A trial was conducted to determine the efficiency of utilization of rumen inert fat as a supplementary energy source for reproducing South African Mutton Merino ewes (n = 56) grazing wheat stubble.  The ewes were randomly divided into four groups of 14 ewes each, with every group representing a treatment.  The wheat stubble paddock was divided into four paddocks of equal sizes, and the ewes grazed these paddocks at a stocking density of 4.6 ewes/ha from the 1 November 1992 until May 1993 after the break of the season. The ewes were rotated between the paddocks on a weekly basis.  Each group received 250 g of supplementary feed per head daily for the last six weeks of pregnancy, and this was increased to 360 g during the first four weeks of lactation.  Supplementation was supplied on Mondays, Wednesdays and Fridays for a 70-day period.  Supplementary feed contains either inert fat, starch (maize meal), a combination of inert fat and starch or wheat bran as an energy source.  The crude protein concentration of the supplements varied between 167 and 196 g/kg feed.  No significant difference occurred between the live weights of ewes during the last six weeks of pregnancy, the first four weeks of lactation, or the total feeding period.  The ewes receiving the 50% fat plus 50% maize meal tended to lose less weight during lactation than the ewes that received maize meal as their main energy source.  No significant difference occurred in the absolute live weight of ewes over the experimental period.  A lack of response to inert fat as supplementary source in the live weight of the ewes was observed during the total experimental period, when compared to the control group which received wheat bran.