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The influence of elevated dietary zinc, selenium, and their combination on the suppressive effect of dietary and intraperitoneal cadmium on egg production in laying hens.

The influence of elevated dietary zinc and/or selenium on the suppressive effect of cadmium on egg production in hens has not been previously established. To address this question, two models of cadmium administration were used to differentiate protective effects of zinc or selenium that may result from a reduced absorption of cadmium from those resulting from an elevated nutritional status of these minerals. First, cadmium-induced suppression of egg production was produced in White Leghorn hens using intraperitoneal injections of Cd in order to determine protective effects that result from prefeeding diets supplemented with 803 ppm Zn, 0.91 ppm Se, or their combination relative to a basal diet (control). Feeding elevated dietary selenium throughout the experiment, including a 6-day prefeeding period before Cd administration, resulted in significant protection from the egg suppression produced by 2 injections of cadmium (0.27 mg/kg each) given 1 d apart. Feeding elevated dietary zinc alone or combined with +0.91 ppm Se for a similar period did not markedly protect against cadmium-induced egg suppression. After a 0.54-mg/kg dose of Cd was administered, for a cumulative dose of 1.08 mg/kg, no significant protection was observed from any of the supplemented diets. In a second experiment, the protective effect of the same dietary treatments on the egg-suppressive effect of dietary cadmium was determined. In contrast to cadmium injection, the suppressive effect of 153 ppm dietary cadmium was not mitigated by selenium supplementation, while supplemental zinc protected against this effect of dietary cadmium regardless of the amount of selenium in the diet. There was no significant change in plasma estrogen and vitellogenin levels as a result of cadmium administration in either model, with the exception of significant reduction in both these parameters in the dietary cadmium-exposed birds fed the basal diet. Together, the data suggest that the level of dietary zinc in food sources may be more important in influencing cadmium-induced egg suppression than the nutritional status of zinc in cadmium-exposed birds. In contrast, the nutritional status of selenium in cadmium-exposed birds may have the potential to mitigate this effect, but high exposures to dietary cadmium or zinc may preclude such protection.