Interactive effect of dietary calcium and phytase on broilers challenged with subclinical necrotic enteritis: 3. Serum calcium and phosphorus, and bone mineralization

Calcium is chelated by phytic acid and forms phytate-mineral complexes reducing Ca availability and the ability of phytase to hydrolyze phytate. An increased Ca concentration in the gut favors the activity of <i>Clostridium perfringens</i> (<i>C. perfringens</i>). Therefore, it was hypothesized that high dietary calcium with high dietary phytase would decrease serum Ca and P and bone mineralization during necrotic enteritis occurrence. A total of 768 one-day-old Ross 308 male chicks were randomly allocated to 8 treatments with 6 replicate pens, each housing 16 birds. A 2 × 2 × 2 factorial arrangement of treatments was applied: dietary Ca (0.6 or 1.0%), phytase (500 or 1,500 FTU/kg), and challenge (no or yes). Half of the birds (384) were challenged with Eimeria spp. on day 9 and <i>C. perfringens</i> strain EHE-NE18 on day 14 and 15. Blood was collected from 2 birds per pen to determine Ca, P, and parathyroid hormone in the serum. The middle toe, tibia, and femur were excised from 2 birds per pen on day 16 and 29 for determination of ash, breaking strength (BS), and mineral concentration. The challenge decreased (<i>P</i> < 0.05) serum Ca⁺ in birds regardless of dietary Ca level (day 16). There was a challenge × Ca interaction (<i>P</i> < 0.05) for tibial BS (day 16), with challenge being more severe in birds fed high Ca than low Ca diets. A challenge × phytase interaction (<i>P</i> < 0.05) was present for femur ash (day 16), with high phytase only increasing ash in challenged birds. The challenge decreased (<i>P</i> < 0.05) the BS of femur and tibia at each time point. Birds fed high dietary Ca had lower tibial Mg (<i>P</i> < 0.001), Fe (<i>P</i> < 0.001), Na (<i>P</i> < 0.001), and Zn (<i>P</i> < 0.05) concentrations (day 29). Altogether, high dietary Ca and phytase improved bone mineralization showing that attention to Ca and P nutrition and phytase matrix values is warranted when high levels of phytase are used.