An experiment was conducted to investigate the effects on the reproductive performance of lactating beef cows of supplementation with protein and/or energy during a 100 day period. Over three years the average recalving percentage for the cows receiving energy rich-, natural protein-, and non protein nitrogen supplements and for the Control cows was 96.0 per cent, 85.8 per cent 85,8 per cent and 73,1 per cent respectively. The average crude protein (CP) content of clipped grass samples for the summer, autumn, winter and spring periods was 5,88 per cent, 4,20 per cent, 3,80 per cent and 5,67 per cent respectively. The Ca and P content showed no great variation over the four seasons and averaged 0,17 per cent and 0, II per cent respectively. Based on an assumption concerning the average intake of a lactating beef cow and the chemical composition of the grass sward, it was estimated that the veld supplied 90 per cent, 65 per cent, 65 per cent and 42 per cent of the TDN, CP, Ca and P requiremen ts (NRC, 1976) of the lactating beef cow.