Fast-growing broilers have the potential to gain body protein quickly through nutrient intake during starter and grower periods. However, protein deposition requires adequate calorie intake in combination with digestible amino acids for maximum accretion. Research is needed to understand when and how much additional energy intake is needed for maxi- mum protein deposition in order to better design feeding programs for feeding phases. Two studies were conducted to determine the daily dietary energy utilization for protein deposition by using dual energy x-ray absorptiometry (DEXA). In Exp1, a total of 1440 fast-growing male broilers were randomly assigned to 48 floor pens and fed one of two test diets from d3 to d10 throughout an 8-day experimental period (8 trts; 6 reps). Each treatment consisted of feeding one diet (Diet 1) for a set period of days and then switching the diet to a higher energy diet (Diet 2). Diet 1 was formulated to Cobb 500 starter recommendations while the Diet 2 contained 50 extra kcals ME/kg and a constant protein to energy ratio, similar to the ratio in Diet 1. At d10, broilers were scanned to determine the dietary energy intake needed for maximum protein deposition. In Exp 2, a total of 1440 fast-growing male broilers were randomly assigned to 48 floor pens and fed one of two test diets from d10 to d17. As in Exp1, treatments contained two diets that were switched on different days. Diet 1 was formulated to Cobb 500 grower recommendations and Diet 2 contained an extra 50 kcals ME/kg and the same protein to energy ratio as contained in Diet 1. At d17, broilers were examined to determine the dietary energy intake needed for maximum protein deposition. Data was analyzed using JMP Pro 14 (SAS Institute, 2018). Exp1 showed lean mass and protein mass in- creased when the diet was switched a higher energy containing diet on d6 (P<0.05). Exp 2 determined that protein mass increased in the treatments that had diet changes on d11 and d16 (P<0.05).
These studies indicate that the increase in the daily intake of calories at certain days in starter feeding phase may be necessary to gain more protein mass with standard diets. Thus, protein deposition may require additional calorie densities and intakes in order to sustain the protein gain advantage.