Response of broiler chicks to different levels of dietary ideal protein and digestible valine to lysine ratios in the starter period

In order to evaluate the response of broiler chicks to different levels of dietary ideal protein (Ross 308 strain recommendation and 10% less) anddigestible valine to lysine ratio (71, 74, 77, 80, and 83%) in the starter period (one to 10 days of age), a study was performed using 500-day-old malebroilers in a 2×5 factorial arrangements based on a completely randomized design including 10 treatments and 5 replications. The results showed thatreducing dietary ideal protein level increased body weight, feed intake and improved feed conversion ratio (P<0.01). The percentage of bone ash andcalcium content also increased significantly with decreasing dietary ideal protein (P <0.05). The reduction of the dietary ideal protein level decreasedthe concentrations of serum cholesterol, glucose, total protein, albumin, globulin, calcium, and phosphorus (P<0.05). The highest average body weightat 10 day of age, weight gain, carcass and breast percentages and the lowest feed conversion ratio were observed at 74% of digestible valine to lysineratio (P<0.05); while the highest average feed intake, thigh percentage, bone ash and calcium percentage were obtained at 77% of digestible valine tolysine ratio (P <0.05). No significant interaction was observed between the two experimental factors except for the carcass percentage traits (P<0.05)and serum phosphorus concentration (P <0.01). In conclusion, based on the results of this study, a 10% reduction in dietary ideal protein levels ispossible by maintaining ideal ratios of essential amino acids. The proper ratio of digestible valine to lysine is recommended to be 74% based onperformance indices and carcass traits, and 77% based on bone traits.