CHAPTER 3 



RELATIVE BIOAVAILABILITY OF ZINC METHIONINE 



AND TWO INORGANIC ZINC SOURCES 



FED TO CATTLE 



Introduction 



Several products offering minerals in chelated form or 

 complexed with amino acids are available for mineral 

 supplementation. Zinc methionine (ZnMet) can bypass rurninal 

 degradation (Heinrichs and Conrad, 1983) . Furthermore, it 

 does not combine with any other substrate which may render it 

 unavailable in the lumen of the animal and, therefore, it is 

 ready for absorption upon entering the small intestine. 

 Spears (1989) found that when a deficient diet was fed, 

 apparent absorption of Zn from ZnMet or ZnO was similar, but 

 Zn retention increased by ZnMet suggesting different 

 metabolism following absorption. Spears et al . (1991) 

 hypothesized that organic sources enter different body pools 

 than inorganic forms. The popular Zn sources used by the 

 animal feed industry are ZnS0 4 (36% Zn) and ZnO (72% Zn) ; 

 therefore, it is necessary to test other products against 

 those currently being used. 



The majority of bioavailable Zn when supplemented in 

 relatively high levels is stored in body organs such as liver, 



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