Recent information on iodine deficiency in New Zealand sheep flocks

Aims. To determine the value of pasture iodine, serum thyroxine (T4) and tr i-iodothyronine (T3) concentrations and thyroid (g) to body weight (kg) rat ios in lambs as criteria to predict and diagnose increased litter size and decreased perinatal mortality in response to iodine supplementation. Methods. Results from ten iodine response trials in ewes using an oil-based intramuscular iodine preparation were reviewed along with results from inv estigations into goitre on five farms in the Manawatu. Results. In two trials, litter size was increased by 14% and 21% in iodine- treated ewes. In only three of the 10 trials was there a significant reduct ion in perinatal mortality in iodine-treated ewes. Conclusions. Pasture iodine and serum thyroxine (T4) and tri-iodothyronine (T3) concentrations appeared to be unhelpful in predicting the occurrence o f increased litter size and reduced perinatal mortality in response to iodi ne supplementation. New-born lambs from ewes not supplemented with iodine, that had a mean thyroid weight (g) to body weight (kg) ratio of 0.40 g/kg o r greater, generally had a significant increase in perinatal mortality comp ared to lambs from iodine-supplemented ewes.