LAUSR

The current dietary Ca recommendation of broilers is primarily based on the previous studies carried out more than 30 years ago. However, the modern commercial broilers are quite different from those more than 30 years ago. The present experiment was conducted to evaluate an optimal dietary Ca level by bone characteristics and Ca metabolism-related gene expression of broilers fed a corn-soybean meal diet from 22 to 42 d of age. A total of 252 22-d-old Arbor Acres male broilers were randomly assigned to 1 of 7 treatments with 6 replicate cages of 6 birds per cage for each treatment. Broilers were fed the corn-soybean meal diets containing 0.50%, 0.60%, 0.70%, 0.80%, 0.90%, 1.00% or 1.10% Ca for 21 d, and each diet contained 0.31% non-phytate P. The results showed that the mineral contents in tibia and middle toe bone, mineral density in tibia and middle toe bone, middle toe ash percentage, middle toe ash Ca percentage and tibia alkaline phosphatase mRNA expression level of broilers were influenced (P < 0.04) by dietary Ca level, and increased quadratically (P < 0.05) as dietary Ca level increased. The estimates of optimal dietary Ca levels were 0.55%, 0.60%, 0.70%, 0.72%, 0.63%, 0.66% and 0.70%, respectively, based on the best fitted broken-line, quadratic or asymptotic models (P < 0.02) of the above sensitive indices. These results indicate that the optimal dietary Ca level would be 0.72% to support all of the Ca metabolism and bone development of broilers fed the corn-soybean meal diet from 22 to 42 d of age.