Effects of Protein and Amino Acids on Poultry Growth and Bone Elastic Modulus

The effect of protein and amino acid levels and age on body mass, tibiotarsal growth characteristics, and elastic modulus of proximal tibiotarsal subchondral cancellous bone in roaster chickens was investigated. Heavy meat strain birds were grown from hatch to nine weeks of age while being fed five dietary treatments with varying levels of protein and amino acids. The treatments included levels of protein and amino acids varying from 80 to 120% of the national recommended concentration (NRC), as well as an early protein and amino acid restriction treatment. The effects of dietary treatment, and indirectly the effects of muscle mass development on body mass, tibiotarsal growth, bone mineral content, and elastic modulus of subchondral cancellous bone were measured at one, three, five, seven, and nine weeks of age. The elastic modulus results were compared with bone mineral content measurements taken at the same ages and the same dietary treatments. Early protein and amino acid restriction did not adversely affect marketable body mass; instead, body mass at harvest age for birds fed this treatment were greater than body mass for birds fed other treatments. However, properties relating to mineral content decreased for all treatments at the harvest age of nine weeks, especially percent-ossified tissue and bone mineral content. Increased levels of protein and amino acids are believed to positively influence body mass and muscle mass; the early restriction of protein and amino acids did not inhibit body mass or tibial growth. At nine weeks of age, dietary treatments that provided higher percentages of amino acids than proteins displayed significantly lower mineral contents and higher elastic moduli than other dietary treatments. If the desired outcome is larger birds at harvest age without decreased bone development, then the early restriction of protein and amino acids is recommended.