EFFECTS OF COBALT AND NICKEL ON ZINC AVAILABILITY IN CHICKS AND PIGS FED PRACTICAL-TYPE DIETS HIGH IN CALCIUM

Experiments were conducted with chicks and pigs to determine whether the sparing effects of cobalt (Co) or nickel (Ni) on zinc (Zn) nutrition were due to an improved Zn availability. They included a Zn balance study with New Hampshire X Leghorn cross chicks, a $^{65}Zn$ absorption study with Ancona chicks and a $^{65}Zn$ balance study with pigs. The basal diet was a corn-soybean type diet high in calcium. In the Zn balance study with New Hampshire X Leghorn cross chicks, Zn retention percentages for basal, + 54 ppm Ni or + 54 ppm Co were 39.4, 40.4 and 48.3, respectively. In the $^{65}Zn$ absorption study with chicks, adding these levels of Ni or Co to the basal diet increased $^{65}Zn$ absorption from 12.8% to 14.0% and 15.1%, respectively. Supplemental Ni and Co increased the proportion of body $^{65}Zn$ found in liver and bone. With the pig experiment, $^{65}Zn$ retention percentages for basal, +54 ppm Co and + 60 ppm Zn groups were 20.0, 26.7 and 12.2, respectively; while Zn retention values (mg) in the body were 29.5, 45.1 and 60.5, respectively. In addition, supplemental Co increased $^{65}Zn$ concentration in the blood, liver, kidney and duodenum. These studies showed that supplementation of the basal diet with Co resulted in increased absorption of dietary Zn in chicks and pigs. The effect of Ni in chicks was less than that of Co. The ability of supplemental Co and to a lesser extent of Ni to improve weight gain as well as reduce other Zn-deficient signs in both species fed a practical corn-soybean type diet high in in calcium can be explained, at least in part by an associated increase in Zn absorption. The possible mechanism involved in these effects are discussed.