Low protein diets for broilers

A review of the literature regarding Low Protein diets (LCP) for broilers reveals that by using crystalline amino acids, dietary CP could be reduced in each phase safely by a factor of 10% (a figure fairly consistent with turkeys but quite low with that found for ducks and swine) from the respective NRC (1994) levels; the calculated minimum dietary CP levels thus appeared to be 20.7, 18.0, and 16.2% respectively for 0-21, 21-42 and 42-56 days of age. It is, however, noted that the magnitude of protein reduction, without affecting the growth performance of broilers, could have been increased depending upon the EAA concentration and balance of LCP vs. control-CP diets as well as the response criteria used (gain vs. composition of gain). Further reduction in dietary protein results in depressed live/carcass yield in almost all cases. Depressed feed intake appears partially to explain the negative effect of LCP diets in some cases. Addition of NEAA-like glycine above the current NRC recommendations has shown partially to alleviate the negative effect of LCP diets indicating imprecision of our knowledge about NEAA (like glycine, serine and proline etc) requirements of broilers under these conditions. The dietary NEAA/EAA ratio seems to be an important, though poorly understood, factor in defining the performance of broilers fed on LCP diets. It seems that regardless of the absolute amounts of dietary amino acids, performance tend to be depressed when NEAA/EAA ratio is decreased from 50/50; thus the NEAA level of about 50% of protein seems minimum state of adequacy. More work is needed before a precise role of the ratio of nitrogen coming from NEAA vs. EAA is proposed. A wider NE:ME in LCP diets seems to explain the higher body fat accretion on these diets; more work on how dietary NE:ME ratio modulates the growth performance of broilers, and how it interacts with different genetic stocks (lean vs. fat lines) is warranted.