The effects of fertiliser iodine application on herbage iodine concentration and animal blood levels

Two experiments were conducted to evaluate surface applications of potassiu m iodide and potassium iodate as alternatives to direct treatment of ewes w here iodine (I) deficiency may be a problem. In Experiment 1, the hypothesi s that grazing of pasture which had been sprayed with a potassium iodide an d oil mixture results in increased blood iodine (serum T-4) levels in ewes was tested over two years on five farms in Southland and West Otago, New Ze aland. The results show that spraying elevated pasture I levels from March to pre lambing. The increased pasture I levels increased serum T-4 levels b y only 1.5% in late winter, an increase which was not significant (P > 0.05 ). There were small increases in lambing percentages (1-5%) due to the spra ying in both years, but these were not significant (P > 0.05). In Experiment 2, the hypothesis that surface applications of potassium iodi de and potassium iodate fertiliser can result in increased herbage I levels was tested on two farms in Southland and West Otago in 1996 and one farm i n Central Otago in 1997. The trials ran from mid autumn (March/April) to la te winter (August/September) each year. There was a significant (P < 0.01) increase in pasture I levels after 6 weeks with both forms of iodine fertil iser, and this increase was still significant for the top application rates at the 19-week measurement (P < 0.05 for Southland and West Otago, P < 0.0 1 for Central Otago). The iodide fertiliser was slightly more effective at increasing herbage I levels than was the iodate. However, despite the effic iency of I uptake being low (4.25% of the applied I taken up by the herbage ), herbage I concentrations were lifted to acceptable levels and maintained at such for the duration of the study.