42 

 Serum Zn concentrations increased with supplementation, 

 but these levels did not decrease during the month of 

 depletion. Therefore, it is impossible to speculate from 

 these data about tissue Zn retention by the different 

 treatment groups. Increased retention of Zn in lambs fed 

 ZnMet had been shown to be greater than that from ZnO 

 treatment (Spears, 1989) . Mean serum Zn levels were different 

 on d 49 and 55. Furthermore, on d 55 Zn levels for the ZnLys 

 treatment had increased more from d 1 than those of all 

 treatments except ZnS0 4 . This may imply a higher 

 bioavailability for these two sources. 



Serum Cu concentrations dropped slightly during the 

 trial. This was unexpected since the basal diet contained 

 around 70 mg/kg Cu to prevent the adverse effects of the high 

 levels of Zn supplementation. Since serum Cu content was not 

 lowered by the high Zn content of the Zn supplemented 

 treatments, this suggests different absorption routes for 

 these elements. Furthermore, decreased serum Cu levels were 

 unexpected because of the accumulation of Cu in the liver of 

 all the animals. Therefore, the low serum Cu may have 

 resulted from low hepatic Cu mobilization. There were, 

 however, no signs of Cu toxicity in any of the animals 

 studied. 



The data suggest that ZnLys has greater bioavailability 

 as a source of supplemental Zn . This suggestion is made on 

 the basis of greater accumulation of Zn in the liver, kidney 



