9 

 element. Fox et al . (1981) suggested two indices of response, 

 primary and secondary. Primary indices of response include 

 quantifiable levels of morphology or physiological function 

 that indicate health, like measures of growth (height, weight, 

 head circumference, etc.), skeletal development (bone size, 

 conformation, and mineralization) , hematopoiesis , circulatory- 

 function, etc. Secondary indices of response are quantifiable 

 responses that do not measure health status directly but must 

 be correlated with primary indices under defined conditions, 

 like whole body retention or concentrations of inorganic 

 elements, metabolites, enzymes, or hormones in tissue, body 

 fluids, or excretory products. 



Comparisons of Organic and Inorganic Trace Element Sources 



The use of inorganic mineral supplementation sources is 

 well known throughout the industry. These products are used 

 by many animal industries for their feed products as either 

 direct mineral mixtures with the feedstuff or by manufacturing 

 a separate mineral supplement. One of the most important 

 factors determining the use of any particular source is its 

 bioavailability within the target animal. 



Zinc 



The nutritional essentiality of Zn was demonstrated first 

 in the rat (Todd et al . , 1934). Nutritional interest in Zn 

 was increased when the element was found to be deficient in 



