The influence of supplementary protein and phosphorus to Dorper and Merino wethers on native pasture was investigated over a period of one year. The supplements were provided by 2 different methods namely as a lick or at a constant daily level via rumen cannulae. Some of the observed differences in diet composition, digestibility and rumen NH3 concentration between the different treatments and breeds, were statistically significant (P ≤0,05). No definite trend due to any of the treatments could be found. Diet composition, digestibility and rumen NH3 concentration followed a seasonal trend in which rainfall played a dominant part.