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Thyroidal Uptake of I¹³¹ by Dairy Calves¹

Departments of Dairy and Physiology, Michigan State University, East Lansing

ABSTRACT

This study shows some of the factors causing variation in the 48-hr. uptake of radioactive iodine in 83 dairy calves for 2 yr. The average uptake was 36.4% of the injected dose, with considerable variation within and between trials. The Brown Swiss calves averaged 10% lower than calves of the other breeds. The highest average per cent of uptake was found in the summer, and the lowest in the spring. Hourly counts calculated as the per cent of the 24-hr. count showed little difference in the rate of uptake between breeds. A statistical analysis of the uptake of 64 Brown Swiss, Holstein, and Jersey calves showed a significant difference due to breed, season, breed x season, and other interactions. The age differences were not significant. A correlation coefficient of –0.17 was found when 37 observations of the 48-hr. uptake and the estimated thyroxine secretion rate were analyzed. The addition of iodized salt to the ration, and injecting the isotope intravenously rather than subcutaneously, had no apparent effect on the percentage of uptake. From the findings in this study and those of other workers, it appears questionable whether the thyroidal uptake of I¹³¹ alone will provide worthwhile information on the thyroid status of dairy calves.

¹ Approved by the Director, Michigan Agricultural Experiment Station, as Journal Article No. 2125.