Directly after calving 62 Bonsmara cows were divided into one of the following groups: Group A served as a control and calves were allowed to remain with the cows and weaned at 7 months. In groups B, C and D the calves were weaned at 3 days of age, temporarily weaned for 12 days at 60 days of age, and permanently weaned at 60 days respectively. Cows were examined rectally three times per week to determine post partum uterine involution and the onset of ovarium activity. No difference could be detected between groups regarding uterine involution. Group B had a significantly shorter post partum anoestrus period compared to the other groups. Group A had an ADG of 0.197 kg from calving to first corpus luteum post partum, group B 0,744 kg, group C 0,207 kg and group D 0,352 kg. Lactation had a greater influence on the duration of post partum anoestrus than gain in body mass.