14 

 Reiling et al . , 1992). Although hoof growth and wear 

 measurements were similar for ZnMet supplemented dairy cows 

 versus controls, visual hoof score (texture, heel cracks, 

 laminitis, ulcers, interdigital dermatitis and hoof rot) 

 showed improvement with ZnMet (Moore et al . , 1992). Hoofs 

 from Zn proteinate supplemented heifers had a higher shearing 

 force than those from ZnS0 4 supplemented animals (Reiling et 

 al., 1992). In young pigs, Hall et al . (1993) suggested 

 increased availability of ZnMet versus ZnO supplementation. 

 Rust and Schlegel (1993) reported no differences in steer 

 performance or carcass characteristics with ZnO or ZnMet 

 supplementation . 



Copper 



The nutritional essentiality of Cu was demonstrated first 

 by McHargue (1925) based on the wide distribution of Cu in 

 plant and animal tissues. Interest in Cu nutrition grew in 

 the 1930s when Becker et al . (1931) and Neal et al. (1931) 

 reported that Cu was responsible for a condition in Florida's 

 cattle known as "salt sickness." 



Copper has an atomic number 2 9 and an atomic weight of 

 63.55. Copper can exist as the metallic form or in +1, +2 or 

 +3 valence states. The most common is the +2 state (Miller, 

 1979) . It tends to occur in sulfide deposits, particularly 

 igneous rocks, with concentrations in the continental crust of 

 5 ppm . 



