الفهرس 
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Abstract
Twenty lactating Zaraibi goats in 2nd - 3rd season of lactation and average live body weight of 37.5±0.41 kg were used to determine the effects of inclusion (partially or totally) three levels of distiller dried grains with soluble (DDGS) instead of un-decorticated cotton seed meal (CSM) and small part of yellow corn on their productive performance. The experimental period lasted for 98 days after weaning. Goats were randomly assigned into four groups (5 goats each). Animals were fed according to NRC (1981) recommendations, since 50% of total protein requirements was covered from whole corn silage (WCS) and the other 50% were assigned at rations to receive the following formulated concentrate feed mixtures : R1 concentrate feed mixture ( 0.0 DDGS, CFM1) control ration, R2 (8% DDGS, CFM2) , R3(16% DDGS , CFM3) and R4 (24% DDGS, CFM4) to formulate approximately four isonitrogenious and isocaloric rations. Results showed that nutrient digestibility coefficients and nutritive values in terms of TDN, DCP % and DE, ME ( MJ/ kg DM) were significantly (P<0.05) improved gradually by adding DDGS levels to the tested rations. Inclusion DDGS at higher level in R3 and R4 rations lowered (P<0.05) ruminal pH values at all sampling times. Ruminal ammonia-N concentrations were significantly higher (P<0.05) with DDGS rations than the control one. Increasing level of DDGS improved average daily milk yield (ADMY) and its composition. The highest ADMY was recorded with R4 followed by R3 rations, while R1 recorded the lowest value . Milk fat and protein% were the highest for groups fed R3 and R4. Milk total solids% improved with increasing DDGS levels. The economic efficiency (EE) values cleared that DDGS rations (R3 and R4) reflected superiority over the control ration by approximately 10.9 and 23.5% for 16 and 24% DDGS levels, respectively . The obtained EE values in control and R2 rations were nearly similar (1.19 vs 1.21). from the nutritional and economical point of view the use of R4 (24% DDGS) to replace up to 100% of CSM in lactating goats rations could be recommended to improve goats performance and economic efficiency.