Doctoral Dissertations

Date of Award

12-1981

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

Eric W. Swanson

Committee Members

P.B. Coulson, J.K. Miller, R.L. Murphee, J.W. Oliver

Abstract

Holstein calves and yearlings tolerated highest doses of iodine, as EDDI, without serious effect. This represented iodine intakes of up to 600 and 2600 mg, respectively. Weight gain and feed intake of calves and yearlings were slightly depressed at the highest dosages, but this effect was not consistent among individual animals and was not statistically significant. Highest dosages of iodine may have altered slightly the thyroid function of calves, but did not affect plasma T4 and T3 of yearling heifers. Signs attributable to the expectorant action of iodine, such as nasal and lacrimal discharge, were observed at some time in most calves and yearlings. Lactating dairy cows tolerated levels of iodine up to approximately 4.5 g daily (7.5 mg per kg body weight) for 17 weeks without effect on feed intake, milk yield, or gross efficiency of milk production (feed/milk). After 17 weeks, doses of iodine were reassigned and 20 cows were administered iodine at 1.25, 2.5, or 5.0 mg per kg body weight through the lactation and dry period and four months in the subsequent lactation. Excessive iodine did not affect milk production in either lactation, and plasma T4 and T3 were not different among treatments or when compared with concentrations of six control cows, when cows were in lactation. (Plasma T4 and T3 were significantly affected by age, season, and stage of lactation.) In the dry period, plasma T4 and T3 of cows at the highest iodine dosage were consistently lower than controls. Perinatal mortality rate of calves from cows dosed with excessive iodine was markedly increased at dosages of 2.5 mg per kg body weight or greater, and at dosages of 5.0 mg per kg or greater in cows dosed only during the dry period. Plasma T4 and T3 of calves on day of birth also tended to be lower at the higher iodine dosages. In addition to effects on the developing fetus, prolonged administration of 5.0 mg iodine per kg body weight to cows through the lactation, dry period, and subsequent early lactation resulted in impaired breeding performance and an abnormally high culling rate during the second lactation.

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