The incidence of oestrus, ovulation. fertilisation and embryonic mortality were investigated in a series of experiments. In the first experiment, the occurrence of oestrus and ovulation in Africanders and Hereford cows were compared. It was found that Africanders showed oestrus more irregularly than Herefords. In 8,5% of cases. Oestrus was not accompanied by ovulation, but these cases were usually found to be mid cycle heats falling between two normal oestrus periods. In an experiment under extensive conditions it was observed that 72% of dry Africander cows and heifers mated within the first three weeks of the breeding season and 95% within nine weeks. Only 67% conceived. Negative correlations of environmental temperatures and conceptions indicated a close inverse relationship between high temperature (> 30°C) and successful mating. A comparison of the number of ova found to be fertilized (87.5%) 3 days after mating in 8 cows. and the number of pregnancies (62,5%) in 16 cows of the same group suggests that embryonic loss could make a significant contribution to low calving percentages.