13 

 suitable physical forms (Ammerman and Miller, 1972). In 

 chicks, bioavailability of ZnO was determined to be 44.1% that 

 of ZnS0 4 (Wedekind and Baker, 1990). In another study 

 (Wedekind et al . , 1992) Zn methionine (ZnMet) was reported to 

 be better than both ZnS0 4 and ZnO. 



In cattle, ZnMet is not broken down by ruminal 

 microorganisms (Heinrichs and Conrad, 1983) and was found to 

 be more bioavailable than ZnO (Chirase et al . , 1991). In 

 pigs, however, ZnMet was found to be of equal bioavailability 

 with ZnS0 4 (Hill et al . , 1986). In lambs, ZnO and ZnMet were 

 absorbed to a similar extent, but were metabolized differently 

 after absorption (Spears, 1989) . In a summary of ZnMet 

 studies by Herrick (1989), ZnMet increased gain and feed 

 efficiency by an average of 3.5% in feedlot cattle. Also the 

 addition of ZnMet to diets of lactating dairy cows has 

 increased milk production and reduced somatic cell counts in 

 milk (Herrick, 1989; Kellogg et al . , 1989). 



In determining performance and mineral metabolism of 

 lambs, Kegley and Spears (1992) suggested ZnO and ZnS0 4 

 improved performance, but ZnMet had no effect. Chirase et al . 

 (1992) determined that Zn and Mn methionine improve the 

 recovery rates of calves stressed with infectious bovine 

 rhinotracheitis virus. In lambs, the retention of a Zn 

 proteinate source was higher than that of ZnO (Lardy et al . , 

 1993) . Visual hoof score and hoof durability have also been 

 suggested to be affected by Zn supplement (Moore et al . , 1992; 



