*3.4. Bioavailability*

Relative bioavailability (RVB) of Zn sources was estimated based on the linear regression slope ratios of Zn concentrations and the activity of the Zn-dependent enzyme Cu/Zn SOD in lamb tissues regressed on the basis of Zn supplemental levels (Table 7). ZnSO4 used as the Zn standard was assigned a value of 100%. The slopes and estimated RBV values based on Zn concentrations in plasma, liver, and kidney as well as liver activity of Cu/Zn SOD did not differ among the Zn feed additives (*p* > 0.05). The best parameter for the assessment of RVB was Cu/Zn SOD activity in the liver ( *R*<sup>2</sup> = 0.44), and based on this parameter, RBV tended to be higher in lambs fed ZnGly (*p* < 0.085).

**Table 7.** Estimated relative bioavailability (RBV) of Zn sources based on linear regression slope ratios of Zn concentrations in tissues and liver activity of Cu/Zn SOD on Zn supplementation level (mg).


a Intercept = 0.57, *R*<sup>2</sup> = 0.16, and SD = 0.086; b Intercept = 118, *R*<sup>2</sup> = 0.33, and SD = 11.9; c Intercept = 106, *R*<sup>2</sup> = 0.23, and SD = 9.72; d

Intercept = 78.7, *R*<sup>2</sup> = 0.44, and SD = 24.6.
