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Enhancing sustainability through reduced dietary protein via net energy

Kidd, M. and M. Costa

As more feed grade amino acids become available for formulation in broiler diets, the key challenge of meeting live performance and carcass traits as diet protein supply is lowered mimics the fundamental challenge of the past. Hence, the addition of each limiting feed grade amino acid in broiler diet formulation minimizes nitrogen excesses by closer meeting the most limiting amino acids in the nutrient matrix, but introduces concerns in terms of amino acid absorption, limitations of the less limiting essential or non- essential amino acids, or an imbalance of overall dietary protein and calories. Regarding the latter, as feed grade amino acids enter the ingredient matrix, soybean meal is reduced and birds consuming diets reduced in CP almost always exhibit an increase in peritoneal cavity fat. Is the associated increase in carcass adipose tissue a reflection of feed grade amino acid increased absorption resulting in bird imbalances, a reflection of more dietary grains (e.g., starch) resulting in an energy imbalance, a reflection of not adjusting dietary energy needs as protein supply is lowered, or a combination of the former? The understanding of dietary energy is compounded by the fact that commercial broilers are selected for leanness resulting in heightened responsiveness to amino acids as compared to that of energy. Recent research has focused on dietary variations of CP and net energy (NE). Ross 708 broilers were fed either 20.2 or 22.5% CP diets balanced with ME or NE from 7 to 32 d of age. Live performance and processing differences were minimal, but a CP x energy interaction occurred indicating that the increase in carcass fat caused by feeding reduced CP could be reversed with NE balance vs ME. Additional work demonstrated that Cobb broilers fed varying CP and NE from 31 to 41 d of age resulted in minimal interactions, but increasing NE decreased feed intake and feed conversion.

Thus, increased carcass fat caused by decreased CP in Cobb birds was not corrected with NE. Future work is needed to better understand NE levels for commercial broilers and subsequent interactive effects in low CP diets.