Trop Anim Health Prod (2006) 38:511–519 DOI 10.1007/s11250-006-4419-zThe objectives of this study were to assess changes in nutritional status/body condition score, percentage pregnancy and calving rate in Zebu cows and to establish the relationship between body condition score loss and postpartum interval to resumption of ovarian activity. A total of 198 cows and postpubertal heifers of the Tanzanian Shorthorn Zebu kept under a traditional management system were randomly selected from 200 smallholder herds. Factors investigated during bi-weekly visits include body condition score (BCS), heart-girth circumference, milk yield and reproductive status of the animals, pregnancy/nonpregnancy and cyclicity/non-cyclicity. Local weather conditions and dates of occurrence of other reproductive events such as calving were also recorded. Calvings occurred all year round but with a strong seasonal distribution characterized by annual peaks observed between April and July. The annual calving pattern was closely related to rainfall, with peak precipitation occurring a few months before peak calving. The overall percentage pregnancy varied from 30% to 50% throughout the N. L. Kanuya ( ) · M. K. Matiko · R. Nkya · S. B. P. Bittegeko · M. N. Mgasa Department of Veterinary Surgery and Theriogenology, Faculty of Veterinary Medicine, Sokoine University of Agriculture, Morogoro, Tanzania e-mail: nkanuya@yahoo.com O. Reksen · E. Ropstad Department of Production Animal Clinical Sciences, Norwegian School of Veterinary Science, Oslo, Norway year. Postpartum cows exhibited minimum mean BCS and heart-girth circumference 12–14 weeks after calving, and cows with BCS loss >1 point exhibited the longest time interval from calving to onset of ovarian activity.