Evaluation of dietary calcium requirements for laying Longyan shelducks.

To establish the dietary Ca requirements for laying ducks during their peak laying period, 5 Ca levels (2.8, 3.2, 3.6, 4.0, and 4.4%) were used, and laying performance, eggshell quality, serum variables, and bone quality were examined. A total of 1,620 Longyan shelducks with similar BW at 20 wk of age were fed for 13 wk in 5 treatment groups, each with 4 replicates of 81 birds. Dietary Ca increased egg production and egg mass (linear, P<0.01) and reduced the feed conversion ratio (FCR), but egg weight was not affected. Dietary Ca level did not affect eggshell properties or any reproductive organ index except for shell weight (highest with the 4.0% Ca diet, P<0.05). Serum concentrations of Ca and calcitonin increased with dietary Ca level (linear, P<0.01), and a quadratic response (P<0.01) was seen in alkaline phosphatase activity; the highest values were in ducks fed the 3.6% Ca diet. Tibial fresh weight was affected by dietary Ca (linear and quadratic, P<0.05) with tibiae from the 2.8% Ca ducks weighing less than those from ducks fed any other Ca level. Other tibial measurements were unaffected by dietary Ca. According to the regression model, the Ca levels required for laying Longyan shelducks during their peak laying period are 3.4 and 3.2% for maximal serum alkaline phosphatase activity and tibial fresh weight, respectively. The results showed that diets containing 3.2 to 3.6% Ca provide for superior productive performance and bone quality in laying Longyan shelducks during their peak laying period.