Calcium, non-phytate phosphorus and electrolyte balance in low-protein diet influence growth, tibia development and muscular protein deposition in medium-growing yellow-feathered broilers.

Excessive protein intake increases production costs and pollutant emissions in poultry production. As a result, low-protein diets supplemented with essential amino acids is considered a new normal. However, the mineral requirements in low-protein diet of broilers remain unclear. Therefore, an experiment was conducted to investigate the effects of different levels of calcium (Ca), non-phytate phosphorus (NPP), and electrolyte balance in a low-protein diet on the growth performance, serum parameters, tibia characteristics, muscular protein deposition and related gene expression in medium-growing yellow-feathered broilers from 1 to 30 days of age, in order to estimate the optimal dietary Ca, NPP, and electrolyte balance. A total of 324 1-day-old Spotted-brown male broilers were randomly allotted to 6 replicate cages (6 chicks per cage) for each of 9 treatments in a completely randomized design involving a 3 × 3 factorial arrangement of treatments. The birds were fed a corn-soybean meal low-protein diet (19 % crude protein) containing 0.70, 0.80 or 0.90 % of Ca and 0.35, 0.40 or 0.45 % of NPP, and 200, 250 or 300 meq/kg of electrolyte balance, respectively. The increase of dietary electrolyte balance (DEB) from 200 or 250 meq/kg to 300 meq/kg increased (P < 0.02) final body weight, average daily gain, and average daily feed intake. The interaction between Ca, NPP, and DEB affected (P < 0.03) serum Ca, alkaline phosphatase activity, tibial breaking strength, as well as the crude protein content and mRNA expression levels of forkhead box protein O1 and O3, and myogenin and atrophy f-box in breast muscle. Increasing dietary Ca and NPP from 0.7 % Ca and 0.35 % NPP to 0.80 % Ca and 0.40 % NPP or 0.90 % Ca and 0.45 % NPP enhanced (P < 0.05) bone mineral density, bone mineral content and ash content in tibia. These results indicated that 0.9 % Ca, 0.45 % NPP, and 300 meq/kg DEB in a low-protein diet were optimal for growth, tibia development, and muscular protein deposition in medium-growing yellow-feathered broilers from 1 to 30 days of age.