3 

 a need to investigate the effect of these different sources on 

 increasing concentrations of these minerals in the various 

 fluids and tissues of the animal's body. 



Zinc methionine, for example, has been determined to 

 bypass ruminal degradation (Heinrichs and Conrad, 1983). 

 Furthermore, since Zn is bound to methionine, it does not 

 combine with any other substrate which may make it unavailable 

 in the lumen of the animal and therefore it is ready for 

 absorption as soon as it enters the small intestine. On the 

 other hand, Spears (1989) observed that when Zn was deficient 

 in the diet, apparent absorption of Zn from either Zn 

 methionine or Zn oxide was similar. Zinc retention, however, 

 was higher in the lambs fed the Zn methionine, this suggests 

 a difference in the metabolism of these two sources following 

 absorption. It has been hypothesized by Spears et al . (1991) 

 that certain trace mineral chelates or complexes may enter 

 different pools in the body than the inorganic forms. 



In determining which parameters to evaluate for Zn and Cu 

 metabolism research, it has been shown that the majority of 

 biologically available Zn and Cu is stored in the organs of 

 the body such as liver, kidney and pancreas with minor storage 

 in the bone, muscle, skin and hair, although the latter two 

 storage sites are not readily available to the animal. Blood 

 plasma and blood cells serve as immediate sources of stored Zn 

 and Cu . Furthermore, dietary Zn seems to affect the synthesis 



