Work done at N.C. State (J. Anim. Sci. 72:2722; another in preparation) suggested that iron levels of 600-800 ppm could produce copper deficiency in beef cattle receiving diets marginally adequate in copper.
High levels of Fe in drinking water can result in:
1. Decreased water intake due to palatability problems leading to a lowered milkyield,
2. decreased bioavailability of Cu (liver Cu remain low despite supplementation) with resultant poorer conception rates
3. there is an interaction with Mn, Se and Zn as well as Co - all of which, if deficient, may lead to fertility problems - according to the literature (NRC & Puls)
Mike Socha, Ph.D.
(612) 944-2749 (fax)
Excess iron will reduce the availability of some trace minerals such as copper or increase the requirement for trace minerals, such as zinc and vitamins such as vitamin E.
Iron is a very strong prooxidant. Jim Miller from the University of Tennessee has done some work looking at the effects of excessive amounts of iron prepartum on incidences of retained placentas, udder edema and post calving reproductive performance. He presented some of this data at the Eastern Nutrition Conference in Halifax, Nova Scotia in May of 1996 .
In the study cows received a basal diet containing roughly 100 ppm of zinc and 225 ppm of iron. He fed an additional 12 g of iron as iron sulfate (increased iron concentration to over 1100 ppm in the diet) with or without 800 mg of additional zinc (400 mg zinc from Zinpro's zinc methionine and 400 mg of zinc from zinc sulfate, increasing the zinc concentration in the diet to roughly 170 ppm of zinc) and with or without 1000 IU of vitamin E. Results of this study indicate that feeding additional iron increased saturation of the iron binding proteins and resulted in increased incidences of retained placentas and udder edema. Zinc and vitamin E supplementation decreased incidences of retained placentas under both levels of iron supplementation. However, when additional iron was not fed, vitamin E reduced the severity of udder edema, while zinc had no effect. When additional iron was fed, zinc reduced the severity of udder edema and vitamin E supplementation had no effect. Both zinc and vitamin E improved reproductive performance (reduced days to first estrus, days to first service, etc.) after calving. Results of this study indicate that during periods of oxidative stress, such as cows consuming excess iron, increasing the level of antioxidants in the diet, such as zinc, vitamin E, copper, etc will help minimize the effect of excess iron in the diet. Secondly, this study demonstrates that different antioxidants have different roles in minimizing the effect of iron as a prooxidants. In this study, increasing the supply of both vitamin E and zinc was beneficial.