Bakery waste (BW) is much cheaper than barley (20 to 40% the price of barley). Bakery waste and barley grain have similar chemical composition; they contain 99 and 97% organic matter (OM), 1.1 and 1.8% fat, 18 and 15% neutral detergent fibre (NDF) and 14.0 and 14.5% crude protein (CP), respectively (DM basis). The objectives of this study were to determine the effect of substituting BW for barley grain in high concentrate fattening diets for lambs on nutrient intake, growth and carcass characteristics. Forty Awassi lambs (21.75
1 kg) weaned at the age of 65 days were assigned randomly to four experimental fattening diets differing in BW ratio in a completely randomized design. The control diet (CON) contained 20, 60, 11, 7, and 2% (DM basis) wheat straw, barley grain, soybean meal, corn grain, and minerals and vitamin mix, respectively. Bakery waste substituted barley grain by 10, 20 and 30% of the diet DM in the LBW, MBW and HBW diets, respectively. The experiment lasted for 56 days. Dry matter intake (DMI) decreased (p<0.05) in LBW diet compared to the CON diet by approximately 10%. No further reduction in DMI was observed with the higher substitution levels. Metabolizable energy intake for the CON diet (3.6 Mcal/d) was also reduced (p<0.05) compared with LBW, MBW and HBW diets (3.4, 3.4 and 3.3 Mcal/d, respectively). Final body weight for lambs fed the CON diet (34.8 kg) was higher (p<0.05) compared with lambs fed the LBW, MBW and HBW diets (30.6, 32.0 and 31.1 kg, respectively). Growth rate for lambs fed the CON diet (232 g/d) was also higher (p<0.05) compared to lambs fed the LBW, MBW and HBW diets (170, 189, and 167 g/d, respectively). Feed to gain ratio was higher (p<0.05) for lambs fed the LBW, MBW and HBW diets (7.2, 6.6 and 7.3, respectively) compared with lambs that consumed the CON diet (5.7). Body weight gain cost was reduced by approximately 8% by the MBW and HBW diets as compared with the CON diet. Dressing percentage, full gut weight, empty gut weight and liver weights were all unaffected by the BW addition to the diets and averaged 48.9%, 6.8 kg, 2.8 kg and 0.444 kg, respectively. However, fat tail weight was increased (p<0.05) with the higher levels of the BW inclusion. In conclusion, substituting BW for barley grain reduced DMI and growth performance. However, when BW substituted barley grain at the 20 and 30% of the diet DM, body weight gain cost was reduced by approximately 8%.