Dorper and Blackhead Persian ewes and ewe lambs were grazed on veld during the day and fed varying amounts of cottonseed meal when kraaled at night. The teeth were examined weekly when the sheep were weighed and eruption of permanent incisors recorded. All the Blackhead Persians’ permanent incisors erupted earlier than the corresponding pairs in the Dorpers regardless of the level of nutrition. Within breeds, supplementary feeding of cottonseed meal significantly decreased the time taken for eruption of all permanent incisors. The group in which both ewes and lambs were supplemented had the shortest eruption time, followed by that in which ewes were supplemented but lambs not, and the longest time was taken by that group receiving no supplements at all. Average daily gain is inversely related to eruption time, as shown by the negative (overall) correlation coefficients, and Blackhead Persians appear to be less affected by the level of nutrition than Dorpers.