44 

 with this treatment being very close to the control treatment. 

 These results indicate the lack of stimulus by the relatively 

 high Cu levels in the control and ZnO groups on MT levels. 

 The inability of Cu to act as a stimulus for MT induction is 

 well documented (Saylor et al., 1980; Peterson and Mercer, 

 1988) . Since MT present in sheep is not stimulated by Cu, 

 this may be one of the causes for their high susceptibility to 

 Cu toxicosis. Furthermore, the limited capacity of sheep to 

 synthesize MT in the intestinal mucosa (Saylor et al., 1980) 

 may also be a factor. This limited ability to block Cu 

 absorption at the intestinal level is supported by the high 

 levels of Cu in sheep livers in all treatments. 



Tissue Cu levels were not greatly affected by Zn 

 supplementation. There was a decrease from 30 to 50% in 

 muscle Cu concentrations for animals Zn supplemented compared 

 to controls, however. Copper muscle concentrations of 

 controls were probably due to one of two factors or both, the 

 high dietary Cu levels, or the low dietary Zn levels of the 

 control diet. A diet of 100 mg/kg Zn has been shown to 

 decrease liver Cu storage (Pope, 1971) . This decrease did not 

 occur in this experiment and actually the mean Cu content for 

 the control group was slightly lower (but not different) than 

 that of any other group. 



Metallothionein has been shown to bind Cu with a very- 

 high affinity. Therefore, Cu present in liver, kidney and 

 pancreas of the ZnLys treated animals is stored more in a 



