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, tibi otarsal growth characteristics, and elastic modulus of proximal tibiot arsal subchondral cancellous bone in roaster chickens was investigated . Heavy meat strain birds were grown from hatch to nine weeks of age w hile being fed five dietary treatments with varying levels of protein and amino acids. The treatments included levels of protein and amino a cids varying from 80 to 120 % of the national recommended concentratio n (NRC), as well as an early protein and amino acid restriction treatm ent. The effects of dietary treatment, and indirectly the effects of m uscle mass development on body mass, tibiotarsal growth, bone mineral content, and elastic modulus of subchondral cancellous bone were measu red at one, three, five, seven, and nine weeks of age. The elastic mod ulus results were compared with bone mineral content measurements take n 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 gr eater than body mass for birds fed other treatments. However, properti es relating to mineral content decreased for all treatments at the har vest age of nine weeks, especially percent-ossified tissue and bone mi neral content. Increased levels of protein and amino acids are believe d to positively influence body mass and muscle mass; the early restric tion of protein and amino acids did not inhibit body mass or tibial gr owth. At nine weeks of age, dietary treatments that provided higher pe rcentages of amino acids than proteins displayed significantly lower m ineral contents and higher elastic moduli than other dietary treatment s. If the desired outcome is larger birds at harvest age without decre ased bone development, then the early restriction of protein and amino acids is recommended.