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Interrelationship of Molybdenum and Certain Factors to the Development of the Molybdenum Toxicity Syndrome ^l

University of Nevada, Reno

Abstract

Three levels of inorganic molybdenum, none (control),1.5 mg. (low) and 3.0 mg. (high) molybdenum per kg. body weight were administered to 24 steers on pasture. Molybdenum administration decreased body weights, increased plasma and liver molybdenum and caused achromotrichia and scouring. Molybdenum did not influence tissue levels of copper, but was associated with increased levels of liver iron. Molybdenum had no effect on plasma phosphorus or bone ash, molybdenum, calcium or phosphorus during the 100-day period.

Injections of copper glycinate at 100 days caused weight gains, reduction or elimination of scouring and a general increase in condition during an additional 50-day period. Copper injections significantly increased levels of plasma and liver copper and were also associated with an increase in hematocrit of those steers receiving molybdenum. Copper had no significant effect on plasma or liver molybdenum levels or plasma phosphorus.

Neither organic nor inorganic sources of molybdenum (207 to 222 ppm) caused apparent symptoms of molybdenum toxicity in rabbits. Higher levels of molybdenum in the ration increased plasma and liver molybdenum, plasma copper and bone molybdenum.

Methionine, sodium sulfate and sodium sulfite were similar in their ability to significantly alter plasma molybdenum levels of heifers. Plasma copper was not modified by any of these sulfur sources.

Molybdenum was rapidly taken into the blood of cattle. The greatest increase occurred between 24 and 48 hr., and a plateau was reached by 8 days. Daily administration of sulfate significantly decreased levels of plasma molybdenum, but had no effect on plasma copper. Daily administration of molybdenum maintained high levels of plasma molybdenum and caused plasma copper values to increase.

¹ Supported in part by grants from the Soil and Plant Nutrition Laboratory, U.S.D.A., Ithaca, New York, and the Society of the Sigma Xi, 91 Prospect Street, New Haven, Conn. Molybdenum was supplied by Climax Molybdenum Co., New York, N. Y.

² Present address: Nevada Agricultural Extension Service, University of Nevada, Winnemucca, Nevada.

³ Animal Science Division, University of Nevada.

⁴ Plant, Soil and Water Science Division, University of Nevada. Journal Series No. 25.