8 

 factors are those which are present in the diet and include 

 actual concentration of the diet, chemical or physical form of 

 the element, presence of chelating agents, solubility of the 

 source, presence of interacting nutrients, and protein 

 concentration of the diet (Vohra and Kratzer, 1964; Rosenberg 

 and Solomons, 1984; Stuart et al . , 1986; Shafey et al . , 1991). 

 Overall, the extrinsic factors can be controlled more 

 efficiently to improve bioavailability. 



The many factors which have been studied for their 

 possible effects on bioavailability include levels of 

 supplementation of an element (Ammerman and Miller, 1972), 

 elements supplied by different foods (O'Dell et al . , 1972), 

 different inorganic sources (Wedekind and Baker, 1990; 

 Sandoval, 1992), and organic sources (Hill et al . , 1986; 

 Pimentel et al . , 1991; Wedekind et al . , 1992). Also, 

 adsorption of minerals to macronutrients , binding of minerals 

 to other compounds, and oxidation/reduction reactions may take 

 place (van Dokkum, 1989) . There are also individual genetic 

 or physiological defects which can determine the absorption, 

 or lack thereof, for any particular nutrient (Rosenberg and 

 Solomons, 1984) . 



Assessment of Trace Element Bioavailability 



O'Dell (1983) suggested that the best way to assess 

 bioavailability was to compare absorption and utilization in 

 a feedstuff with those in a standard soluble salt of the 



