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The Effect of Thyroidectomy and Iodine Supplementation on the Plasma PBI of a Jersey Bull

Michigan State University, East Lansing

ABSTRACT

The adoption of the plasma level of protein-bound iodine as an index of thyroid activity in dairy cattle has been hampered by uncertainty as to the proportion of the PBI which is thyroxine and the closeness with which changes in PBI reflect variations in the thyroid secretion rate.

A recent investigation of the effect of thyroidectomy on the PBI of a Jersey bull has shed some light upon these questions. The bull was thyroidectomized at 8 months of age by the subcutaneous administration of 30 mc. of carrier-free I¹³¹. Within 18 days the PBI had dropped tration was 0.8 %. During the next several months the PBI level ranged between 1.4 and 0.0 % with an average of 0.5 %.

These results suggest that the PBI of dairy cattle is closely related to thyroxine although Reece and Man (2) found that the butanol extractable iodine accounted for only 57.2% of to 3.4 % from the pretreatment level of 6.7 % (Figure 1) and on the 33rd day the concenbovine sera PBI.