Abstract
The study aims at improving the utilization of olive cake (OC) containing-diets for laying hens by citric acid supplementation at 0.1 and 0.2%. Olive cake was collected and dried by sunny warm air at an average temperature of 45 degrees C with continuous stirring until completely dried. Then, the OC was included in isonutritive diets at 0, 10 and 20%. Additionally, citric acid was added at 0, 0.1 and 0.2%. This resulted in 3(OC levels)x3(citric acid concentrations), producing 9 different treatments. Each treatment was represented by eight replicates of three laying hens each. The diets were fed to laying hens from 40 to 56 weeks of age. Olive cake inclusion up to 20% without citric acid supplementation in the diets of laying hens did not affect laying performance, egg quality or liver function indices, but 10% and 20% OC diets increased feed intake and impaired the feed conversion ratio (FCR) compared with the control group. Citric acid added at 0.1% to the diets of laying hens containing 20% OC yielded similar FCR to the unsupplemented control. In addition, citric acid supplementation at 0.1% significantly decreased relative weight of liver compared with the other levels of citric acid, which is obvious in OC-free diet, and it significantly increased relative weight of ovary compared with the control diet, which is obvious in different diets. In conclusion, OC could be used in the laying hens' diets at 20% when supplemented with 0.1% citric acid without negative effects on laying performance, egg quality and blood metabolites.