Two trials with 27 pregnant Ossimi ewes and 15 from their successive born lambs were carried out to evaluate the effect of feeding urea treated corn with cobs (UCC) as 50% (T₂) or total replacement (T₃) of pelleted concentrate feed mixture (CFM) compared to the conventional diets (CFM) on its production and reproduction performance. Rice straw was offered separately from the concentrate. Evaluation criteria included DM intake and utilization, ruminal fermentation characteristics, milk yield, birth, weaning and marketing weight and feed efficiency.     This study was conducted during the summer season (May through September 2003). In the first trial, 27 Ossimi, ewes beginning 45 days before expected day of lambing were assigned to the control, T₂ and T₃ diets. The milk was measured on day 14 post partum and once every week up to the 12^th week. The growth experimental periods were 137 day in duration using 15 weaned lambs. The selected lambs were allocated to the same three diets.  In digestibility trial, 9 adult rams were allocated to the same three tested diets. In vivo digestibility, nutrients digestibility were different among diets. Feeding values (TDN) was greater for T₃ followed by control diet whereas the highest DCP was recorded for T₂. Feeding UCC had no effect on ruminal parameters in terms of pH, NH₃ and total FVA`s across the sampling time except for NH₃-N. The replacement of CFM by UCC resulted in insignificant higher (p≤0.05) lambs birth weight T₃ (3.44 kg) but lower milk yield T₃ (436 g /day). The lower birth weight of lambs of the control group (p ≤ 0.05) tended to grow faster and perform higher weaning as compared to the treated group. In the growth trail, feeding UCC diets reduced ADG by approximately 10% compared to control. The results indicated that DM, TDN and DCP needed to produce 1 kg gain were almost 5 to 10% better than the corresponding items from T₂ and T₃. Replacement of CFM in pregnant and growing lamb's rations with UCC would be cost effective as cost of UCC is 60% less than the cost of CFM.