The zinc contents in tibia ash were used to calculate
the relative bioavailability of the organic zinc source
compared with zinc sulfate (reference). Therefore, linear
and quadratic responses were tested for each zinc
source first. Both zinc sources gave a linear response
(P < 0.05) up to the highest level of supplementation.
However, the response on the highest dose level for
zinc sulfate showed high leverage, i.e., showing a lower
response than expected based on the dose level. This
probably indicates that the plateau level was about to
be reached at a near adequate dietary zinc concentration.
As the 40 mg/kg of zinc sulfate treatment would
therefore reduce the slope for the reference, this highest
dose level was omitted from the slope analyses. The
linear slope ratio for zinc sulfate and organic zinc are
given in Figure 1. The following dose-response relationship
was found: