Serum total Ca in chickens at 21 d and 42 d
(Table 3) increased quadratically and linearly in response
to increasing dietary VD3, (P < 0.01), and only a
linear effect was found at 63 d. There were only modest
further responses beyond the 400, 500, and 600 IU/kg
of VD3, estimated as the requirements for the 3 growth
stages.