Most broiler nutrient requirement suggestions are given to maximize growth rate and minimize feed conversion ratio (FCR). Economic return and profit analysis are often neglected. In a previous study, we found that 20% amino acid (AA) reduction increased FCR in all 5 commercial broilers tested, but the cost of feed required to correspondingly increase BW was decreased in 4 out of the 5 strains. In the current study, a randomized complete block design with a factorial arrangement of 12 treatments (3 ME × 4 AA) was used. The 3 ME levels were 100, 92, and 84% of the commercially recommended level. The 4 levels of digestible AA (lysine, TSAA, and threonine) were 100, 90, 80, and 70% of the recommended level. A total of 864 Ross × Ross 708 broilers were randomly allocated to 6 blocks. Each block contained 12 pens with 12 birds per pen. Data were analyzed using a two-way ANOVA. Significance level was set at P < 0.05. Mortality was not affected by any treatments (P > 0.05). The combination of lowest dietary AA level (70%) and highest ME level (100%) resulted in the lowest BW from d 10 (P = 0.003) and through the remainder of the study period, including d 24, 34, 41, 48, and 55 (P = 0.007, 0.009, 0.006, 0.0004, and 0.002, respectively). Birds fed 70% AA exhibited higher FCR from d 10 to 24, as compared to birds fed 80, 90, and 100% dietary AA (P < 0.0001); however, the 70% of AA decreased FCR from d 48 to 55, as compared to 90 and 100% AA (P = 0.024). The lowest ME level (84%) increased FCR from d 41 to 48 (P = 0.015). Due to the lower cost of feed with lower AA and ME, the economic return to produce the same amount of BW on d 41 was increased by feeding the birds 70 and 80% AA as compared to 100% AA (P = 0.007); similarly, the economic return on d 55 was increased by feeding the birds 70 and 80% AA as compared to 90 and 100% AA (P < 0.0001). The economic return was also increased by feeding the birds 84 and 92% ME as compared to 100% ME on both d 41 and 55 (P < 0.0001).
In conclusion, adequate dietary AA is critical for early growth of young birds, and adequate ME is critical to feed utilization in older birds. Economic profit depends not only on growth rate and feed conversion efficiency of the birds, but also on the cost of the feed.