Sixty growing lambs (30 of which were Rahmani and 30 were Ossimi) were
randomly divided into four groups (15 from each breed). Two concentrate levels (2.5
and 3.0% of body weight) were evaluated, while roughage was offered free choice for
animals. Concentrate was the traditional concentrate feed mixture (CFM) of which
80% was yellow com grains and had 77% TON. The experiment was conducted in the
north western coast of Egypt. Results revealed that increasing concentrate level (3% CFM) increased digestion coefficients of most nutrients and feeding values of the rations. Retained nitrogen also improved and blood total proteins albumin, globulin as well. Average daily gain increased as well as feed efficiency. There were no significant differences in rumen pH and total volatile fatty acids, Cost of producing the unit of growth (Kg) and economic efficiency were in favor of low concentfate level (2..5%). The breed effect was not significant. Generally, increasing the com grains in the concentrate feed mixture led to increasing TON value of the diets. However, the wider roughage to concentrate ratio represented by the 2.5% concentrate level is better than the other ratio for decreasing the cost of producing the unit of body weight gain. The pH values tended to decrease as the concentrate level increased, on the other hand the concentrations of TVFA's showed the opposite trend.