ABSTRACT
The objective of this study was to investigate the effect of partial substitution of protein in the ration by corn steep liquor (CSL) on milk production of Zaraibi goats and the manufactured white soft cheese. Twenty four Zaraibi does, at the beginning of pollination season weighing 37.5 kg and aged < 30 months, were selected and divided into four similar groups (n=6). The groups were assigned at random to receive four experimental rations. All goats offered treatment diets 30 days before the breeding season at flushing period then through pregnancy and lactation periods where the concentrate feed mixtures (CFM) was partially substituted by CSL at different levels: Zero, control diet (T1), 10% (T2), 20% (T3) and 30% (T4). The rice straw (RS) used as a roughage portion in all treatments and offered ad lib. The feeding experiment was extended for 34 weeks.
Results showed that supplementation of CSL at 20 and 30% of the CFM significantly improved both milk yield and composition. Total milk yield was significantly increased by 13.0, 21.0 and 37.8%, respectively for T2, T3 and T4 than control diet. Also daily milk yield was significantly increased with T2 (1.13 Kg/h), T3(1.21 kg/h) and T4(1.38 Kg/h) than control diet. Milk fat, protein and lactose percentages were significantly increased while milk total solid (TS) and ash content had insignificant increase by the tested treatments. The lowest values (P≤0.05) of fat, protein and lactose were recorded with control ration (3.02, 2.68 and 4.63%, respectively). The data of milk quality indicated that pH value was higher (6.77) with control group compared with the three levels of CSL. Soft white cheese had increased (P≤0.05) with all treatments during storing period in ash, salt contents, acidity and ripening indices while increase was insignificant with fat content. On the other hand, moisture content, yield and pH value were significantly decreased with increasing storage period. The texture characteristics revealed that cheese made from treated groups, T3 and T4 recorded higher values (P>0.05) for hardness, cohesiveness, gumminess and chewiness and the lowest values of springiness compared to other milk treated cheese at the beginning or end of storing. Sensory evaluation of cheese from animals fed 30% CSL (T4) gained significantly (P≤0.05) the highest total scores followed by T3 then T2 and T1 throughout the storage of ripening. The specific "goat flavor" taste was significantly improved in T4 and T3. Therefore, partial replacement of protein of concentrate feed mixtures (CFM) by CSL, especially at rates 30 or 20% could led to improve milk quality and yield and gain the best composition and texture properties of soft white cheese during ripening time.