per conception, calving interval, and days open increased. Repeatabilities and heritabilities for these measures were .14 and .07; .07 and 0; .10 and 0; .07 and 0. Phenotypic correlation between days open and calving interval was .99 and with gestation length was -.12. Other phenotypic correlations ranged from -.01 to -.04. Heritability of age at first parturition (888) was .31. Estimates were similar to those from temperate dairy areas.