Effect of glutamic acid on broilers given submarginal crude protein with adequate essential amino acids using feeds...

Broiler males were examined for their response to feeds containing CP 1 to 2% below levels advocated by NRC (1994) and when supplemented with L-glutamic acid. Crude protein and glutamic acid treatments were imposed in starting, growing, and finishing feeds over 7 wk with K at high and low levels likely to occur in practice (0.80 vs 0.65 to 0.55%). All feeds were formulated to be isocaloric (3.20 kcal ME/g) and satisfy NRC (1994) essential amino acid (EAA) minimum requirements. Improved live weight gain occurred during the first 6 wk with supplementation of glutamic acid to the low CP feed but not when intact protein per se was used to increase CP. A similar advantage in growth was obtained from glutamic acid in response to its addition at equivalence of 1 to 2% CP as well as when dietary adjustments maintained low CP. Response to altered K could not be interpreted because of concurrent differences in glutamic acid and AMEn intakes. High glutamic acid levels did not decrease abdominal fat unless CP increased concurrently, whereas carcass back bruising and drumstick deformations were relieved by supplemental glutamic acid independent of CP. Increased weight gain from glutamic acid was only evident with drumsticks and debris that included the back when carcasses were cone-deboned. Supplemental glutamic acid is believed to improve the rate of connective tissue formation during rapid growth.