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Journal of Dairy Science Vol. 60 No. 6 975-980
© 1977 by American Dairy Science Association ®
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Serum Thyrotropin and Thyroxine after Thyrotropin Releasing Hormone in Dairy Cows Fed Varying Amounts of Iodine1

E. M. Convey, L. Chapin, J. S. Kesner and D. Hillman

Department of Dairy Science, Michigan State University, East Lansing, MI 48823

A. R. Curtis

Michigan Department of Agriculture, Bureau of Consumer Protection, Lansing, MI 48913

ABSTRACT

The objective was to determine whether dairy cows fed relatively large amounts of iodine had altered thyroid status. In addition, polarographic analysis for determination of iodine and bromine in milk and urine is described. Five dairy herds fed an average of 16 mg iodine/head per day (range 11 to 25) and five fed 164 mg iodine/head per day (range 74 to 402) were identified. Iodine fed was estimated from minimal guaranteed iodine content of concentrates, iodized salt, minerals, liquid supplements, and silage topdressing. Iodine from other dietary sources was considered negligible. Each dairyman selected three cows each in early (<90 days), middle (90 to 120 days), and late (>120 days) lactation. Blood was collected from each cow selected, then 150 µg thyrotropin releasing hormone were given. Iodine in milk (µg/ml) and urine (µg/mg creatinine) were 2.2 and 65 for cows in high iodine herds, mote than that (.37 and 20) in low iodine herds. At resting (ng/ml) serum thyroxine was 33 and 32 and thyrotropin was 7.4 and 7.9 Serum thyroxine and tyhrotropin concentrations were increased following releasing hormone, however, increase was not affected by quantity of dietary iodine. Thyroxine in serum at resting (ng/ml)was less for cows in early lactations (25.9) than for those in middle (36.1) or late (35.5) lactation.

FOOTNOTES

1 Published with the approval of the Michigan Agricultural Experiment Station as Journal Article No. 7890.






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Copyright © 1977 by the American Dairy Science Association ®.